This image shows a swim traceway from Capitol Reef National Park. Credit: Tracy J. Thomson and Mary L. Droser, Geology, 5 Feb. 2015.
Vertebrate tracks provide valuable information about animal behavior and environments. Swim tracks are a unique type of vertebrate track because they are produced underwater by buoyant trackmakers, and specific factors are required for their production and subsequent preservation. Early Triassic deposits contain the highest number of fossil swim track occurrences worldwide compared to other epochs, and this number becomes even greater when epoch duration and rock outcrop area are taken into account.
This spike in swim track occurrences suggests that during the Early Triassic, factors promoting swim track production and preservation were more common than at any other time. Coincidentally, the Early Triassic period follows the largest mass extinction event in Earth’s history, and the fossil record indicates that a prolonged period of delayed recovery persisted throughout this time period.
During this recovery interval, sediment mixing by animals living within the substrate was minimal, especially in particularly stressful environments such as marine deltas. The general lack of sediment mixing during the Early Triassic was the most important contributing factor to the widespread production of firm-ground substrates ideal for recording and preserving subaqueous trace fossils like swim tracks.
Reference:
T. J. Thomson, M. L. Droser. Swimming reptiles make their mark in the Early Triassic: Delayed ecologic recovery increased the preservation potential of vertebrate swim tracks. Geology, 2015; DOI: 10.1130/G36332.1
Abundant stalagmites, stalactites and columns in Yok Balum Cave, Belize. Dr. Harriet Ridley is visible in the centre of the photo, and Dr. Keith Prufer is visible to the right. Credit: Dr. James Baldini, Durham University
Scientists have produced a rainfall record strongly suggesting that man-made industrial emissions have contributed to less rainfall in the northern tropics.
The research team, led by experts at Durham University, UK, reconstructed rainfall patterns stretching back more than 450 years by analysing the chemical composition of a stalagmite recovered from a cave in Belize, Central America.
They identified a substantial drying trend from 1850 onwards, coinciding with a steady rise in sulphate aerosols in the atmosphere as a result of burning fossil fuels to drive the industrial boom in Europe and North America.
Importantly they also identified nine short-lived drier spells in the northern tropics since 1550 following very large volcanic eruptions in the Northern Hemisphere that produced similar emissions as those produced by burning fossil fuels.
This provided very strong evidence that any injection of sulphate aerosols into the upper atmosphere could lead to shifts in rainfall patterns, the researchers said.
Writing in the journal Nature Geoscience the researchers said that sulphate aerosols moderated temperatures in the Northern Hemisphere by reflecting the Sun’s radiation.
As a result the Intertropical Convergence Zone (ITCZ) – a tropical rainfall belt near the equator – shifted towards the warmer Southern Hemisphere leading to dryer conditions in the northern tropics.
The findings confirm previously published observations using 20th Century historical data and computer modelling, the researchers said.
Lead author Dr Harriet Ridley, from the Department of Earth Sciences at Durham University, said: “The research presents strong evidence that industrial sulphate emissions have shifted this important rainfall belt, particularly over the last 100 years.
“Although warming due to man-made carbon dioxide emissions has been of global importance, the shifting of rain belts due to aerosol emissions is locally critical, as many regions of the world depend on this seasonal rainfall for agriculture.
“The role of sulphate aerosols in repositioning the ITCZ was previously identified using computer modelling, but until now no suitable climate record existed to support those ideas.
“Our research allows us to make more accurate predictions about future climate trends and it appears that regional sulphate aerosol production is an essential factor to include in these predictions.”
The researchers said their interpretations were made possible because of the quality of the stalagmite sample they obtained from the Yok Balum cave in Belize, which is located at the northernmost extent of the modern day ITCZ and is sensitive to changes in its position.
By analysing the isotope values of the stalagmite – where more negative values equal wet conditions and less negative values equal dry conditions – they were able to reconstruct rainfall.
Co-author Dr James Baldini, of the Department of Earth Sciences, at Durham University, said: “The stalagmite was composed entirely of mineral aragonite, and subtle changes in the chemistry of the mineral were linked to rainfall variability. The stalagmite grew remarkably quickly and was easily dated.
“The fact that tropical drying follows both Northern Hemisphere volcanic and industrial sulphate injections is critical. It essentially rules out the possibility that the climate shifts were caused by a previously unknown natural climate cycle or increasing atmospheric carbon dioxide concentrations.”
The Durham-led research team also included researchers from the University of New Mexico, Pennsylvania State University, SUNY Stony Brook, Northern Arizona University, ETH Zurich, and the Potsdam Institute for Climate Impact Research.
The work was funded by the European Research Council, the National Science Foundation of the United States, the Alphawood Foundation and the Schweizer National Fund, Sinergia.
Reference:
Aerosol forcing of the position of the intertropical convergence zone since AD 1550, Ridley, HE, et al, Nature Geoscience, DOI: 10:1038/NGEO2353
Fig.2 Paratype (IVPP V 19972) and reconstruction of Panxianichthys imparilis (Image by XU Guanghui)
The Ionoscopiformes are a fossil fish lineage of halecomorphs known only from the Mesozoic marine deposits. Because of their close relationships with the Amiiformes, the Ionoscopiformes are phylogenetically important in investigating the early evolution and biogeography of the Halecomorphi, but fossil evidence of early ionoscopiforms was scarce. Robustichthys recently reported from the Middle Triassic Luoping Biota, eastern Yunnan, China, represents the oldest and only known ionoscopiform in the Triassic.
In a paper published in the latest issue of Vertebrata PalAsiatica, Dr. XU Guanghui, Institute of Vertebrate Paleontology and Paleoanthropology (IVPP) of the Chinese Academy of Sciences, and his colleague reported the discovery of a new ionoscopiform, Panxianichthys imparilis, on the basis of two well preserved specimens from the Middle Triassicof the Guanling Formation exposed in Xinmin of Panxian County, western Guizhou, China. Although Panxianichthys is slightly younger than Robustichthys, it is significantly older than other members of this group from the Late Jurassic of Europe, and Early Cretaceous of North and South America.
Fig.1 Holotype of Panxianichthys imparilis (IVPP V 19971) (Image by XU Guanghui)
Panxianichthys possesses an important synapomorphy of the Ionoscopiformes: a sensory canal in the maxilla, but retains some primitive characters unknown in other ionoscopiforms. It is distinguished from other members of this order by a combination of features.
