Notable locations and climbing routes on the southeast face of El Capitan. The names of each climbing route are listed at the top of the route. General locations are shaded orange. The Nose travels along the curving arête separating the sunlit and shaded parts of the cliff. The North America Wall is the concave section of wall to the right of the Nose, marked by mafic dikes in the shape of North America. The exposure visible in this image is the area of Figure 6. Location names and route paths taken from Putnam and Sloan (2014). The scale bar is an approximate horizontal scale; absolute scale varies because the image is a flattened representation of a three-dimensional surface. The view angle is to the north. Photograph courtesy of www. xRez. com. Credit: Photograph courtesy of www. xRez. com, published in Geosphere.
Granitic rocks make up much of Earth’s continental crust and many of the planet’s most iconic landscapes. However, granite’s formation is poorly understood because it happens tens of kilometers below the surface. In this unique study, authors Roger Putnam and colleagues combine decimeter-scale field mapping, rock climbing, and new dating and geochemical analyses to evaluate the timing and intrusive dynamics of the granitic rocks that make up El Capitan in Yosemite National Park, California, USA.
The comparatively accessible southeast face of El Capitan provides a clean, ~1-km-tall exposure of the interior of a granitic system. Putnam and colleagues found this vertical landscape to be a perfect place to test hypotheses regarding the formation of granitic rocks. In their paper published in Geosphere on 1 July 2015, the authors use climbing route designations as landmarks in describing the geology, along with both official and unofficial (e.g., North America; The Alcove) local place names.
They write that many models of granite formation rely on processes such as crystal/liquid segregation that should present a signature visible in the vertical dimension of a granitic system. They found that El Capitan is made up of seven different granitic units that episodically intruded over about three million years. Their chemical and textural analyses of samples collected along vertical transects of the two dominant rocks there, the El Capitan and Taft Granites, reveal no systematic patterns in rock composition. In fact, they conclude, “These data reveal [3 million years of] assembly of the plutonic system and show no evidence for gravity-driven separation of crystals and liquid over the 1 km vertical extent of the cliff,” which, they write, is “hard to reconcile with models of granite formation that envision magma chambers as large, mostly liquid, fractionating bodies.”
Reference:
Plutonism in three dimensions: Field and geochemical relations on the southeast face of El Capitan, Yosemite National Park, California
Roger Putnam et al., University of North Carolina, Chapel Hill, North Carolina, USA. Published online on 1 July 2015; DOI: 10.1130/GES01133.1.
Graduate student Elena Steponaitis takes notes while collecting stalagmite and drip water samples in Lehman Caves, Nevada. Credit: Christine Y. Chen
All around the deserts of Utah, Nevada, southern Oregon, and eastern California, ancient shorelines line the hillsides above dry valley floors, like bathtub rings—remnants of the lakes once found throughout the region. Even as the ice sheets retreated at the end of the last ice age, 12,000 years ago, the region remained much wetter than it is today. The earliest settlers of the region are likely to have encountered a verdant landscape of springs and wetlands.
So just when and why did today’s desert West dry out?
Researchers from MIT and elsewhere have now determined that the western U.S.—a region including Nevada, Utah, Oregon, and parts of California—was a rather damp setting until approximately 8,200 years ago, when the region began to dry out, eventually assuming the arid environments we see today.
The team identified this climatic turning point after analyzing stalagmites from a cave in Great Basin National Park in Nevada. Stalagmites are pillars of deposited cave drippings that form over hundreds of thousands of years, as water slowly seeps down through the ground, and into caves. A stalagmite’s layers are essentially a record of a region’s moisture over time.
The researchers used a dating technique to determine the ages of certain layers within two stalagmites, then analyzed these layers for chemical signatures of moisture. They dated stalagmite layers ranging from 4,000 to 16,000 years old, observing that moisture content appears to drop dramatically in samples that are less than 8,200 years old.
David McGee, the Kerr-McGee Career Development Assistant Professor in MIT’s Department of Earth, Atmospheric and Planetary Sciences, says the results suggest that around 8,200 years ago, the climate of the American West began transitioning from a lush landscape to the desert terrain that we know today. On a geological timescale, McGee says the region’s moisture content appears to have dropped rather suddenly—”like falling off a shelf,” he says. This steep drop likely had a dramatic impact on humans living in the region.
“Based upon these data, I would hypothesize that you should see some pretty big changes in how people were living just before and right after 8,000 years ago,” McGee says. “What sort of game were they hunting, what plants were they eating, and where were they choosing to live? Montana’s going to start looking pretty good if the Great Basin is drying out. ”
McGee and graduate students Elena Steponaitis and Alexandra Andrews have published their findings in the journal Quaternary Science Reviews.
McGee and his colleagues concentrated their study on a single cave on the eastern edge of Nevada, known as Lehman Caves, that is part of the Great Basin National Park. A rancher discovered the cave in 1885, and carved a path through its stalagmites, ultimately turning the cave into a tourist attraction. Park rangers have since collected the broken stalagmites, reassembling and storing them in a “library” within the cave.
In 2012, Steponaitis led a group through the cave to look for stalagmites—also known as “speleothems”—that may pinpoint when the western U.S. began to dry out. The researchers formed an assembly line of sorts, methodically labeling and photographing the top and bottom shards of each stalagmite stored in the cave’s library. The group then took these shards into the lab to determine their ages.
To date the shards, the researchers drilled into each stalagmite shard, creating a powder that they then analyzed for isotopes of uranium and thorium. As uranium decays to thorium at a known rate, the ratio of the two isotopes can indicate a layer’s age, or when it first was deposited.
“[Stalagmites] are deposited in layers, kind of like stacked traffic cones,” McGee says. “Each year’s drips make a new coating, and when you cut them open, they have a very clear set of layers, and a clear sense of this is older, this is younger. So they have stratigraphy to them, which is important to us.”
After dating each shard, McGee and Steponaitis singled out two stalagmite samples that were deposited within the last 15,000 years, suggesting these stalagmites were formed toward the end of the last Ice Age. Within each stalagmite, the group dated and marked layers at regular intervals.
Percolating through a cave
To determine the moisture content for each layer, the researchers first examined how water traveled through the cave. They collected drips from various locations throughout the cave, water from standing pools on the cave floor, and soil samples from above the cave.
“I’ve heard stalagmites called ‘fossilized groundwater,’ and that’s essentially what they are,” McGee says. “Groundwater is percolating through the soil and rock, gets to the cave and drips out, and precipitates this stalagmite. The chemistry of that groundwater tells us something about the conditions outside the cave.”
For this particular cave, the researchers observed that the drier the soil above a cave, the slower the percolation of water down into the cave. Water in soil tends to precipitate calcium, leaving more magnesium in the water that reaches the cave. The group analyzed each stalagmite for magnesium, reasoning that the more magnesium found in a particular layer, the drier that period of time was, and vice versa.
Their experiments showed that magnesium levels rose rapidly in layers deposited after roughly 8,200 years ago, indicating that this period experienced a significant drying event. What that event might be is up for debate, although McGee hazards a guess.
“One of the big things that was happening at this time worldwide was the collapse of the last vestiges of this big ice sheet in Canada,” McGee says. “An ice sheet is thought to have important effects on where the jet stream goes. By having this ice sheet here, it made it so the jet stream was more likely to bring storms into the American West, and when it collapsed, the region became more like it is today.”
The team found that lake records from Nevada, Utah, Oregon, and eastern California suggest a similar drying-out period. “Further work will help us figure out exactly what that fingerprint is,” McGee says.
Reference:
“Mid-Holocene drying of the U.S. Great Basin recorded in Nevada speleothems,” Quaternary Science Reviews, Available online 11 June 2015, ISSN 0277-3791, DOI: 10.1016/j.quascirev.2015.04.011
The snake has small ‘hands’ that are approx 1cm long. Credit: Image courtesy of University of Portsmouth
An “absolutely exquisite” fossil of a snake that had four legs has been discovered by a team of scientists and may help show how snakes made the transition from lizards to serpents.
It is the first known fossil of a four-legged snake, and the team — led by Dr Dave Martill from the University of Portsmouth — say that this discovery could help scientists to understand how snakes lost their legs.
The findings were published in the journal Science.
Dr Martill said: “It is generally accepted that snakes evolved from lizards at some point in the distant past. What scientists don’t know yet is when they evolved, why they evolved, and what type of lizard they evolved from. This fossil answers some very important questions, for example it now seems clear to us that snakes evolved from burrowing lizards, not from marine lizards.”
The fossil, from Brazil, dates from the Cretaceous period and is 110 million years old, making it the oldest definitive snake.
Dr Martill discovered the fossil as part of a routine field trip with students to Museum Solnhofen, Germany, a museum that is well-known for its prestige with regard to fossils.
Dr Martill said: “The fossil was part of a larger exhibition of fossils from the Cretaceous period. It was clear that no-one had appreciated its importance, but when I saw it I knew it was an incredibly significant specimen.”
Dr Martill worked with expert German palaeontologist Helmut Tischlinger, who prepared and photographed the specimen, and Dr Nick Longrich from the University of Bath’s Milner Centre for Evolution, who studied the evolutionary relationships of the snake.
Dr Longrich, who had previously worked on snake origins, became intrigued when Martill told him the story over a pint at the local pub in Bath.
He said: “A four-legged snake seemed fantastic and as an evolutionary biologist, just too good to be true, it was especially interesting that it was put on display in a museum where anyone could see it.”
He said he was initially sceptical, but when Dr Martill showed him Tischlinger’s photographs, he knew immediately that it was a fossil snake.
The snake, named Tetrapodophis amplectus by the team, is a juvenile and very small, measuring just 20cm from head to toe, although it may have grown much larger. The head is the size of an adult fingernail, and the smallest tail bone is only a quarter of a millimetre long. But the most remarkable thing about it is the presence of two sets of legs, or a pair of hands and a pair of feet.
The front legs are very small, about 1cm long, but have little elbows and wrists and hands that are just 5mm in length. The back legs are slightly longer and the feet are larger than the hands and could have been used to grasp its prey.
Dr Longrich said: “It is a perfect little snake, except it has these little arms and legs, and they have these strange long fingers and toes.
“The hands and feet are very specialised for grasping. So when snakes stopped walking and started slithering, the legs didn’t just become useless little vestiges — they started using them for something else. We’re not entirely sure what that would be, but they may have been used for grasping prey, or perhaps mates.”
Interestingly, the fossilised snake also has the remains of its last meal in its guts, including some fragments of bone. The prey was probably a salamander, showing that snakes were carnivorous much earlier in evolutionary history than previously believed.
Helmut Tischlinger said: “The preservation of the little snake is absolutely exquisite. The skeleton is fully articulated. Details of the bones are clearly visible and impressions of soft tissues such as scales and the trachea are preserved.”
Tetraphodophis has been categorised as a snake, rather than a lizard, by the team due to a number of features:
The skeleton has a lengthened body, not a long tail.
The tooth implantation, the direction of the teeth, and the pattern of the teeth and the bones of the lower jaw are all snake-like.
The fossil displays hints of a single row of belly scales, a sure fire way to differentiate a snake from a lizard.
Tetrapodophis would have lived on the bank of a salt lake, in an arid scrub environment, surrounded by succulent plants. It would probably have lived on a diet of small amphibians and lizards, trying to avoid the dinosaurs and pterosaurs that lived there.
At the time, South America was united with Africa as part of a supercontinent known as Gondwana. The presence of the oldest definitive snake fossil in Gondwana suggests that snakes may originally have evolved on the ancient supercontinent, and only became widespread much more recently.
Video
An “absolutely exquisite” fossil of a snake that had four legs has been discovered by a team of scientists and may help show how snakes made the transition from lizards to serpents.
Dr Dave Martill from the University of Portsmouth worked with expert German palaeontologist Helmut Tischlinger, and Dr Nick Longrich from the University of Bath’s Milner Centre for Evolution. Dr Dave Martill explains
Reference:
Dave Martill et al. A four-legged snake from the Early Cretaceous of Gondwana. Science, July 2015 DOI: 10.1126/science.aac5672
Mammoth vertebrae in ice, Yukon Territory, Canada. Credit: Kieren Mitchell, University of Adelaide
New research has revealed abrupt warming, that closely resembles the rapid human-made warming occurring today, has repeatedly played a key role in mass extinction events of large animals, the megafauna, in Earth’s past.
Using advances in analysing ancient DNA, radiocarbon dating and other geologic records an international team led by researchers from the University of Adelaide and the University of New South Wales (Australia) have revealed that short, rapid warming events, known as interstadials, recorded during the last ice age or Pleistocene (60,000-12,000 years ago) coincided with major extinction events even before the appearance of man.
Published today in Science, the researchers say by contrast, extreme cold periods, such as the last glacial maximum, do not appear to correspond with these extinctions.
“This abrupt warming had a profound impact on climate that caused marked shifts in global rainfall and vegetation patterns,” said University of Adelaide lead author and Director of the Australian Centre for Ancient DNA, Professor Alan Cooper.
“Even without the presence of humans we saw mass extinctions. When you add the modern addition of human pressures and fragmenting of the environment to the rapid changes brought by global warming, it raises serious concerns about the future of our environment.”
The researchers came to their conclusions after detecting a pattern, 10 years ago, in ancient DNA studies suggesting the rapid disappearance of large species. At first the researchers thought these were related to intense cold snaps.
However, as more fossil-DNA became available from museum specimen collections and through improvements in carbon dating and temperature records that showed better resolution through time, they were surprised to find the opposite. It became increasingly clear that rapid warming, not sudden cold snaps, was the cause of the extinctions during the last glacial maximum.
The research helps explain further the sudden disappearance of mammoths and giant sloths that became extinct around 11,000 years ago at the end of the last ice age.
“It is important to recognize that man still played an important role in the disappearance of the major mega fauna species,” said fellow author Professor Chris Turney from the University of New South Wales.
“The abrupt warming of the climate caused massive changes to the environment that set the extinction events in motion, but the rise of humans applied the coup de grace to a population that was already under stress.”
In addition to the finding, the new statistical methods used to interrogate the datasets (led by Adelaide co-author Professor Corey Bradshaw) and the new data itself has created an extraordinarily precise record of climate change and species movement over the Pleistocene.
This new dataset will allow future researchers a better understanding of this important period than has ever been possible before.
Reference:
Alan Cooper, Chris Turney, Konrad A. Hughen, Barry W. Brook, H. Gregory McDonald, and Corey J. A. Bradshaw. Abrupt warming events drove Late Pleistocene Holarctic megafaunal turnover. Science, 23 July 2015 DOI: 10.1126/science.aac4315
Images showing the back-projected power and path of the Nepal earthquake. Credit: Wenyuan Fan and Peter Shearer
Researchers from Scripps Institution of Oceanography at UC San Diego have accurately mapped out the movement of the devastating 7.8-magnitude Nepal earthquake that killed over 9,000 and injured over 23,000 people. Scientists have determined that the earthquake was a rupture consisting of three different stages. The study could help a rapidly growing region understand its future seismic risks.
The Himalayan region is particularly prone to earthquakes and this study will serve as an important benchmark for understanding where future earthquakes may occur, especially since the area has experienced high population growth over the past few decades.
The study assessed the presence of low frequency and high frequency waves over the three stages of the earthquake. High frequency waves cause more shaking, thereby posing the greatest risks for structural damages. Low frequency waves are less violent and less damaging to buildings and infrastructure.
“The Nepal earthquake is a warning sign that the region is of high seismic risk, and each earthquake behaves differently. Some earthquakes jump from one fault line to another, whereas the Nepal quake apparently occurred on the same fault line in three different stages, moving eastward,” said Scripps geophysicist Peter Shearer, “Using this research, we can better understand and identify areas of high seismic hazard in the region.”
This first peer-reviewed study on the April 2015 earthquake in Nepal, “Detailed rupture imaging of the 25 April 2015 Nepal earthquake using teleseismic P waves” was published online July 16 in the American Geophysical Union (AGU) journal Geophysical Research Letters.
Using the Global Seismic Network (GSN), Shearer and Scripps graduate student Wenyuan Fan were able to unravel the complex evolution of fault slips during this earthquake. The study concludes that the rupture traveled mostly eastward and occurred in three distinct stages; Stage 1 was weak and slow; Stage 2 was near Kathmandu and had the greatest slip but was relatively deficient in high-frequency radiation; and Stage 3 was relatively slow as well. Overall, this earthquake was more complicated, with multi-stage movements on multiple faults, than smooth models of continuous rupture on a single fault plane.
“Using the GSN instead of regional array data really enhanced the spatial resolution of the back-projection images and helped us see that frequency-dependent rupture was one of the main features of this earthquake,” said Fan. “Stage 2 was high-frequency-deficient and occurred closest to Kathmandu, which was probably why ground shaking was less severer than expected for such a high-magnitude earthquake.”
The Global Seismic Network provides high-quality broadband digital seismic data for monitoring earthquakes and learning about Earth structure. A precursor to this network was initiated by Scripps researchers in the 1960s and is still in use today. Scripps currently operates one-third of the 153 global seismometers of the GSN. Fan and Shearer used the GSN data because they are open-source (available to anyone), have good coverage of the Nepal region, and have a long history of reliable recordings.
“In general, understanding large earthquakes will inform our ability to forecast the nature of future earthquakes,” said Shearer.
Shearer and Fan hope to use the same methodology to study other large, global earthquakes from the past decade to provide a broader picture of earthquake behavior and help in predicting ground shaking for future events.
Reference:
Wenyuan Fan, Peter M. Shearer. Detailed rupture imaging of the 25 April 2015 Nepal earthquake using teleseismicPwaves. Geophysical Research Letters, 2015; DOI: 10.1002/2015GL064587
A gigantic sunspot almost 130,000 km across captured by NASA’s Solar Dynamic Observatory on October 23, 2014. Credit: NASA/SD
This month there’s been a hoopla about a mini ice age, and unfortunately it tells us more about failures of science communication than the climate. Such failures can maintain the illusion of doubt and uncertainty, even when there’s a scientific consensus that the world is warming.
The story starts benignly with a peer-reviewed paper and a presentation in early July by Professor Valentina Zharkova, from Northumbria University, at Britain’s National Astronomy Meeting.
The paper presents a model for the sun’s magnetic field and sunspots, which predicts a 60% fall in sunspot numbers when extrapolated to the 2030s. Crucially, the paper makes no mention of climate.
The first failure of science communication is present in the Royal Astronomical Society press release from July 9. It says that “solar activity will fall by 60 per cent during the 2030s” without clarifying that this “solar activity” refers to a fall in the number of sunspots, not a dramatic fall in the life-sustaining light emitted by the sun.
The press release also omits crucial details. It does say that the drop in sunspots may resemble the Maunder minimum, a 17th century lull in solar activity, and includes a link to the Wikipedia article on the subject. The press release also notes that the Maunder minimum coincided with a mini ice age.
But that mini ice age began before the Maunder minimum and may have had multiple causes, including volcanism.
Crucially, the press release doesn’t say what the implications of a future Maunder minimum are for climate.