Phylogenetic analysis indicates that Panxianichthys is the most primitive ionoscopiform fish, and provides new insight on the early evolution of this clade. The new finding extends the geographical distribution of early ionoscopiforms from eastern Yunnan into western Guizhou, demonstrating a wider distribution than previously appreciated for this group. The successive discoveries of Robustichthys and Panxianichthys from China indicate that the early diversification of the Ionoscopiformes is more rapid than previously thought.
This research was mainly supported by the National Natural Science Foundation of China, and the State Key Laboratory of Palaeobiology and Stratigraphy (Nanjing Institute of Geology and Palaeontology, Chinese Academy of Sciences).
Figure 1 is a Location map. (A) Key tectonic elements of the Pacific-Australian plate boundary, including the Alpine fault through the continental South Island of New Zealand. Topography is after Sandwell and Smith (1997). White box illustrates location of B. (B) More detailed map of the Alpine fault (red line), illustrating locations mentioned in the text. Orange lines are roads; gray lines are topographic contours. (C) Composite schematic section through a typical Alpine fault oblique thrust segment, illustrating the sequence of fault rocks exposed in the hanging wall, modified after Norris and Cooper (2007). Outcrops at Stoney Creek, Hare Mare Creek/Waikukupa River, and Havelock Creek are particularly characteristic. DFDP–Deep Fault Drilling Project. Credit: V. Toy et al., and Lithosphere
Rocks within plate boundary scale fault zones become fragmented and altered over the earthquake cycle. They both record and influence the earthquake process. In this new open-access study published in Lithosphere on 4 Feb., Virginia Toy and colleagues document fault rocks surrounding New Zealand’s active Alpine Fault, which has very high probability of generating a magnitude 8 or greater earthquake in the near future.
Descriptions already suggest that the complex fault rock sequence results from slip at varying rates during multiple past earthquakes, and even sometimes during aseismic slip. They also characterize this fault before rupture; Toy and colleagues anticipate that repeat observations after the next event will provide a previously undescribed link between changes in fault rocks and the ground shaking response. They write that in the future this sort of data might allow realistic ground shaking predictions based on observations of other “dormant” faults.
Reference:
Fault rock lithologies and architecture of the central Alpine Fault, New Zealand, revealed by DFDP-1 drilling
V.G. Toy et al., University of Otago, Dunedin, New Zealand. Published online ahead of print on 4 Feb. 2015; http://dx.doi.org/10.1130/L395.1. This article is OPEN ACCESS.
Artist’s impression of Josephoartigasia monesi. Credit: James Gurney
The largest rodent ever to have lived may have used its front teeth just like an elephant uses its tusks, a new study led by scientists at the University of York and The Hull York Medical School (HYMS) has found.
Josephoartigasia monesi, a rodent closely related to guinea pigs, lived in South America approximately 3 million years ago. It is the largest fossil rodent ever found, with an estimated body mass of 1000 kg and was similar in size to a buffalo.
Dr Philip Cox, of the Centre for Anatomical and Human Sciences, a joint research centre of the University’s Department of Archaeology and HYMS, used computer modelling to estimate how powerful the bite of Josephoartigasia could be.
He found that, although the bite forces were very large – around 1400 N, similar to that of a tiger – the incisors would have been able to withstand almost three times that force, based on earlier estimates by co-authors, Dr Andres Rinderknecht, of The Museo Nacional de Historia Natural, Montevideo, and Dr Ernesto Blanco, of Facultad de Ciencias, Instituto de Fısica, Montevideo, who first described the fossil in 2008.
Dr Cox said: “We concluded that Josephoartigasia must have used its incisors for activities other than biting, such as digging in the ground for food, or defending itself from predators. This is very similar to how a modern day elephant uses its tusks.”
The research, which is published in the Journal of Anatomy, involved CT scanning the Josephoartigasia monesi specimen and making a virtual reconstruction of its skull. This was then subjected to finite element analysis, an engineering technique that predicts stress and strain in a complex geometric object.
Reference:
Philip G. Cox, Andrés Rinderknecht, R. Ernesto Blanco. Predicting bite force and cranial biomechanics in the largest fossil rodent using finite element analysis. Journal of Anatomy, 2015; DOI: 10.1111/joa.12282
Melting glaciers lead to higher sea levels and a thinner oceanic crust. Credit: Duane Miller/Getty
The Earth’s ice ages have left their mark on the thickness of the planet’s oceanic crust, scientists have discovered. During glacial periods, when sea levels are low, the magma that spreads out from mid-ocean ridges to form virgin crust wells up thick and fast. But the production of new crust is stunted in warmer times when sea levels are high, such as they are today.
“We know that volcanism has an effect on climate. What we’re seeing is that climate cycles are also affecting ocean volcanism,” says Richard Katz, a geophysicist at the University of Oxford, UK, and one of the authors of the study, which is reported today in Science.
The researchers say that they have spotted the effect in chains of hillocks under the sea between Australia and the Antarctic. The reason, Katz explains, is that higher sea levels exert a greater pressure on Earth’s mantle below the ocean floor. This seems to slow the transport of molten rock and gas from the mantle up to mid-ocean ridges, where it erupts.
Periodic variations in Earth’s axial tilt and orbit around the Sun have driven the planet’s succession of ice ages and warm periods over the past two million years. During an ice age, more water is trapped on land; as a result, sea levels are more than 100 metres lower than in warm periods. And that can thicken the oceanic crust by around 800 metres (on the order of 10%), Katz says.
Anthropogenic climate change will not impose much extra variation on this pattern. Today’s sea levels are already high, geologically speaking. And scientists will have to hang around for quite a while to spot the effects of modern sea-level rise in the oceanic crust: because magma creeps slowly up from Earth’s interior to the surface, the lag between a change in sea level and the peak crustal thickness response might be about 50,000 years.
A tale of high seas
Scientists knew that changes in the pressure of ice sheets affect what happens in Earth’s upper mantle below land masses. For example, the disappearance of ice is thought to have strongly increased mantle melting and volcanism beneath Iceland. But many geologists were doubtful about whether sea-level variations alone could produce similar effects beneath ridge zones in the deep ocean.
Yet Katz and his colleagues calculated that sea-level variation should sometimes have a discernible effect on the thickness of oceanic crust spreading from ridge zones. The effect is complicated: it depends on the level of the sea, the rate at which this level rises or falls, the rate at which magma upwells from the mantle, and the rate at which oceanic crust spreads sideways from mid-ocean ridges.
The team then backed up its hypothesis by examining two areas of a mid-oceanic ridge between Australia and the Antarctic, which had been surveyed in 2011 and 2013 by the Korean icebreaker Araon. There, the sea floor is lined by elongated chains of hills around 200 metres high. (The change in oceanic crust thickness needed to produce the hills is up to about 800 metres, says Katz; much of the crust is submerged into the mantle, rather as the bulk of a floating iceberg sits under water).