How would a new Maunder minimum impact climate? It’s an obvious question, and one that climate scientists have already answered. But many journalists didn’t ask the experts, instead drawing their own conclusions.
The UK’s Telegraph warned:
[…] the earth is 15 years from a mini ice age that will cause bitterly cold winters during which rivers such as the Thames freeze over.
Pictures of glaciers and frozen rivers loomed large.
News Corp’s Andrew Bolt used the mini ice age to attack climate science. Many climate sceptic bloggers readily accepted the story, despite climate never being mentioned in the peer-reviewed paper.
The media failed in its duty to investigate and inform. It didn’t seek expert comment to put the research into context. Instead journalists tried to answer technical climate science questions themselves, and mostly got it wrong.
As discussed previously, the impact of a new Maunder minimum on climate has beenstudied many times. There’s 40% more CO2 in the air now than during the 17th century, and global temperature records are being smashed. A new Maunder minimum would slow climate change, but it is not enough to stop it.
The scientist at the centre of the media storm, Valentina Zharkova, told USA today:
In the press release, we didn’t say anything about climate change. My guess is when they heard about Maunder minimum, they used Wikipedia or something to find out more about it.
Mixed messages
While Zharkova was surprised by the media coverage, she and others continued to discuss a new mini ice age.
If a mini ice age is at odds with the prior literature, why does Zharkova continue speculating about it? In personal correspondence with Zharkova, she told me it was only after the media coverage that her research was connected to climate change and the Maunder minimum. However, she said that once the connection was made, it did make sense to her.
Zharkova also told IFLS: We didn’t mention anything about the weather change, but I would have to agree that possibly you can expect it [a mini ice age].
So it seems Zharkova’s justification is based on media extrapolation of her own press release and Wikipedia, not the extensive peer-reviewed literature on the Maunder minimum itself.
I emailed Zharkova and she sent me two studies that support her views, but they aren’t representative of the literature and I don’t believe she has critically evaluated their content.
Is there any quantitative basis for claims of a mini ice age? Zharkova and her colleagues have cited a 1997 article by Judith Lean, who showed the sun’s brightness (quantified by solar irradiance) was 3 W per m2 less during the Maunder minimum than today. More recent studies, including those by Lean, find the solar irradiance varies less than was thought in 1997.
In plain English, the small change in sunlight reaching the Earth during a new Maunder minimum wouldn’t be enough to reverse climate change. For the technically minded, even a 3 W per m2 change in irradiance corresponds to a radiative forcing of just 0.5 W per m2 (because the Earth is a sphere and not a flat circle), which is less than the radiative forcing produced by anthropogenic greenhouse gases.
To be blunt: no mini ice age for us. The real story of the impending mini ice age isn’t about climate at all. It is a cautionary tale, of how science should and shouldn’t be communicated.
The lessons to be learned from this is scientists must communicate their science concisely and accurately, especially if we are to avoid the media frenzy highlighted by the ABC’s Media Watch. If scientists, science organisations and media aren’t careful, they can inadvertently end up promoting dangerous misinformation.
Note: The above post is reprinted from materials provided by The Conversation. This story is published courtesy of The Conversation (under Creative Commons-Attribution/No derivatives).The Conversation
Research by University of Reading scientists into climatic patterns from the past 1,000 years has improved our understanding of how the weather in Europe could respond to changes in the future.
In a letter published in Nature, Dr Pablo Ortega from the National Centre for Atmospheric Science (NCAS), based in the University of Reading’s Department of Meteorology, and other European colleagues present an unprecedented annually resolved reconstruction of the NAO evolution during the past millennium.
The North Atlantic Oscillation (NAO) describes a seesaw in atmospheric pressure between the regions of the Azores High and the Icelandic Low that controls the flow of winter storms across the Atlantic. It has therefore large impacts on winter climate temperature over Europe.
When the difference in pressure between Azores and Iceland is stronger than normal the NAO enters a positive phase and Atlantic storms are directed towards the British Isles and Northern Europe, carrying precipitation and warmer temperatures, and keep the Mediterranean region on the dry side.
Climate prediction
Recent developments in climate models offer promise to predict the NAO evolution and therefore the climate over Europe from one season to another. However, the lack of long direct observations prevents the assessment of its predictability at longer lead times (years to decades).
This latest reconstruction, carried out at Dr Ortega’s previous institution the LSCE/CEA (France), relies on the combination and analysis of climate information from 48 different natural archives or “proxies” distributed around the Atlantic Ocean, including tree rings, speleothems, ice cores and lake sediments.
The final reconstruction indicates that the NAO phase was predominantly positive during the 13th and 14th centuries, but not during the whole medieval period as a previous analysis suggested to explain the unusually warm temperatures in Northern Europe at the time. This former analysis, based only on two natural archives, is also debated by other documentary sources in Europe. To further support their findings, Dr Ortega and colleagues have mimicked and compared both reconstruction approaches in climate simulations with six different state-of-the-art climate models. Their analysis is conclusive; all the models support the new reconstruction as a more reliable estimation of past NAO variability.
“This validation with models is a novel encouraging approach for the paleoclimatology community”, Dr Ortega explains.
“Up to now, natural archives have been used to assess the ability of climate models to reproduce past climate variability. Our study has shown the added value of using models to test the reliability of paleoclimate reconstructions.”
Another important result, with implications for climate prediction over Europe, is the identification of a systematic NAO response to volcanic eruptions. In the reconstruction, positive NAO phases emerge two years after strong volcanic eruptions, consistent with satellite observations for the Mt Pinatubo eruption in the Philippines.
Reference:
“A model-tested North Atlantic Oscillation reconstruction for the past millennium.” Nature 523, 71–74 (02 July 2015) DOI: 10.1038/nature14518
A variety of deltas: the Mississippi birdfoot delta (right) and Mexico’s Grijalva cuspate delta (left). Credit: NASA Landsat
The Mississippi River delta is a rich ecosystem of barrier islands, estuaries, and wetlands that’s home to a diverse mix of wildlife—as well as more than 2 million people. Over the past few decades, the shape of the delta has changed significantly, as ocean waves have carved away at the coastline, submerging and shrinking habitats.
To keep flooding at bay, engineers have erected dams and levees along the river. However, it’s unclear how such protective measures will affect the shape of the river delta, and its communities, over time.
Now researchers from MIT and the Woods Hole Oceanographic Institution (WHOI) have devised a simple way to predict a river delta’s shape, given two competing factors: its river’s force in depositing sediment into the ocean, and ocean waves’ strength in pushing that sediment back along the coast. Depending on the balance of the two, the coastline of a river delta may take on a smooth “cuspate” shape, or a more pointed “crenulated” outline, resembling a bird’s foot.
The new metric may help engineers determine how the shape of a delta, such as the Mississippi’s, may shift in response to engineered structures such as dams and levees, and environmental changes, such as hurricane activity and sea-level rise.
Jaap Nienhuis, a graduate student in the MIT-WHOI Joint Program in Marine Geology and Geophysics, says the effects of climate change, and the human efforts to combat these effects, are already making an impact on river deltas around the world.
“Because there are so many people living on a river delta, you want to know what its morphology or shape will look like in the future,” Nienhuis says. “For the Mississippi, the river supplies a lot of sediment. But because there are a lot of dams on the Mississippi nowadays, there is not as much sand coming down the river, so people are very worried about how this delta will evolve, especially with sea-level rise, over the coming centuries.”
Nienhuis, and Andrew Ashton and Liviu Glosan of WHOI, report their results in the journal Geology.
Over hundreds of thousands of years, a river’s sand and silt flow toward the coast, ultimately piling up at a river’s mouth in the form of a low-lying delta. A delta’s coastline can be relatively smooth, with most sand depositing from the main river, or it can fan out in the shape of a bird’s foot, as the river bifurcates into tributaries and channels, each of which deposits sand in finger-like projections.
Scientists often characterize a delta as either river-dominated or wave-dominated.
In a wave-dominated delta, such as the Nile River delta in Egypt, incoming ocean waves are stronger than the river’s flow. As a result, waves push outflowing sediment back along the coast, effectively smoothing the coastline. By contrast, a river-dominated delta, such as the Mississippi’s, is shaped by a stronger river, which deposits sand faster than ocean waves can push back, creating a crenulated coastline.
While this relationship between rivers and ocean waves is generally understood, Nienhuis says there is no formal way to determine when a delta will tip toward a smooth or pointy shape.
The researchers came up with a simple ratio to predict a delta’s shape, based on a river’s sediment flux, or the flow rate of sediment through a river, and the strength of ocean waves, determined by a wave’s height, frequency, and angle of approach.
Based on the various factors that determine the overall ratio, the team determined the point at which a delta would no longer be a smooth outline, shaped by ocean waves, but instead, a pointy coastline, influenced more by the river.
“At some point there’s so much sediment that you exceed the maximum of what waves can do,” Nienhuis says, “and then you become a ‘bird foot,’ or river-dominated delta, because the river is so much stronger.”
A delta’s tipping point
Nienhuis and his colleagues applied the new method to 25 river deltas on the north shore of the Indonesian island of Java, a region where sediments have deposited on a shallow continental shelf, creating a wide variety of delta shapes.
For each delta, the team used a global wave model developed by the National Oceanic and Atmospheric Administration to determine the height, frequency, and direction of each incoming wave. The researchers also used a model to determine the corresponding river’s sediment flux.
Using data from both models, Nienhuis determined the ratio of river-to-ocean wave strength for each delta, and found that those deltas with a ratio greater than or equal to 1 were more likely to have multiple river channels, with deltas that project out from the shoreline. The main factor determining this transition turned out to be the angle at which ocean waves generally approach the coast: If the angle of approach is 45 degrees or greater, then ocean waves are no longer able to smooth out the amount of sediment coming from a river, tipping a delta’s shape toward a river-dominated morphology.