The hills have been formed by a mixture of seismic activity, sedimentation, volcanoes and sea-floor spreading. But the researchers say that in the geological fabric there seems to be a distinct pattern of crustal-thickness variations that are synchronized with 23,000-, 41,000- and 100,000-year glacial cycles known as Milankovitch cycles.
“This is a fascinating discovery and an important key to understanding the creation of oceanic crust,” says Ken Macdonald, a geologist at the University of California, Santa Barbara, who was not involved in the study.
“It’s very convincing, because they actually work through the physics,” says Carl Wunsch, an oceanographer at the Massachusetts Institute of Technology in Cambridge.
A second paper, published today in Geophysical Research Letters, comes to similar conclusions. Maya Tolstoy, a geophysicist at Columbia University in New York, found that volcanic activity along the East Pacific Rise, an ocean ridge off the coast of Mexico, ebbs and flows in regular cycles. Among other shorter cycles, she found on the fast-spreading sea floor in that region a 100,000-year pattern strikingly in synch with the most prominent of Earth’s natural glacial cycles.
Conceivably, examining variations in crust thickness might provide new insights into past glacial cycles and help scientists to better narrow down sea-level change in the deep past, says Wunsch. Meanwhile, a high-resolution topography survey carried out last summer across the Juan de Fuca ridge off the coast of Oregon and Washington offers an opportunity to test the team’s hypothesis further. “We’re going to look at that data very soon,” says Katz.
Reference:
Nature doi:10.1038/nature.2015.16856
Note : The above story is based on materials provided by Nature. The original article was written by Quirin Schiermeier.
A 15-million year old fossil gastropod, Ecphora, from the Calvert Cliffs of southern Maryland is depicted. The golden brown color arises from the original shell-binding proteins and pigments preserved in the mineralized shell. Credit: John Nance
A team of Carnegie scientists have found “beautifully preserved” 15 million-year-old thin protein sheets in fossil shells from southern Maryland. Their findings are published in the inaugural issue of Geochemical Perspectives Letters.
The team–John Nance, John Armstrong, George Cody, Marilyn Fogel, and Robert Hazen–collected samples from Calvert Cliffs, along the shoreline of the Chesapeake Bay, a popular fossil collecting area. They found fossilized shells of a snail-like mollusk called Ecphora that lived in the mid-Miocene era–between 8 and 18 million years ago.
Ecphora is known for an unusual reddish-brown shell color, making it one of the most distinctive North American mollusks of its era. This coloration is preserved in fossilized remains, unlike the fossilized shells of many other fossilized mollusks from the Calvert Cliffs region, which have turned chalky white over the millions of years since they housed living creatures.
Shells are made from crystalline compounds of calcium carbonate interleaved with an organic matrix of proteins and sugars proteins and sugars. These proteins are called shell-binding proteins by scientists, because they help hold the components of the shell together.They also contain pigments, such as those responsible for the reddish-brown appearance of the Ecphora shell. These pigments can bind to proteins to form a pigment-protein complex.
The fact that the coloration of fossilized Ecphora shells is so well preserved suggested to the research team that shell proteins bound to these pigments in a complex might also be preserved. They were amazed to find that the shells, once dissolved in dilute acid, released intact thin sheets of shell proteins more than a centimeter across. Chemical analysis including spectroscopy and electron microscopy of these sheets revealed that they are indeed shell proteins that were preserved for up to 15 million years.
“These are some of the oldest and best-preserved examples of a protein ever observed in a fossil shell,” Hazen said.
Remarkably, the proteins share characteristics with modern mollusk shell proteins. They both produce thin, flexible sheets of residue that’s the same color as the original shell after being dissolved in acid. Of the 11 amino acids found in the resulting residue, aspartate and glutamate are prominent, which is typical of modern shell proteins. Further study of these proteins could be used for genetic analysis to trace the evolution of mollusks through the ages, as well as potentially to learn about the ecology of the Chesapeake Bay during the era in which Ecphora thrived.
Recent earthquakes (yellow) and volcanoes (red) of the world plotted against tectonic plate boundaries.
CProfessors Tim Stern and Martha Savage and Drs Simon Lamb and Rupert Sutherland from Victoria’s School of Geography, Environment and Earth Sciences—along with scientists from GNS Science and universities in the United States and Japan—developed new methods to get the most detailed images yet of the base of the tectonic plate beneath Wellington.
A paper on the team’s finding, entitled A seismic reflection image for the base of a tectonic plate, has been published in the February 5, 2015 edition of the prestigious international scientific journal, Nature.
The team recorded reflected seismic waves from an array of controlled underground dynamite explosions across the southern part of the North Island, which gave the scientists an image of the bottom of the Pacific Plate, 100 kilometres beneath the Earth’s surface. The recordings were many times higher resolution than what has been previously achieved, and showed that Earth’s tectonic plates are gliding on a distinct layer of ‘soft’ rock, only 10 kilometres thick and weak enough to allow the plates to shift many centimetres per year.
“The idea that Earth’s surface consists of a mosaic of moving plates is a well-established scientific paradigm, but it had never been clear about what actually moves the plates around,” says Professor Stern. “To work this out requires an understanding of what happens at the bottom of a tectonic plate. It’s been difficult to obtain the necessary detailed images at such great depths using the usual method of recording natural earthquake waves.
Cartoon showing the oceanic lithosphere of the Pacific plate subducting beneath the continental Australian plate. The blown up piece shows what we interpret to the be a ~ 10 km thick channel at the base of the plate where melts have ponded, and high strain rates have focused and localised the melt into a thin layer. This channel is likely to be of low viscosity and weak, and effectively allows the plates to slide unhindered by any convective connection to the viscous mantle beneath. Credit: Tim Stern
“But by generating our own seismic waves using higher frequency dynamite shots we were able to see how they became modified as they passed through different layers in the earth. This, along with some new techniques in seismic reflection processing, allowed us to obtain the most detailed image yet of an oceanic tectonic plate.”
Professor Stern says the thinner layer beneath the plate appears to contain pockets of molten rock that make it easier for the plates to slide on. “This means that the plates can be pushed and pulled around without strong resistance at the base. A weak slippery base also explains why tectonic plates can sometimes abruptly change the direction in which they’re slipping. It’s a bit like a ski sliding on snow.
“Understanding this boundary between the base of cold, rigid tectonic plates and the underlying hot, convecting mantle underneath is central to our knowledge of plate tectonics and the very formation and evolution of our planet.”
Professor Stern says being recognised by such an internationally-respected scientific journal indicates the significance of the team’s discovery. “This study also demonstrates the long-standing ability of New Zealand’s geoscience community to leverage international funds—in this case from Japan and the United States—into New Zealand for the purposes of making fundamental discoveries about how the earth works.”
Reference:
“A seismic reflection image for the base of a tectonic plate.” Nature 518, 85–88 (05 February 2015) DOI: 10.1038/nature14146
Pre-Tohoku earthquake (from December 2003 until the occurrence of the mega-thrust event) b-values resolved along the subduction interface: high b-values in the low-stress normal-faulting outer-rise area; low and very low b-values along the highly-stressed megathrust, high b-values in the magma source region at depth (reflecting dehydration and partial melting below the volcanic front). Star: 2011 M9 epicenter, white contours: Tohoku-oki earthquake slip model (Yagi and Fukahata, 2011) indicating the M9 highest slip area (previously locked, highly stressed asperity, reflected by very low b-values); triangles: volcanoes. Inset: Cross-sectional view at 40°N, as indicated, showing the relation between b-values and the tectonic processes at the subduction zone. Credit: Image courtesy of University of Tsukuba
Associate Professor Bogdan Enescu, Faculty of Life and Environmental Sciences, University of Tsukuba, collaborated with colleagues at the Swiss Federal Institute of Technology in Zurich (ETH Zurich), to show that the stress recovery following the 2011 M9.0 Tohoku-oki earthquake has been significantly faster than previously anticipated; specifically, the stress-state at the plate interface returned within just a few years to levels observed before the megathrust event. In addition, since there is no observable spatial difference in the stress state along the megathrust zone, it is difficult to predict the location and extent of future large ruptures.
Constraining the recurrence of megathrust earthquakes is genuinely important for hazard assessment and mitigation. The prevailing approach to model such events worldwide relies on the segmentation of the subduction zone and quasi-periodic recurrence due to constant tectonic loading. The researchers analyzed earthquakes recorded along a 1,000-km-long section of the subducting Pacific Plate beneath Japan since 1998 to map the relative frequency of small to large earthquakes (the so-called “b-value” parameter — which on average is close to 1.0), in both space and time. Evidence from laboratory experiments, numerical modeling and natural seismicity indicates that the b-value is negatively correlated with the differential stress. The present analysis reveals that the spatial distribution of b-values reflects well the tectonic processes accompanying plate motion. However, there is no evidence of distinct earthquake-generation regions along the megathrust, associated with the so-called “characteristic earthquakes.”
Nevertheless, the authors show that parts of the plate interface that ruptured during the 2011 Tohoku-oki earthquake were highly stressed in the years leading up to the earthquake, as expressed by mapped, very low regional b-values. Although the stress was largely released during the 2011 rupture, thus leading to an increase in b-values immediately after the megathrust event, the stress levels (i.e., b-values) quickly recovered to pre-megaquake levels within just a few years. This suggests that the megathrust zone is likely ready for large earthquakes any time with a low but on average constant probability.
The study concludes that large earthquakes may not have a characteristic location, size or recurrence interval, and might therefore occur more randomly distributed in time. The authors bring also strong evidence that the size distribution of earthquakes is sensitive to stress variations and its careful monitoring can improve the seismic hazard assessment of the megathrust zone.
Reference:
Thessa Tormann, Bogdan Enescu, Jochen Woessner, Stefan Wiemer. Randomness of megathrust earthquakes implied by rapid stress recovery after the Japan earthquake. Nature Geoscience, 2015; 8 (2): 152 DOI: 10.1038/ngeo2343
Magma from undersea eruptions congealed into forms known as pillow basalts on the Juan De Fuca Ridge, off the U.S. Pacific Northwest. A new study shows such eruptions wax and wane on regular schedules. Credit: Deborah Kelley/University of Washington
Vast ranges of volcanoes hidden under the oceans are presumed by scientists to be the gentle giants of the planet, oozing lava at slow, steady rates along mid-ocean ridges. But a new study shows that they flare up on strikingly regular cycles, ranging from two weeks to 100,000 years — and, that they erupt almost exclusively during the first six months of each year. The pulses — apparently tied to short- and long-term changes in earth’s orbit, and to sea levels–may help trigger natural climate swings.
Scientists have already speculated that volcanic cycles on land emitting large amounts of carbon dioxide might influence climate; but up to now there was no evidence from submarine volcanoes. The findings suggest that models of earth’s natural climate dynamics, and by extension human-influenced climate change, may have to be adjusted. The study appears this week in the journal Geophysical Research Letters.
“People have ignored seafloor volcanoes on the idea that their influence is small — but that’s because they are assumed to be in a steady state, which they’re not,” said the study’s author, marine geophysicist Maya Tolstoy of Columbia University’s Lamont-Doherty Earth Observatory. “They respond to both very large forces, and to very small ones, and that tells us that we need to look at them much more closely.” A related study by a separate team this week in the journal Science bolsters Tolstoy’s case by showing similar long-term patterns of submarine volcanism in an Antarctic region Tolstoy did not study.
Volcanically active mid-ocean ridges crisscross earth’s seafloors like stitching on a baseball, stretching some 37,000 miles. They are the growing edges of giant tectonic plates; as lavas push out, they form new areas of seafloor, which comprise some 80 percent of the planet’s crust. Conventional wisdom holds that they erupt at a fairly constant rate–but Tolstoy finds that the ridges are actually now in a languid phase. Even at that, they produce maybe eight times more lava annually than land volcanoes. Due to the chemistry of their magmas, the carbon dioxide they are thought to emit is currently about the same as, or perhaps a little less than, from land volcanoes — about 88 million metric tons a year. But were the undersea chains to stir even a little bit more, their CO2 output would shoot up, says Tolstoy.
Alternating ridges and valleys formed by volcanism near the East Pacific Rise, a mid-ocean ridge in the Pacific Ocean. Such formations indicate ancient highs and lows of volcanic activity. (Haymon et al., NOAA-OE, WHOI)
Some scientists think volcanoes may act in concert with Milankovitch cycles–repeating changes in the shape of earth’s solar orbit, and the tilt and direction of its axis — to produce suddenly seesawing hot and cold periods. The major one is a 100,000-year cycle in which the planet’s orbit around the sun changes from more or less an annual circle into an ellipse that annually brings it closer or farther from the sun. Recent ice ages seem to build up through most of the cycle; but then things suddenly warm back up near the orbit’s peak eccentricity. The causes are not clear.