Nienhuis says the group’s method may help engineers predict the shape a delta may take if erected dams or levees change a river’s sediment flow. Similarly, the method may estimate the evolution of deltas with climate change, as rising sea levels and increased hurricane activity will likely alter the behavior and magnitude of ocean waves.
Douglas Edmonds, an assistant professor of geological sciences at Indiana University who was not involved in the research, says the new model “is a powerful advance, because it allows engineers and environmental managers to make informed predictions about how to restore deltas that are drowning. For example, in places like coastal Louisiana, substantial funds are needed to divert water and sediment from rivers into drowning areas to build new deltaic land. To make sure these diversions are successful, we need to predict how that new deltaic land will evolve. Nienhuis et al. have provided an important blueprint toward that end.”
Reference:
“What makes a delta wave-dominated?” Geology, June 2015, v. 43, p. 511-514, first published on April 27, 2015, DOI: 10.1130/G36518.1
Compared to its celestial neighbours Venus and Mars, Earth is a pretty habitable place. So how did we get so lucky? A new study sheds light on the improbable evolutionary path that enabled Earth to sustain life.
The research, published this week in Nature Geoscience, suggests that Earth’s first crust, which was rich in radioactive heat-producing elements such as uranium and potassium, was torn from the planet and lost to space when asteroids bombarded the planet early in its history. This phenomenon, known as impact erosion, helps explain a landmark discovery made over a decade ago about the Earth’s composition.
Researchers with the University of British Columbia and University of California, Santa Barbara say that the early loss of these two elements ultimately determined the evolution of Earth’s plate tectonics, magnetic field and climate.
“The events that define the early formation and bulk composition of Earth govern, in part, the subsequent tectonic, magnetic and climatic histories of our planet, all of which have to work together to create the Earth in which we live,” said Mark Jellinek, a professor in the Department of Earth, Ocean & Atmospheric Sciences at UBC. “It’s these events that potentially differentiate Earth from other planets.”
On Earth, shifting tectonic plates cause regular overturning of Earth’s surface, which steadily cools the underlying mantle, maintains the planet’s strong magnetic field and stimulates volcanic activity. Erupting volcanoes release greenhouse gases from deep inside the planet and regular eruptions help to maintain the habitable climate that distinguishes Earth from all other rocky planets.
Venus is the most similar planet to Earth in terms of size, mass, density, gravity and composition. While Earth has had a stable and habitable climate over geological time, Venus is in a climate catastrophe with a thick carbon dioxide atmosphere and surface temperatures reaching about 470 C. In this study, Jellinek and Matt Jackson, an associate professor at the University of California, explain why the two planets could have evolved so differently.
“Earth could have easily ended up like present day Venus,” said Jellinek. “A key difference that can tip the balance, however, may be differing extents of impact erosion.”
With less impact erosion, Venus would cool episodically with catastrophic swings in the intensity of volcanic activity driving dramatic and billion-year-long swings in climate.
“We played out this impact erosion story forward in time and we were able to show that the effect of the conditions governing the initial composition of a planet can have profound consequences for its evolution. It’s a very special set of circumstances that make Earth.”
Reference:
A. M. Jellinek, M. G. Jackson. Connections between the bulk composition, geodynamics and habitability of Earth. Nature Geoscience, 2015; DOI: 10.1038/ngeo2488
Topography (left) and a shaded relief map (right) of the rock deep beneath the Tibetan Plateau. Color indicates kilometers below Earth’s surface. Credit: Image by Younghong Shin of the Korea Institute of Geosciences and Mineral Resource, courtesy of The Ohio State University.
Gravity data captured by satellite has allowed researchers to take a closer look at the geology deep beneath the Tibetan Plateau.
The analysis, published in the journal Nature Scientific Reports, offers some of the clearest views ever obtained of rock moving up to 50 miles below the plateau, in the lowest layer of Earth’s crust.
There, the Indian tectonic plate presses continually northward into the Eurasian tectonic plate, giving rise to the highest mountains on Earth — and deadly earthquakes, such as the one that killed more than 9,000 people in Nepal earlier this year.
The study supports what researchers have long suspected: Horizontal compression between the two continental plates is the dominant driver of geophysical processes in the region, said C.K. Shum, professor and Distinguished University Scholar in the Division of Geodetic Science, School of Earth Sciences at The Ohio State University and a co-author of the study.
“The new gravity data onboard the joint NASA-German Aerospace Center GRACE gravimeter mission and the European Space Agency’s GOCE gravity gradiometer mission enabled scientists to build global gravity field models with unprecedented accuracy and resolution, which improved our understanding of the crustal structure,” Shum said. “Specifically, we’re now able to better quantify the thickening and buckling of the crust beneath the Tibetan Plateau.”
Shum is part of an international research team led by Younghong Shin of the Korea Institute of Geosciences and Mineral Resource. With other researchers in Korea, Italy and China, they are working together to conduct geophysical interpretations of the Tibetan Plateau geodynamics using the latest combined gravity measurements by the GOCE gravity gradiometer and the GRACE gravimeter missions.
Satellites such as GRACE and GOCE measure small changes in the force of gravity around the planet. Gravity varies slightly from place to place in part because of an uneven distribution of rock in Earth’s interior.
The resulting computer model offers a 3-D reconstruction of what’s happening deep within earth.
As the two continental plates press together horizontally, the crust piles up. Like traffic backing up on a congested freeway system, the rock follows whatever side roads may be available to relieve the pressure.
But unlike cars on a freeway, the rock beneath Tibet has two additional options for escape. It can push upward to form the Himalayan mountain chain, or downward to form the base of the Tibetan Plateau.
The process takes millions of years, but caught in the 3-D image of the computer model, the up-and-down and side-to-side motions create a complex interplay of wavy patterns at the boundary between the crust and the mantle, known to researchers as the Mohorovičić discontinuity, or “Moho.”
“What’s particularly useful about the new gravity model is that it reveals the Moho topography is not random, but rather has a semi-regular pattern of ranges and folds, and agrees with the ongoing tectonic collision and current crustal movement measured by GPS,” Shin said.
As such, the researchers hope that the model will provide new insights into the analysis of collisional boundaries around the world.
Co-author Carla Braitenberg of the University of Trieste said that the study has already helped explain one curious aspect of the region’s geology: the sideways motion of the Tibetan Plateau. While India is pushing the plateau northward, GPS measurements show that portions of the crust are flowing eastward and even turning to the southeast.
“The GOCE data show that the movement recorded at the surface has a deep counterpart at the base of the crust,” Braitenberg said. Connecting the rock flow below to movement above will help researchers better understand the forces at work in the region.
Those same forces led to the deadly Nepal earthquake in April 2015. But Shum said that the new model almost certainly won’t help with earthquake forecasting — at least not in the near future.
“I would say that we would understand the mechanism more if we had more measurements,” he said, but such capabilities “would be very far away.”
Even in California — where, Shum pointed out, different tectonic processes are at work than in Tibet — researchers are unable to forecast earthquakes, despite having abundant GPS, seismic and gravity data. Even less is known about Tibet, in part because the rough terrain makes installing GPS equipment difficult.
Other co-authors on the study included Sang Mook Lee of Seoul National University; Sung-Ho Na of the University of Science and Technology in Daejeon, Korea; Kwang Sun Choi of Pusan National University; Houtse Hsu of the Institute of Geodesy & Geophysics, Chinese Academy of Sciences; and Young-Sue Park and Mutaek Lim of the Korea Institute of Geosciences and Mineral Resource.
This research was supported by the Basic Research Project of the Korea Institute of Geoscience and Mineral Resources, funded by the Ministry of Science, ICT and Future Planning of Korea. Shum was partially supported by NASA’s GRACE Science Team Program and Concept in Advanced Geodesy Program. Braitenberg was partially supported by the European Space Agency’s Center for Earth Observation as part of the GOCE User ToolBox project.
Reference:
Young Hong Shin, C.K. Shum, Carla Braitenberg, Sang Mook Lee, Sung -Ho Na, Kwang Sun Choi, Houtse Hsu, Young-Sue Park, Mutaek Lim. Moho topography, ranges and folds of Tibet by analysis of global gravity models and GOCE data. Scientific Reports, 2015; 5: 11681 DOI: 10.1038/srep11681
Note: The above post is reprinted from materials provided by Ohio State University. The original item was written by Pam Frost Gorder.
The migration route of Siberians into North America and the subsequent split into northern and southern Amerindian populations. Analysis of current and ancient genomes shows that there also was some later interbreeding between East Asians and Inuit.
The original Americans came from Siberia in a single wave no more than 23,000 years ago, at the height of the last Ice Age, and apparently hung out in the north — perhaps for thousands of years — before spreading in two distinct populations throughout North and South America, according to a new genomic analysis.The findings, which will be reported in the July 24 issue of Science, confirm the most popular theory of the peopling of the Americas, but throws cold water on others, including the notion of an earlier wave of people from East Asia prior to the last glacial maximum, and the idea that multiple independent waves produced the major subgroups of Native Americans we see today, as opposed to diversification in the Americas.
This Ice Age migration over a land bridge between Siberia and Alaska is distinct from the arrival of the Inuit and Eskimo, who were latecomers, spreading throughout the Artic beginning about 5,500 years ago.
The findings also dispel the idea that Polynesians or Europeans contributed to the genetic heritage of Native Americans.
The analysis, using the most comprehensive genetic data set from Native Americans to date, was conducted using three different statistical models, two of them created by UC Berkeley researchers. The first, developed by the lab of Yun Song, a UC Berkeley associate professor of statistics and of electrical engineering and computer sciences, takes into account the full DNA information available from the genomes in the study. A second method, developed by Rasmus Nielsen, a UC Berkeley professor of integrative biology, and graduate student Kelley Harris, requires much less computation, but relies on a summary of the genome data. These and a third method developed by researchers at the Wellcome Trust Sanger Institute, England, all yielded consistent results. Song and Nielsen are two of three corresponding authors of the paper.
Modern and ancient genomes
The data consisted of the sequenced genomes of 31 living Native Americans, Siberians and people from around the Pacific Ocean, and the genomes of 23 ancient individuals from North and South America, spanning a time between 200 and 6,000 years ago.
“There is some uncertainty in the dates of the migration and the divergence between the norther and southern Amerindian populations,” Song noted, “but as we get more ancient genomes sequenced, we will be able to put more precise dates on the times of migration.”
The international team concluded that the northern and southern Native American populations diverged between 11,500 and 14,500 years ago, with the northern branch leading to the present day Athabascans and Amerindians broadly distributed throughout North America. The southern branch peopled Central and South America, as well as part of northern North America.
“The diversification of modern Native Americans appears to have started around 13,000 years ago when the first unique Native American culture appears in the archeological record: the Clovis culture,” said Nielsen. “We can date this split so precisely in part because we previously have analyzed the 12,600-year-old remains of a boy associated with the Clovis culture.”
One surprise in the genetic data is that both populations of Native Americans have a small admixture of genes from East Asians and Australo-Melanesians, including Papuans, Solomon Islanders and Southeast Asian hunter gatherers.
“It’s a surprising finding and it implies that New World populations were not completely isolated from the Old World after their initial migration,” said Eske Willerslev from the Centre for GeoGenetics at the Natural History Museum, University of Copenhagen, who headed the study. “We cannot say exactly how and when this gene flow happened, but one possibility is that it came through the Aleutian Islanders living off the coast of Alaska.”
Song added that the state-of-the-art statistical methods that his and Nielsen’s labs developed “are being made publicly available so that they can be used by others to study complex demographic histories of other populations.
Reference:
Maanasa Raghavan at al. Genomic evidence for the Pleistocene and recent population history of Native Americans. Science, 2015 DOI: 10.1126/science.aab3884
Note: The above post is reprinted from materials provided by University of California – Berkeley. The original item was written by Robert Sanders.
Hidden secrets about life in Somerset 190 million years ago have been revealed by researchers at the University of Bristol and the Bath Royal Literary and Scientific Institution (BRLSI) in a new study of some remarkable fossils. Thanks to exceptional conditions of preservation, a whole marine ecosystem has been uncovered — and yet it was already known 150 years ago.
The fossils come from Strawberry Bank in Ilminster, Somerset, but the site has now been lost, having been built over. They were discovered by noted Bath-based geologist Charles Moore (1815-1881), who first spotted them when he saw some school boys kicking a rounded boulder about. He cracked it open, and to his amazement, a perfect three-dimensionally preserved fish lay inside. After this first find, Moore collected hundreds more nodules, and the entire collection has lain, almost forgotten, in the museum of the BRLSI in Queen’s Square, Bath ever since.
Matt Williams, curator of the collection, said: “It was obvious that these fossils where very special from the first time I saw them on joining the BRLSI. Our stores are full of treasures, but these specimens are truly unique. We secured some funding to clean up the specimens, and curate them, and we even uncovered some unexpected treasures.”
Collaborator Professor Michael Benton from Bristol’s School of Earth Sciences, said: “When Matt first showed me the fossils I couldn’t believe it. There are 100 nodules containing a large fish called Pachycormus, five or six tiny marine crocodiles, and two species of ichthyosaurs. There are also early squid with their ink sacs and other soft tissues preserved, and hundreds of insects that had flown out over the shallow, warm seas of the day.”
Work will now begin in earnest on the fossils, thanks to a £250,000 grant from the Leverhulme Trust which will allow for three-dimensional scanning to be carried out and also fund young researchers to work in Bristol and Oxford with fossil fish expert, Dr Matt Friedman.
A review of the fossils is published today in the premier British geological journal, Journal of the Geological Society.
Reference:
Matt Williams, Michael J. Benton, Andrew Ross. The Strawberry Bank Lagerstätte reveals insights into Early Jurassic life. Journal of the Geological Society, 2015; 2014-144 DOI: 10.1144/jgs2014-144
Surfer is a full-function 3D visualization, contouring and surface modeling package that runs under Microsoft Windows. Surfer is used extensively for terrain modeling, bathymetric modeling, landscape visualization, surface analysis, contour mapping, watershed and 3D surface mapping, gridding, volumetrics, and much more.
Surfer’s sophisticated interpolation engine transforms your XYZ data into publication-quality maps. Surfer provides more gridding methods and more control over gridding parameters, including customized variograms, than any other software package on the market. You can also use grid files obtained from other sources, such as USGS DEM files or ESRI grid files. Display your grid as outstanding contour, 3D surface, 3D wireframe, watershed, vector, image, shaded relief, and viewshed maps. Add base maps to show boundaries and imagery, post maps to show point locations, and combine map types to create the most informative display possible. Virtually all aspects of your maps can be customized to produce exactly the presentation you want. Generating publication quality maps has never been quicker or easier.
Create colorful contour maps with custom levels, colors, and a color scale!
Contour Maps
Display contour maps over any contour range and contour interval, or specify only the contour levels you want to display on the map. And with Surfer you can add color fill between contours to produce dazzling displays of your maps, or produce gray scale fills for dramatic black and white printouts. More Info.
Create exciting 3D surface maps from your XYZ data! Image courtesy of Igor Yashayaev, Bedford Institute of Oceanography, Fisheries and Oceans, Canada
3D Surface Maps
The 3D surface map uses shading and color to emphasize your data features. Change the lighting, display angle and tilt with a click of the mouse. Overlay several surface maps to generate informative block diagrams. More Info.
Image Maps
.Surfer image maps use different colors to represent Z values of a grid file. Surfer optionally blends colors between Z values so you end up with a smooth color gradation over the entire map, or you can leave the colors unblended so each cell in the grid file shows a distinct color. Choose to display the image map with hill shading to give a 3D effect.
This powerful feature allows you to create color maps using any combination of colors. Add a color scale to show the values of the different colors! Image maps can be created independently of other maps, or can be combined with other map layers. They can be scaled, resized, limited and moved. More Info.
Post Maps
Post maps show points at XY locations, such as sample locations, well locations, or original data point locations. Use the points to show the distribution of data points on the map, and to demonstrate the accuracy of the gridding methods you use. Add multiple labels to the points, connect the points with a line, and control the size, shape and color of the symbol.
Also create classed post maps that identify different ranges of data by automatically assigning a different symbol or color to each data range. More Info.
Base Maps
Display your base maps in Surfer alone or overlay them on other maps.
Surfer can import maps in many different formats to display geographic information. Base maps are created from any number of file formats, such as SHP, DXF, GeoTIFF, and PDF. In addition to loading existing files as base map, you can also download georeferenced imagery automatically from countless free online Web Map Service (WMS) servers through Surfer’s built-in WMS browser. Connect to the online data source, pick the layer of interest you want to download, and then watch as Surfer downloads the image and seamlessly loads it into your project.
Combine base maps with other map layers in map overlays, or create stand-alone base maps independent of other maps on the page. Load any number of base maps on a page. It is easy to overlay a base map on a contour or surface wireframe map, allowing you to display geographic information in combination with the three dimensional data.
When using base map data with attribute information (such as the data in SHP files), you can manage the attribute data easily in the attribute table and query objects based on object property or attribute information. More Info.
Shaded Relief Maps
Create spectacular maps in seconds.
Shaded relief maps are raster images based on grid files. Colors are assigned based on slope orientation relative to a light source. Surfer determines the orientation of each grid cell and calculates reflectance of a point light source on the grid surface.
The light source can be thought of as the sun shining on a topographic surface. Surfer automatically blends colors between percentage values so you end up with a smooth color gradation over the map. You can add color anchors so each anchor point can be assigned a unique color, and the colors are automatically blended between adjacent anchor points. This allows you to create color maps using any combination of colors. Shaded relief maps can be created independently of other maps, or can be combined with other layers. Shaded relief maps can be scaled, resized, limited, and moved in the same way as other types of maps. More Info.
A USGS SDTS DEM file was used to create this map and color zones were defined for the X and Y lines.
3D Wireframe Maps
Surfer wireframe maps provide an impressive three dimensional display of your data. Wireframes are created by connecting Z values along lines of constant X and Y. More Info.
Vector Maps
Instantly create vector maps in Surfer to show direction and magnitude of data at points on a map. You can create vector maps from information in one grid or two separate grids. The two components of the vector map, direction and magnitude, are automatically generated from a single grid by computing the gradient of the represented surface.
At any given grid node, the direction of the arrow points in the direction of the steepest descent. The magnitude of the arrow changes depending on the steepness of the descent. Two-grid vector maps use two separate grid files to determine the vector direction and magnitude. The grids can contain Cartesian or polar data. With Cartesian data, one grid consists of X component data and the other grid consists of Y component data. With polar data, one grid consists of angle information and the other grid contains length information. Overlay vector maps on contour or wireframe maps to enhance the presentation! More Info.
Watershed Maps
Detail every aspect of your map from creating watershed boundaries to adding city streets and surrounding elevations, like the above map of Seward, Alaska.