Enter volcanoes. Researchers have suggested that as icecaps build on land, pressure on underlying volcanoes also builds, and eruptions are suppressed. But when warming somehow starts and the ice begins melting, pressure lets up, and eruptions surge. They belch CO2 that produces more warming, which melts more ice, which creates a self-feeding effect that tips the planet suddenly into a warm period. A 2009 paper from Harvard University says that land volcanoes worldwide indeed surged six to eight times over background levels during the most recent deglaciation, 12,000 to 7,000 years ago. The corollary would be that undersea volcanoes do the opposite: as earth cools, sea levels may drop 100 meters, because so much water gets locked into ice. This relieves pressure on submarine volcanoes, and they erupt more. At some point, could the increased CO2 from undersea eruptions start the warming that melts the ice covering volcanoes on land?
That has been a mystery, partly because undersea eruptions are almost impossible to observe. However, Tolstoy and other researchers recently have been able to closely monitor 10 submarine eruption sites using sensitive new seismic instruments. They have also produced new high-resolution maps showing outlines of past lava flows. Tolstoy analyzed some 25 years of seismic data from ridges in the Pacific, Atlantic and Arctic oceans, plus maps showing past activity in the south Pacific.
The long-term eruption data, spread over more than 700,000 years, showed that during the coldest times, when sea levels are low, undersea volcanism surges, producing visible bands of hills. When things warm up and sea levels rise to levels similar to the present, lava erupts more slowly, creating bands of lower topography. Tolstoy attributes this not only to the varying sea level, but to closely related changes in earth’s orbit. When the orbit is more elliptical, Earth gets squeezed and unsqueezed by the sun’s gravitational pull at a rapidly varying rate as it spins daily — a process that she thinks tends to massage undersea magma upward, and help open the tectonic cracks that let it out. When the orbit is fairly (though not completely) circular, as it is now, the squeezing/unsqueezing effect is minimized, and there are fewer eruptions.
The idea that remote gravitational forces influence volcanism is mirrored by the short-term data, says Tolstoy. She says the seismic data suggest that today, undersea volcanoes pulse to life mainly during periods that come every two weeks. That is the schedule upon which combined gravity from the moon and sun cause ocean tides to reach their lowest points, thus subtly relieving pressure on volcanoes below. Seismic signals interpreted as eruptions followed fortnightly low tides at eight out of nine study sites. Furthermore, Tolstoy found that all known modern eruptions occur from January through June. January is the month when Earth is closest to the sun, July when it is farthest — a period similar to the squeezing/unsqueezing effect Tolstoy sees in longer-term cycles. “If you look at the present-day eruptions, volcanoes respond even to much smaller forces than the ones that might drive climate,” she said.
Daniel Fornari, a senior scientist at Woods Hole Oceanographic Institution not involved in the research, called the study “a very important contribution.” He said it was unclear whether the contemporary seismic measurements signal actual lava flows or just seafloor rumbles and cracking. But, he said, the study “clearly could have important implications for better quantifying and characterizing our assessment of climate variations over decadal to tens to hundreds of thousands of years cycles.”
Edward Baker, a senior ocean scientist at the National Oceanic and Atmospheric Administration, said, “The most interesting takeaway from this paper is that it provides further evidence that the solid Earth, and the air and water all operate as a single system.”
The research for this paper was funded in large part by the U.S. National Science Foundation.
Tracking glaciers with accelerators. Credit: Photo by Rodrigo A. SEPÚLVEDA SCHULZ
Geologists once thought that, until about 18,000 years ago, a mammoth glacier covered the top two-thirds of Ireland. Recently, however, they found evidence that it wasn’t just the top two-thirds: The Irish glacier was much larger, completely engulfing the country and extending far offshore.
They learned this with the help of a particle accelerator.
Glaciers are always on the move, advancing or retreating as fast as 30 meters a day or as slow as half a meter a year. During the most recent ice age, huge glaciers spread over much of Earth’s northern climes, extending all the way from the northern tip of Greenland to Cape Cod and across to Chicago, which was buried under a kilometer of ice. It was the same in Europe, with parts of the British Isles, Germany, Poland and Russia all hidden beneath an enormous ice sheet.
“For the last 2.5 million years of Earth’s history, we’ve had this pattern of alternating ice ages and interglacials,” says Fred Phillips, a professor in New Mexico Tech’s Department of Earth and Environmental Science who, among other things, is an expert at dating the movements of glaciers.
“Trying to understand these cycles — to understand geographical distribution of climate fluctuations and trying to pin down the chronology — has preoccupied scientists for 200 years now.”
Over the past 30 years, scientists have begun to use particle accelerators to help them track how these glaciers move.
The process begins with a globetrotting geologist and some huge rocks. As a glacier recedes, it will sometimes pluck a boulder from its depths and push it into daylight. While trapped beneath the ice, the boulder is shielded from the barrage of cosmic rays that continuously assaults Earth’s surface. But as soon as the boulder is exposed, cosmic rays begin to interact with the atoms inside the rock, rapidly producing rare isotopes called cosmogenic nuclides, such as helium-3, neon-21 or beryllium-10.
To determine just how long ago the boulder was forced to the surface, geologists like Phillips use a hammer and chisel — or, sometimes, rock saws and small explosive devices — to remove a chunk of rock about the size of a grapefruit. They bring that sample back to the lab, grind it up and extract one specific mineral, such as quartz, that produces cosmogenic nuclides at a known rate.
1. Geologists in Antarctica use a hammer and chisel to sample the upper few centimeters of a boulder for cosmogenic nuclide dating.
2. Bethan Davies samples a boulder for cosmogenic nuclide dating in Greenland. Courtesy of: David Roberts and Bethan Davies, www. AntarcticGlaciers .org
After isolating one particular nuclide from that mineral, they send a beam of cesium ions at the sample. That adds an extra electron to atoms within the sample, forming negative elemental or molecular ions. These ions are sent into an accelerator beam and smashed through a thin foil or gas, which strips them of electrons and destroys any remaining molecules. Finally, the ions are sent into a detector that counts the ratio of unstable to stable atoms, revealing the amount of cosmogenic nuclides. The more cosmogenic nuclides in the sample, the more time has elapsed since the glacier ejected the boulder.
The original idea for this type of geological dating came from none other than Raymond Davis Jr., the Brookhaven National Laboratory nuclear chemist who won a Nobel Prize for detecting neutrinos streaming from the sun. Davis came up with the idea working in collaboration with Oliver Schaeffer, an expert in the environmental production of background radioactivity.