Watershed maps automatically calculate and display drainage basins and streams from your grid file.
Create colorful watershed maps to display regions draining into a stream, stream system or body of water. Display the catchment basins, streams, or both. Export the basins and streams to any supported file format, including SHP and DXF files, for use in other software! Surfer uses the accurate eight-direction pour point algorithm to calculate the flow direction at each grid node. More Info.
Viewshed Maps
.Perform viewshed analysis using a loaded grid file with a user-specified transmitter location, height, starting angle and radius. All visible areas from the transmitter location within the selected radius are filled with a user-specified color. Alternatively, choose to display the invisible areas from the transmitter.
Viewshed analysis is useful in many applications, such as determining if mining operations or drill rigs can be viewed from public locations, determining what is visible from trails or roads, and to locate communication towers. More Info.
Profiles
Surfer’s automatic profile tool makes it easy to visualize the change in Z value from one point to another.
Simply select the map, add a profile, and draw the line on the map. Include as many points as you want in the line; it could be a simple two-point line, or a zig-zag shape. In all cases, the profile is created showing the Z value change along the length of the line. Reshape the line on the map, and the profile automatically updates. More Info.
Graticule and Grid Lines
Add graticule lines or another grid to your map to view the location in multiple sets of coordinate units! Display latitude and longitude graticule lines over a projected map, or create a map in meters and add a grid in feet. More Info.
Operation IceBridge project scientist Michael Studinger took the photo of Taylor Valley,, one of the Dry Valleys of Antarctica where snow and ice are rare. Credit: NASA
The cold permafrost of Antarctica houses bacteria that thrive at temperatures below freezing, where water is icy and nutrients are few and far between. Oligotrophs, slow-growing organisms that prefer environments where nutrients are scarce, could provide clues as to how life could exist in the permafrost of Mars.
“The slow-growing lifestyle of oligotrophs is clearly beneficial in the environment as these oligotrophs often dominate the communities in which they are found,” Corien Bakermans, assistant professor of microbiology at Penn State Altoona, told Astrobiology Magazine by email.
Bakermans was the principal investigator of a group of scientists who studied the lethargic bacteria from the Dry Valleys of Antarctica, a row of snow-free valleys that represents one of Earth’s most extreme desert environments.
“In cold, low-nutrient environments, slow growth is the law, and there are fewer fast-acting processes that disrupt that slow growth,” Bakermans said.
Permafrost is ground that remains at or below 0° C (32° F) for at least two consecutive years. The permafrost of Antarctica’s Dry Valleys house a small supply of bacteria, but the remote location makes sampling them a challenge. While permafrost exists in the more accessible Arctic regions, the Antarctic permafrost contains a higher organic count, although isn’t as well studied, Bakermans said.
Bakermans examined Taylor Valley, the southernmost of the three main valleys that make up the McMurdo Dry Valleys. Rather than focusing on the microbes that lie on the surface, her team chose to delve into the permafrost.
After setting up a clean room over the site, Bakermans’ team dug a pit roughly 20 inches (50 centimeters) square, using organic-free sterile stainless steel tools to avoid contaminating the site. They collected samples of the permafrost from a range of depths and transported them to another site where they could more easily study the microbes.
The samples they found were dominated by the phyla Acidobacteria and Gemmatimonadetes, bacteria that have not been seen in other Antarctic permafrost samples, Bakermans said. The two phyla—the second largest taxonomic rank, after kingdom—were identified as recently as 1997 and 2003, respectively.
“While these bacterial phyla are abundant in many environments, not much is known about them, given that they were only recently identified, and very few species have been successfully cultured, or grown in the lab,” said Bakermans.
Finding them in Taylor Valley wasn’t completely surprising, however.
“Many species from these phyla appear to be adapted to low-nutrient and low-water conditions, which are common in Taylor Valley,” Bakermans said. “This likely contributed to the dominance of these phyla in Taylor Valley permafrost.”
Scientists can study the genetic makeup of bacteria to track their relationships among various species. The team extracted two specific genes from bacteria in the permafrost and placed them into clones to characterize the challenging bacteria.
“All bacteria contain at least one copy of each of these genes, but very often we cannot grow these bacteria in the lab to examine them,” Bakermans said.
“By transferring the genes from the permafrost bacterium to the clone, which can be grown in the laboratory, we can now examine the genes.”
By changing the environment and monitoring production of carbon dioxide—the respiration of the organisms—the scientists were able to understand how various environments affected the bacteria. Samples were started at very low temperatures of -20° C (-4° F) and then incubated at a variety of higher temperatures to determine where they thrived. They found that activity occurred as low as -5° C (23° F) and peaked at 15° C (59° F).
The research was published in the journal FEMS Microbiology Ecology and was funded by the NASA Astrobiology Science and Technology for Exploring Planets program.
‘How life survives’
The Dry Valleys of Antarctica serve as a proving ground for how life can endure in inhospitable environments, such as the arid regions of Mars. The valleys are cold and dry, though they don’t reach Martian extremes, where the temperatures average about -80° F (-60° C). Their permafrost is similar to the permafrost and ground ice found in the middle to high latitudes of Mars.
While evolution on other planets may not follow the exact same track, studying bacteria that survive and thrive in the most inhospitable regions on Earth can provide some insight into what it might take for alien organisms to endure elsewhere.
“These valleys are important for understanding how life survives in extreme cold and dry,” astrobiologist Chris McKay of NASA Ames Research Center told Astrobiology Magazine by email.
McKay was one of the co-authors on Bakermans’ study. He specializes in valleys drier and higher than Taylor Valley in permafrost that contains less liquid, making it compositionally more similar to Martian soil, where only ice and vapor form rather than liquid water.
Low in humidity, the Dry Valleys don’t have a lot of water, the ingredient required for life as we know it. Despite their Antarctic locale, the valleys lack snow and ice, forming the largest ice-free region on the continent.
The Dry Valleys can serve as a window into finding evidence for past life on Mars, as scientists scouring the regions find traces of previous generations as well as thriving organisms.
“They help us understand how evidence for life in the form of dead microorganisms is preserved under these conditions,” McKay said.
Note: The above post is reprinted from materials provided by Astrobio.net. This story is republished courtesy of NASA’s Astrobiology Magazine. Explore the Earth and beyond at www.astrobio.net .
Georgia Tech postdoctoral fellow Jay Forsythe loads a sample into a mass spectrometer. The testing was done to see what compounds were formed by subjecting mixtures of amino and hydroxy acids to repeated wet-dry cycles. Credit: John Toon, Georgia Tech
Anyone who’s ever noticed a water puddle drying in the sun has seen an environment that may have driven the type of chemical reactions that scientists believe were critical to the formation of life on the early Earth.
Research reported July 15 in the journal Angewandte Chemie International Edition demonstrates that important molecules of contemporary life, known as polypeptides, can be formed simply by mixing amino and hydroxy acids – which are believed to have existed together on the early Earth – then subjecting them to cycles of wet and dry conditions. This simple process, which could have taken place in a puddle drying out in the sun and then reforming with the next rain, works because chemical bonds formed by one compound make bonds easier to form with the other.
The research supports the theory that life could have begun on dry land, perhaps even in the desert, where cycles of nighttime cooling and dew formation are followed by daytime heating and evaporation. Just 20 of these day-night, wet-dry cycles were needed to form a complex mixture of polypeptides in the lab. The process also allowed the breakdown and reassembly of the organic materials to form random sequences that could have led to the formation of the polypeptide chains that were needed for life.
“The simplicity of using hydration-dehydration cycles to drive the kind of chemistry you need for life is really appealing,” said Nicholas Hud, a professor in the School of Chemistry and Biochemistry at the Georgia Institute of Technology, and director of the NSF Center for Chemical Evolution, which is also supported by the NASA Astrobiology Program. “It looks like dry land would have provided a very favorable environment for getting the chemistry necessary for life started.”
Origin-of-life scientists had previously made polypeptides from amino acids by heating them well past the boiling point of water, or by driving polymerization with activating chemicals. But the high temperatures are beyond the point at which most life could survive, and the robust availability of activating chemicals on the early Earth is questionable. The simplicity of the wet-dry cycle therefore makes it attractive to explain how peptides could have formed, Hud added.
The idea for combining chemically similar amino acids and hydroxyl acids was inspired by the demonstration that polyesters are easy to form by repetitive hydration-dehydration cycles and the fact that esters are activated to attack by the amino group of amino acids. The potential importance of this reaction in the earliest stages of life is supported by studies of meteorites, which revealed that both compounds would have been present on the prebiotic Earth.
Hydroxy acids combine to form polyester, better known as a synthetic textile fiber, and that reaction requires less energy than formation of the amide bonds needed to create peptides from amino acids. In the wet-dry cycles, formation of polyester comes first – which then facilitates the more difficult peptide formation, Hud said.
“The ester linkages that we are making in the polyester can serve as an activating agent formed within the solution,” he explained. “Over the course of a very simple chemical evolution, the polymers progress from having hydroxy acids with ester linkages to amino acids with peptide linkages. The hydroxy acids are gradually replaced through the wet and dry cycles because the ester bonds holding them together are not as stable as the peptide bonds.”
Experimentally, graduate student Sheng-Sheng Yu put the amino and hydroxy acid mixtures through 20 wet-dry cycles to produce molecules that are a mixture of polyesters and peptides, containing as many as 14 units. After just three cycles, and at temperatures as low as 65 degrees Celsius, peptides consisting of two and three units began to form. Postdoctoral fellow Jay Forsythe confirmed the chemical structures using NMR mass spectrometry.
“We allowed the peptide bonds to form because the ester bonds lowered the energy barrier that needed to be crossed,” Hud added.