Although the duo correctly set forth the basic experimental concept for using cosmogenic nuclides to date rock samples in the mid-1950s, it took nearly 30 years for detector technologies to catch up with their ideas. Once possible, the technique took off. “Since the mid-1980s, there have been thousands of scientific papers published on glacial chronologies and other geological dating using this method,” Phillips says.
Today, Phillips says, significant effort is being made to understand the rise and fall of the West Antarctic Ice Sheet.
“This is important because it looks like now this ice sheet is in a state of slow collapse, which could raise sea level by about 5 meters,” he says. “Understanding what controls the extent of that ice is critically important.”
By understanding the past, researchers like Phillips might better understand what’s to come.
Illustration of the ocean floor offshore West-Svalbard, including the Vestnesa Ridge. Credit: Andreia Plaza Faverola/CAGE
Natural seepage of methane offshore the Arctic archipelago Svalbard has been occurring periodically for at least 2,7 million years. Major events of methane emissions happened at least twice during this period, according to a new study.
We worry about greenhouse gas methane. It´s lifetime in the atmosphere is much shorter than CO2´s, but the impact of methane on climate change is over 20 times greater than CO2 over a 100-year period.
60 percent of the methane in the atmosphere comes from emissions from human activities. But methane is a natural gas, gigatonnes of it trapped under the ocean floor in the Arctic.
And it is leaking. And has been leaking for the longer time than the humans have roamed the Earth.
” Our planet is leaking methane gas all the time. If you go snorkeling in the Caribbean you can see bubbles raising from the ocean floor at 25 meters depth. We studied this type of release, only in a much deeper, colder and darker environment. And found out that it has been going on, periodically, for as far back as 2,7 million years.” says Andreia Plaza Faverola the primary author behind a new paper in Geophysical Research Letters.
She is talking about Vestnesa Ridge in Fram Strait, a thousand meters under the surface of the Arctic Ocean, offshore West-Svalbard. Here, enormous, 800 meters high gas flares rise from the seabed. That’s the size of the tallest manmade structure in the world — Burj Khalifa in Dubai.
“Half of Vestnesa Ridge is showing very active seepage of methane. The other half is not. But there are obvious pockmarks on the inactive half, cavities and dents in the ocean floor, that we recognized as old seepage features. So we were wondering what activates, or deactivates, the seepage in this area.,” says Plaza Faverola.
She, and a team of marine geophysicists from CAGE, used the P-Cable technology, to figure it out. It is a seismic instrument that is towed behind a research vessel. It recorded the sediments beneath these pockmarks. P-Cable renders images that look like layers of a cake and enables scientists to visualize deep sediments in 3D.
” We know from other studies in the region that the sediments we are looking at in our seismic data are at least 2.7 million years old. This is the period of increase of glaciations in the Northern Hemisphere, which influenced the sediment. The P-Cable helped us to see features in this sediment, associated with gas release in the past. ”
“These features can be buried pinnacles, or cavities, that form what we call gas chimneys in the seismic data. Gas chimneys appear like vertical disturbances in the layers of our sedimentary cake. This enabled us to reconstruct the evolution of gas expulsion from this area, for at least 2,7 million years.” says Andreia Plaza Faverola.
The seismic signal penetrated into 400 to 500 meters of sediment to map this timescale.
How is the methane released?
By using this method, scientists were able to identify two major events of gas emission throughout this time period: One 1,8 million years ago, the other 200,000 years ago.
This means that there is something that activated and deactivated the emissions several times. Plaza Faverola´s paper gives a plausible explanation: It is the movement of the tectonic plates that influences the gas release. Vestnesa is not like California though, riddled with earthquakes because of the moving plates. The ridge is on a so-called passive margin. But as it turns out, it doesn´t take a huge tectonic shift to release the methane stored under the ocean floor.
“Even though Vestnesa Ridge is on a passive margin, it is between two oceanic ridges that are slowly spreading. These spreading ridges resulted in separation of Svalbard from Greenland and opening of the Fram Strait. The spreading influences the passive margin of West-Svalbard, and even small mechanical collapse in the sediment can trigger seepage.” says Faverola.
Where does the methane come from? The methane is stored as gas hydrates, chunks of frozen gas and water, up to hundreds of meters under the seabed. Vestnesa hosts a large gas hydrate system. There is some concern that global warming of the oceans may melt this icy gas and release it into the atmosphere. That is not very likely in this area, according to Andreia Plaza Faverola.
” This is a deep water gas hydrate system, which means that it is in permanently cold waters and under a lot of pressure. This pressure keeps the hydrates stable and the whole system is not vulnerable to global temperature changes. But under the stable hydrates there is gas that is not frozen. The amount of this gas may increase if hydrates melt at the base of this stability zone, or if gas from deeper in the sediments arrives into the system. This could increase the pressure in this part of the system, and the free gas may escape the seafloor through chimneys. Hydrates would still remain stable in this scenario[IS8] .”
Historical methane peaks coincide with increase in temperature
Throughout Earth´s history there have been several short periods of significant increase in temperature. And these periods often coincide with peaks of methane in the atmosphere, as recorded in ice cores. Scientists such as Plaza Faverola are still debating about the cause of this methane release in the past.
” One hypotheses is that massive gas release from geological sources, such as volcanos or ocean sediments may have influenced global climate. What we know is that there is a lot of methane released at present time from the ocean floor. What we need to find out is if it reaches the atmosphere, or if it ever did.”
Historical events of methane release, such as the ones in the Vestnesa Ridge, provide crucial information that can be used in future climate modeling. Knowing if these events repeat, and identifying what makes them happen, may help us to better predict the potential influence of methane from the oceans on future climate.
Video:
Reference:
A. Plaza-Faverola, S. Bünz, J. E. Johnson, S. Chand, J. Knies, J. Mienert, P. Franek. Role of tectonic stress in seepage evolution along the gas hydrate-charged Vestnesa Ridge, Fram Strait. Geophysical Research Letters, 2015; DOI: 10.1002/2014GL062474
A composite image of the Western hemisphere of the Earth. Credit: NASA
New evidence showing the level of atmospheric CO2 millions of years ago supports recent climate change predications from the Intergovernmental Panel on Climate Change (IPCC).
A multinational research team, led by scientists at the University of Southampton, has analysed new records showing the CO2 content of the Earth’s atmosphere between 2.3 to 3.3 million years ago, over the Pliocene.
During the Pliocene, the Earth was around 2ºC warmer than it is today and atmospheric CO2 levels were around 350-400 parts per million (ppm), similar to the levels reached in recent years.