On the early Earth, those cycles could have taken 20 days and nights – or perhaps much longer if the heating and drying cycles corresponded to seasons of the year.
Beyond easily forming the polypeptides, the wet-dry process has an additional advantage. It allows compounds like peptides to be regularly broken apart and reformed, creating new structures with randomly-ordered amino acids. This ability to recycle the amino acids not only conserves organic material that may have been in short supply on the early Earth, but also provides the potential for creating more useful combinations.
A combination of hydroxy and amino acids likely existed in the prebiotic soup of the early Earth, but analyzing such a “messy” reaction was challenging, Hud said. “We were led into this idea that a mixture might work better than separate components,” he explained. “It might have been messy at the start, but it’s easier to get going than a pristine chemical reaction.”
Beyond helping explain how life might have started, the wet-dry cycles could also provide a new way to synthesize polypeptides. Existing techniques produce the chemicals through genetic engineering of microorganisms, or through synthetic organic chemistry. The wet-dry cycling could provide a simpler and more sustainable water-based process for producing these chemicals.
The demonstration of peptide formation opens the door to asking other questions about how life may have gotten going in prebiotic times, said Ramanarayanan Krishnamurthy, a member of the research team and an associate professor of chemistry at the Scripps Research Institute. Future studies will include a look at the sequences formed, whether there are sequences favored by the process, and what sequences might result. The process could ultimately lead to reactions able to continue without the wet-dry cycles.
“If this process were repeated many times, you could grow up a peptide that could acquire a catalytic property because it had reached a certain size and could fold in a certain way,” Krishnamurthy said. “The system could begin to develop certain emergent characteristics and properties that might allow it to self-propagate.”
Of the more than 1,000 verified planets found by NASA’s Kepler Space Telescope, eight are less than twice Earth-size and in their stars’ habitable zone. Credit: NASA
Planet Earth is situated in what astronomers call the Goldilocks Zone — a sweet spot in a solar system where a planet’s surface temperature is neither too hot nor too cold. An ideal distance from a home star — in Earth’s case, the sun – this habitable zone, as it is also known, creates optimal conditions that prevent water from freezing and generating a global icehouse or evaporating into space and creating a runaway greenhouse.
However, a new theory by UC Santa Barbara geochemist Matthew Jackson posits that the bulk composition of a planet may also play a critical role in determining the planet’s tectonic and climatic regimes and therefore its habitability. In a paper published today in Nature Geoscience, Jackson, an associate professor in UCSB’s Department of Earth Science, and Mark Jellinek of the University of British Columbia discuss their research.
According to Jackson, plate tectonics is a manifestation of the Earth trying to cool itself. Cold plates sink into the Earth and absorb heat, while volcanoes release heat where plates are spreading apart and forming. “Whether or not plate tectonics can happen actually depends on whether or not the Earth is too hot or too cold,” he said. “If it’s too hot, plate tectonics seizes up and if it’s too cold, it freezes up.”
Until a decade ago, Jackson noted, scientists based the Earth’s composition on a model tied to ancient stony meteorites called chondrites, which were considered the building blocks of the planet. Then studies analyzing the ratio of two neodymium isotopes — 142Nd and 144Nd — demonstrated that Earth’s composition may differ from that of chondrites — and differ enough to send scientists back to the drawing board.
In 2013, Jackson and Jellinek published a new compositional model of the Earth in which a large portion of the mantle was depleted to form the continental crust. The model also assumed a 30 percent reduction in the uranium, thorium and potassium content in the planet. The decay of these naturally occurring elements generates almost all of the planet’s radioactive heat.
The new paper takes this revised model further by examining Earth’s geodynamics. “We argue that if the planet had as much uranium, thorium and potassium as the old model, plate tectonics might not be possible,” explained Jackson. “If this is the case, you can end up with a planet that has only one big plate and can become an extreme greenhouse like Venus. The new compositional model gives Earth a sweet spot of its own where its interior is neither too hot nor too cold — a place that allows our current mode of plate tectonics to operate.”
Jackson added that the thermal and tectonic histories of the Earth are intimately intertwined, and this latest paper explores what happens if heat production is turned down by a third, as the new compositional model suggests.
If uranium, thorium and potassium govern whether or not plate tectonics can occur, as Jackson and Jellinek propose, astronomers looking for habitable planets might have another parameter to consider. Since NASA’s Kepler Space Telescope has already found more than 1,000 planets — a small fraction of which reside in the habitable zone around their respective stars — it is important to understand how additional variables, including a planet’s composition, can narrow the field of potentially habitable extrasolar worlds.
“Our hypothesis suggests that among the rocky exoplanets, there’s another dial that’s important to turn when considering whether a planet is habitable or not: its bulk composition,” Jackson said. “Bulk composition determines its uranium, thorium and potassium abundance, which governs its internal radiogenic heating and ultimately dictates whether or not plate tectonics can happen — as well as the amount of volcanism and the release of CO2 from a planet that can occur. These are the variables that determine whether a planet can support a habitable climate.”
Living Rock – An Introduction to Earth’s Geology movie was released Aug 13, 2002 by the DVD International studio. Ever wonder why earthquakes happen, or how a volcano works? Living Rock – An Introduction to Earth’s Geology movie Find the answers to these and many other questions in LIVING ROCK, a fun and educational program about the Earth’s geology, jointly produced by the US Geological Survey and Alpha DVD.
Living Rock – An Introduction to Earth’s Geology video Introduces concepts such as Geologic Time, Continental Crust, Plate Tectonics, Volcanic Activity, Earthquakes, Subduction Zones, Erosion, and Glaciers.
A seminal discovery. Credit: Department of Palaeobiology, Swedish Museum of Natural History
From trilobites to tyrannosaurs, most fossils are of creatures with hard shells or bones. These materials don’t easily biodegrade and sediment has time to build up around them and turn them into a record of the creature that is still with us millions of years after it has died. Soft-bodied organisms like worms, on the other hand, decay rapidly and their fossil record is decidedly patchy.
In exceptional circumstances, however, their remains are preserved and sometimes in the most unusual places. With the right detective skills, palaeontologists can use such discoveries to open up whole new windows on the history of life on Earth. A recent discovery found in 50-million-year-old rocks from Antarctica has yielded a particularly incredible example: fossilised worm sperm.
It’s a great reminder that there are far stranger fossils out there than dinosaur bones. Here are some of the most bizarre specimens ever found.
A seminal discovery. Credit: Department of Palaeobiology, Swedish Museum of Natural History
This remarkable find of fossilised spermatozoa from a clitellate or “collared” worm represents the oldest animal sperm ever discovered, beating the previous record holder – springtail sperm found in Baltic amber – by at least ten million years.
The sperm preservation was made possible because such worms reproduce by releasing their eggs and sperm into protective cocoons. In this case, a tough shell kept the cocoons intact until scientists discovered them in shallow marine gravels on the Antarctic Peninsula. Even then, it required high-powered microscopic analysis for the sperm to be spotted.
The sperm most resemble those of a leech-like group of worms that attach themselves to crayfish, even though today these live only in the northern hemisphere. But the researchers think the technique could be applied to other cocoon fossils, and help us learn more about previously cryptic creatures.
2. A well-endowed Silurian shrimp
If 50-million-year-old spermatozoa are surprising, what about a 425-million-year-old penis? Discovered in a ditch near the Anglo-Welsh border in the early 2000s, a tiny ostracod, or seed shrimp, proved to be quite clearly male. Preserved in three-dimensions with all its soft tissues fossilised, it was proportionally well-endowed. “Old Todger” was the headline in the The Sun newspaper.
During the Silurian period (443-419 million years ago), the Welsh borderlands lay on the shelf of a tropical sea. Marine animals were occasionally smothered, entombed and petrified by the ash of distant volcanoes. The ostracod – and countless other small fossils – cannot be seen adequately using microscopes, however, so their mineral tomb has to be gradually ground away and the fossil recreated with 3D digital imaging.
3. Ancient reptile poo and puke
Credit: Poozeum/Wikimedia Commons, CC BY-SA
The notion that where there’s muck there’s brass is perhaps best shown by coprolites: petrified dung that can be found in many palaeontological shops. Beyond the novelty, such specimens are “trace fossils” of tremendous palaeoecological value. This means they can tell scientists precisely what an extinct creature was eating.
Coprolites are actually just one element of a richer broth, that of bromalites or “stink rocks”. The term was coined in the early 1990s to encompass all matter of excreta preserved in the rock record, and in the last few years, bromalites have been popping up everywhere.
In Australia, they show that Cretaceous plesiosaurs were bottom feeders. In Poland the regurgitated dinners of shell-crushing fish help us work out how life recovered from the biggest mass extinction in Earth history. And in Jurassic shales from Peterborough and Whitby, pavements of squid-like belemnites have been interpreted as ichthyosaur vomit.
4. Yorkshire rhinos
Buckland in the hyaena’s cave
One very odd fossil discovery was made in Kirkdale Cave, near Kirkbymoorside, North Yorkshire in 1821. Workman quarrying for roadstone found a cliffside hollow full of large animal bones. They were at first thought to be cattle, but a local naturalist saw that they were more exotic-looking, and the remains eventually made their way to Oxford University’s Professor William Buckland.
A man who claimed to have eaten his way through the entire animal kingdom, Buckland was the most marvellous experimental scientist. He recognised that the bones were mainly of large herbivores, such as elephants and rhinos. They showed signs of having been gnawed, and fossilised faeces found on the cave floor resembled those of hyaenas. Conveniently being in possession of one as a pet, Buckland proved Kirkdale Cave had been a hyaena den, and founded the science of palaeoecology. Almost two hundred years on, we know that “African” megafauna roamed the Vale of Pickering about 125,000 years ago, in a warm phase between ice ages.