By studying the relationship between CO2 levels and climate change during a warmer period in Earth’s history, the scientists have been able to estimate how the climate will respond to increasing levels of carbon dioxide, a parameter known as ‘climate sensitivity’.
The findings, which have been published in Nature, also show how climate sensitivity can vary over the long term.
“Today the Earth is still adjusting to the recent rapid rise of CO2 caused by human activities, whereas the longer-term Pliocene records document the full response of CO2-related warming,” says Southampton’s Dr Gavin Foster, co-author of the study.
“Our estimates of climate sensitivity lie well within the range of 1.5 to 4.5ºC increase per CO2 doubling summarised in the latest IPCC report. This suggests that the research community has a sound understanding of what the climate will be like as we move toward a Pliocene-like warmer future caused by human greenhouse gas emissions.”
Lead author of the study, Dr Miguel Martínez-Botí, also from Southampton said: “Our new records also reveal an important change at around 2.8 million years ago, when levels rapidly dropped to values of about 280 ppm, similar to those seen before the industrial revolution. This caused a dramatic global cooling that initiated the ice-age cycles that have dominated Earth’s climate ever since.”
The research team also assessed whether climate sensitivity was different in warmer times, like the Pliocene, than in colder times, like the glacial cycles of the last 800,000 years.
Professor Eelco Rohling of The Australian National University in Canberra says: “We find that climate change in response to CO2 change in the warmer period was around half that of the colder period. We determine that this difference is driven by the growth and retreat of large continental ice sheets that are present in the cold ice-age climates; these ice sheets reflect a lot of sunlight and their growth consequently amplifies the impact of CO2 changes.”
Professor Richard Pancost from the University of Bristol Cabot Institute, added: “When we account for the influence of the ice sheets, we confirm that the Earth’s climate changed with a similar sensitivity to overall forcing during both warmer and colder climates.”
Reference:
M. A. Martínez-Botí, G. L. Foster, T. B. Chalk, E. J. Rohling, P. F. Sexton, D. J. Lunt, R. D. Pancost, M. P. S. Badger, D. N. Schmidt. Plio-Pleistocene climate sensitivity evaluated using high-resolution CO2 records. Nature, 2015; 518 (7537): 49 DOI: 10.1038/nature14145
Scientists pumped half a tonne of explosive material into 50km-deep holes spread nearly 100km across New Zealand’s North Island to measure rock layers beneath the surface Photograph: Diana Plater/AAP
Geologists may have finally explained how tectonic plates shift by blowing up hundreds of kilograms of dynamite in New Zealand.
Half a tonne of explosive slurry was pumped into a dozen, steel-cased holes spread nearly 100km across New Zealand’s north island.
The seismic waves produced by the subsequent explosion reached the base of the tectonic plate and rebounded to the surface, where they were recorded by more than 1,000 seismographs.
Because seismic waves encode information about each of the layers they pass through, an international team of researchers was able to use them to produce detailed images of what lies beneath the earth’s surface.
They revealed the existence of a narrow, lubricating layer of rock about 73km deep, over which the plate “skied” several centimetres a year.
The results are published in the latest issue of the scientific journal Nature.
One of the researchers, professor Tim Stern of Victoria University, Wellington, said earlier studies had relied on recording the seismic waves produced by earthquakes.
“But those earthquake waves are very low-frequency, wobbly looking waves, and they haven’t really given us the details we need,” he said.
Detonating 500kg of dynamite – the equivalent of more 2,600 sticks – provided far sharper echoes.
The 50m-deep explosive holes were dug in a line parallel to the border of the Pacific and Australian plates, Stern said. The two plates meet at a relatively shallow 12- to 15-degree angle, making the area ideal for rebounding seismic waves, which he likened to “bouncing light off a mirror”.
Once triggered, the explosion caused the earth to shake and produced a “big whoomp” that could be heard from 10km away. “But that’s about all,” Stern said.
While the discovery of the slippery 10km layer explains how the plates move, what causes them to do so remains unclear.
One leading theory suggests the plates are pulled or pushed along their edges. Another, posits that the plates are connected to a deeper layer of hot, convecting mantle and getting dragged.
Stern said the research showed “there’s still fundamental discoveries to be made” in the theory of plate tectonics, which has dominated earth science since the 1960s.
A forerunner of the idea was suggested in 1912 by a German meteorologist, Alfred Wegener, who observed that the east coast of South America and the west coast of Africa fit together like a puzzle.
He suggested the world’s continents had once been fused together in a supercontinent he named Pangaea (“all the world”), but had since broken up and drifted to their present locations.
Earlier theories had suggested the world’s continents had been connected by massive land bridges, which have since broken off and sunk.
Artist’s conception of an asteroid crashing into the Yucatan Peninsula about 65 million years ago. Credit: Donald E. Davis/NASA
What suddenly made the dinosaurs disappear 65 million or 66 million years ago? Whatever it was, all indications show that it was a massive extinction event. The fossil record not only shows dinosaurs disappearing, but also numerous other species of the era. Whatever it was, there was a sudden change in the environment that changed evolution forever.
The leading theory for this change is a small body (likely an asteroid or a comet) that slammed into Mexico’s Yucatan Peninsula. The impact’s force generated enough debris to block the Sun worldwide, killing any survivors of starvation.
There have been numerous theories proposed for the dinosaurs’ death, but in 1980 more evidence arose for a huge impact on the Earth. This happened when a father-son University of California, Berkeley research team—Luis Alvarez and Walter Alvarez—discovered a link with a 110-mile (177-kilometer) wide impact crater near the Yucatan coast of Mexico. It’s now known as Chicxulub.
Chicxulub crater in Mexico. Credit: Wikipedia/NASA
It sounds surprising that such a huge crater wasn’t found until that late, especially given satellites had been doing Earth observation for the better part of 20 years at that point. But as NASA explains, “Chicxulub … eluded detection for decades because it was hidden (and at the same time preserved) beneath a kilometer of younger rocks and sediments.”
The data came from a Mexican company that was seeking oil in the region. The geologists saw the structure and guessed, from its circular shape, that it was an impact crater. Further observations were done using magnetic and gravity data, NASA said, as well as space observations (including at least one shuttle mission).
The layer
The asteroid’s impact on Earth was quite catastrophic. Estimated at six miles (9.7 kilometers) wide, it carved out a substantial amount of debris that spread quickly around the Earth, aided by winds in the atmosphere.
If you look in the fossil record all over the world, you will see a layer that is known as the “K-T Boundary”, referring to the boundary between the Cretaceous and Tertiary periods in geologic history. This layer, says the University of California, Berkeley, is made up of “glassy spheres or tektites, shocked quartz and a layer of iridium-enriched dust.”