5. A mystery monster
Credit: Ghedoghedo/Wikimedia Commons, CC BY-SA
The fossils of Mazon Creek in Illinois, USA, were first encountered during coal mining in the 19th Century. But it wasn’t until the 1950s that the site became fossiliferously famous, thanks to Francis Tully’s discovery of an exceptionally weird beast: a beautifully preserved soft-bodied animal revealed in a naturally split mineral nodule.
Specimens turned out to be quite abundant but unique to Mazon Creek, and the beast was given the name of Tullimonstrum gregarium. It is now the state fossil of Illinois. Trouble is, no-one knows what Mr Tully’s Common Monster really is. A few inches long, it has a long snout with toothy pincers at the end, two eyes on stalks, a segmented body, and a finned tail. It was probably a predator, and the rocks it was found in suggest that it lived in tropical, shallow seas.
Beyond that, after more than half a century, we’re not much the wiser. It cannot be satisfactorily united with any other invertebrate group, living or extinct. Even with exceptional preservation, the fossil record always has the capacity to surprise.
Note: The above post is reprinted from materials provided by The Conversation. This story is published courtesy of The Conversation (under Creative Commons-Attribution/No derivatives).The Conversation
Topographic relief map of the northern Santorini volcanic field. The white star icon shows the location of the Kallisti Limnes CO2 pools. The onshore Kolumbo fault is indicated by a dashed red line, which along with the Kolumbo line, describes the northeast portion of the Christianna-Santorini-Kolumbo (CSK) tectonic line. The inset box shows a detailed view from the southwest of the caldera slope bathymetry around the study site; submersible vehicle track lines are indicated as red, orange, and yellow lines, corresponding to the first and second AUV dives, and the HOV dive, respectively. Credit: Illustration courtesy of Camilli, et al
The location of the second largest volcanic eruption in human history, the waters off Greece’s Santorini are the site of newly discovered opalescent pools forming at 250 meters depth. The interconnected series of meandering, iridescent white pools contain high concentrations of carbon dioxide (CO2) and may hold answers to questions related to deepsea carbon storage as well as provide a means of monitoring the volcano for future eruptions.
“The volcanic eruption at Santorini in 1600 B.C. wiped out the Minoan civilization living along the Aegean Sea,” said Woods Hole Oceanographic Institution (WHOI) scientist Rich Camilli, lead author of a new study published today in the journal Scientific Reports. “Now these never-before-seen pools in the volcano’s crater may help our civilization answer important questions about how carbon dioxide behaves in the ocean.”
Camilli and his colleagues from the University of Girona, National and Kapodistrian University of Athens, Institut de Physique du Globe de Paris, and Hellenic Centre for Marine Research (HCMR), working in the region in July 2012, used a series of sophisticated underwater exploration vehicles to locate and characterize the pools, which they call the Kallisti Limnes, from ancient Greek for “most beautiful lakes.” A prior volcanic crisis in 2011 had led the researchers to initiate their investigation at a site of known hydrothermal activity within the Santorini caldera. During a preliminary reconnaissance of a large seafloor fault the University of Girona’s autonomous underwater vehicle (AUV) Girona 500 identified subsea layers of water with unusual chemical properties.
Following the AUV survey, the researchers then deployed HCMR’s Thetis human occupied vehicle. The submersible’s crew used robotic onboard chemical sensors to track the faint water column chemical signature up along the caldera wall where they discovered the pools within localized depressions of the caldera wall. Finally, the researchers sent a smaller remotely operated vehicle (ROV), to sample the pools’ hydrothermal fluids.
“We’ve seen pools within the ocean before, but they’ve always been brine pools where dissolved salt released from geologic formations below the seafloor creates the extra density and separates the brine pool from the surrounding seawater,” said Camilli. “In this case, the pools’ increased density isn’t driven by salt – we believe it may be the CO2 itself that makes the water denser and causes it to pool.”
Where is this CO2 coming from? The volcanic complex of Santorini is the most active part of the Hellenic Volcanic Arc. The region is characterized by earthquakes caused by the subduction of the African tectonic plate underneath the Eurasian plate. During subduction, CO2 can be released by magma degassing, or from sedimentary materials such as limestone which undergo alteration while being subjected to enormous pressure and temperature.
The researchers determined that the pools have a very low pH, making them quite acidic, and therefore, devoid of calcifying organisms. But, they believe, silica-based organisms could be the source of the opal in the pool fluids.
Until the discovery of these CO2-dense pools, the assumption has been that when CO2 is released into the ocean, it disperses into the surrounding water. “But what we have here,” says Camilli, “is like a ‘black and tan’ – think Guinness and Bass – where the two fluids actually remain separate” with the denser CO2 water sinking to form the pool.
The discovery has implications for the build up of CO2 in other areas with limited circulation, including the nearby Kolumbo underwater volcano, which is completely enclosed. “Our finding suggests the CO2 may collect in the deepest regions of the crater. It would be interesting to see,” Camilli said, adding it does have implications for carbon capture and storage.
Sub-seafloor storage is gaining acceptance as a means of reducing heat-trapping CO2 in the atmosphere and lessening the acidifying impacts of CO2 in the ocean. But before fully embracing the concept, society needs to understand the risks involved in the event of release.
Temperature sensors installed by the team revealed that the Kallisti Limnes were 5°C above that of surrounding waters. According to co-author Javier Escartin, “this heat is likely the result of hydrothermal fluid circulation within the crust and above a deeper heat source, such as a magma chamber.” These temperatures may provide a useful gauge to study the evolution of the system. Escartin added that “temperature records of hydrothermal fluids can show variations in heat sources at depth such as melt influx to the magma chamber. The pool fluids also respond to variations in pressure, such as tides, and this informs us of the permeability structure of the sub-seafloor.” Changes in the pools’ temperature and chemical signals may thus complement other monitoring techniques as useful indicators of increased or decreased volcanism.
This European – American research collaboration was funded through support from the EU Eurofleets program, Institut de Physique du Globe de Paris, Hellenic Centre for Marine Research, the US National Science Foundation, and NASA’s astrobiology program (ASTEP) which supports autonomous technology development to search for life on other planets. “From a technology perspective, it was a big step forward,” Camilli said.
Research led by Oxford University scientists shows that mammals were evolving up to ten times faster in the middle of the Jurassic than they were at the end of the period. An illustration showing docodonts, now extinct mammals that saw an explosion of skeletal and dental changes (including the special molar teeth that give them their name), in the Middle Jurassic. Credit: April Neander
Mammals were evolving up to ten times faster in the middle of the Jurassic than they were at the end of the period, coinciding with an explosion of new adaptations, new research shows.
Early mammals lived alongside the dinosaurs during the Mesozoic era (252-66 million years ago). They were once thought to be exclusively small nocturnal insect-eaters, but fossil discoveries of the past decade — particularly from China and South America — have shown that they developed diverse adaptations for feeding and locomotion, including gliding, digging, and swimming.
To find out when and how rapidly these new body shapes emerged a team led by Oxford University researchers did the first large-scale analysis of skeletal and dental changes in Mesozoic mammals. By calculating evolutionary rates across the entire Mesozoic, they show that mammals underwent a rapid ‘burst’ of evolutionary change that reached its peak around the middle of the Jurassic (200-145 million years ago).
The team comprised researchers from Oxford University in the UK and Macquarie University in Australia. A report of the research is published in Current Biology.
‘What our study suggests is that mammal ‘experimentation’ with different body-plans and tooth types peaked in the mid-Jurassic,’ said Dr Roger Close of Oxford University’s Department of Earth Sciences, lead author of the report. ‘This period of radical change produced characteristic body shapes that remained recognisable for tens of millions of years.’
The team recorded the number of significant changes to body plans or teeth that occurred in mammal lineages every million years. During the mid-Jurassic the frequency of such changes increased to up to 8 changes per million years per lineage, almost ten times that seen at the end of the period. This is exemplified by therian mammals, the lineage leading to placental mammals and marsupials, which were evolving 13 times faster than average in the mid-Jurassic, but which had slowed to a rate much lower than average by the later Jurassic. This ‘slow-down’ occurred despite the increase in the number of mammal species seen in this later period.
‘We don’t know what instigated this evolutionary burst. It could be due to environmental change, or perhaps mammals had acquired a ‘critical mass’ of ‘key innovations’ — such as live birth, hot bloodedness, and fur — that enabled them to thrive in different habitats and diversify ecologically,’ said Dr Close. ‘Once high ecological diversity had evolved, the pace of innovation slowed.’
Multituberculates, for instance, saw radical changes to their skeletons and teeth during the mid-Jurassic. However, by the end of the period they had evolved their rodent-like body shape and distinctive teeth, a form that, despite diversifying into hundreds of different species, they would generally retain until they went extinct around 130 million years later.
‘This is characteristic of other ‘adaptive radiation’ events of this kind, such as the famous ‘Cambrian explosion’,’ said Dr Close. ‘In the Jurassic we see a profusion of weird and wonderful bodies suddenly appear and these are then ‘winnowed down’ so that only the most successful survive. What we may have identified in this study is mammals’ own ‘Cambrian explosion’ moment, when evolutionary experimentation ran wild and the future shape of mammals was up for grabs.’
Reference:
Roger A. Close, Matt Friedman, Graeme T. Lloyd, Roger B.j. Benson. Evidence for a Mid-Jurassic Adaptive Radiation in Mammals. Current Biology, 2015 DOI: 10.1016/j.cub.2015.06.047