K-T Boundary. Credit: NASA Earth Observatory
Of note, iridium is a rare element on the surface of the Earth, but it’s fairly common in meteorites. (Some argue that the iridium could have come from volcanic eruptions churning it up from inside the Earth; for more information, see this Universe Today story.)
Was it simply ‘the last straw’?
While an asteroid (or comet) striking the Earth could certainly cause all the catastrophic events listed above, some scientists believe the dinosaurs were already on their last legs (so to speak) before the impact took place. Berkeley points to “dramatic climate variation” in the million years preceding the event, such as very cold periods in the tropical environment that the dinosaurs were used to.
What might have caused this were several volcanic eruptions in India around the same time. Some scientists believe it was the volcanic eruptions themselves that caused the extinction and that the impact was not principally to blame, since the eruptions could also have produced the iridium layer. But Berkeley’s Paul Renne said the eruptions were more a catalyst for weakening the dinosaurs.
“These precursory phenomena made the global ecosystem much more sensitive to even relatively small triggers, so that what otherwise might have been a fairly minor effect shifted the ecosystem into a new state,” Renne stated in 2013. “The impact was the coup de grace.”
Note : The above story is based on materials provided by Universe Today. The original article was written by Elizabeth Howell.
The richest gold ore in Witwatersrand is found in thin layers rich in carbon, plating fibres of ancient microbial life forms. (Photo: James St. John / Wikimedia Commons)
The Witwatersrand Basin in South Africa holds the world’s largest gold deposits across a 200-km long swathe. Individual ore deposits are spread out in thin layers over areas up to 10 by 10 km and contain more gold than any other gold deposit in the world. Some 40% of the precious metal that has been found up to the present day comes from this area, and hundreds of tons of gold deposits still lie beneath the earth. The manner in which these giant deposits formed is still debated among geologists. Christoph Heinrich, Professor of Mineral Resources at ETH and the University of Zurich, recently published a new explanation in the journal Nature Geoscience, trying to reconcile the contradictions of two previously published theories.
The prevailing ‘placer gold’ theory states that the gold at Witwatersrand was transported and concentrated through mechanical means as metallic particles in river sediment. Such a process has led to the gold-rich river gravels that gave rise to the Californian gold rush. Here, nuggets of placer gold have accumulated locally in river gravels in the foothills of the Sierra Nevada, where primary gold-quarz veins provide a nearby source of the nuggets.
But no sufficiently large source exists in the immediate sub-surface of the Witwatersrand Basin. This is one of the main arguments of proponents of the ‘hydrothermal hypothesis’, according to which gold, chemically dissolved in hot fluid, passed into the sediment layers half a billion years after their deposition. For this theory to work, a 10 km thick blanket of later sediments would be required in order to create the required pressure and temperature. However, the hydrothermal theory is contradicted by geological evidence that the gold concentration must have taken place during the formation of host sediments on the Earth’s surface.
Heinrich believes the concentration of gold took place at the Earth’s surface, indeed by flowing river water, but in chemically dissolved form. With such a process, the gold could be easily ‘collected’ from a much larger catchment area of weathered, slightly gold-bearing rocks. The resource geologist examined the possibility of this middle way, by calculating the chemical solubility of the precious metal in surface water under the prevailing atmospheric and climatic conditions.
Experimental data shows that the chemical transport of gold was indeed possible in the early stages of Earth evolution. The prerequisite was that the rainwater had to be at least occasionally very rich in hydrogen sulphide. Hydrogen sulphide binds itself in the weathered soil with widely distributed traces of gold to form aqueous gold sulphide complexes, which significantly increases the solubility of the gold. However, hydrogen sulphide in the atmosphere and sulphurous gold complexes in river water are stable only in the absence of free oxygen. “Quite inhospitable environmental conditions must have dominated, which was possible only three billion years ago during the Archean eon,” says Heinrich. “It required an oxygen-free atmosphere that was temporarily very rich in hydrogen sulphide — the smell of rotten eggs.” In today’s atmosphere, oxygen oxidises all hydrogen sulphide, thus destroying gold’s sulphur complex in a short time, which is why gold is practically insoluble in today’s river water.
Volcanoes and bacteria as important factors
In order to increase the sulphur concentration of rainwater sufficiently in the Archean eon, basaltic volcanism of gigantic proportions was required at the same time. Indeed, in other regions of South Africa there is evidence of giant basaltic eruptions overlapping with the period of the gold concentration.
A third factor required for the formation of gold deposits at Witwatersrand is a suitable location for concentrated precipitation of the gold. The richest deposits of gold ore in the basin are found in carbon-rich layers, often just millimetres to centimeters thick, but which stretch for many kilometres. These thin layers contain such high gold concentrations that mining tunnels scarcely a metre high some three kilometres below the Earth’s surface are still worthwhile.
Hard and dangerous labour: The mines provide no place to stand. (Photo: Courtesy Prof. C. Heinrich)
The carbon probably stems from the growth of bacteria on the bottom of shallow lakes and it’s here that the dissolved gold precipitated chemically, according to Heinrich’s interpretation.
The nature of these life forms is not well known. “It’s possible that these primitive organisms actively adsorbed the gold,” Heinrich speculates. “But a simple chemical reduction of sulphur-complexed gold in water to elementary metal on an organic material is sufficient for a chemical ‘gilding’ of the bottom of the shallow lakes.”
The gold deposits in the Witwatersrand, which are unique worldwide, could have thus been formed only during a certain period of the Earth’s history: after the development of the first continental life forms in shallow lakes at least 3 billion years ago, but before the first emergence of free oxygen in the Earth’s atmosphere approximately 2.5 billion years ago.
Reference:
Christoph A. Heinrich. Witwatersrand gold deposits formed by volcanic rain, anoxic rivers and Archaean life. Nature Geoscience, 2015; DOI: 10.1038/ngeo2344
Note : The above story is based on materials provided by ETH Zürich. The original article was written by Peter Rüegg.
North America traveled in fast company back in its youth.
A new study led by Michigan Technological University geophysicist Aleksey Smirnov reveals that 1.1 billion years ago, the North American tectonic plate scooted along at a blistering 24.6 centimeters—about 10 inches—per year.
While it may not seem to be shattering any speed records, that’s twice as fast as continental plates typically traveled in their wanderings over the earth’s surface back in Precambrian times. Oceanic plates moved that quickly, but they are also much thinner, only 10 to 15 kilometers deep. Continental plates are up to 70 kilometers (43 miles) thick.
These days, tectonic plates—15-20 huge, interlocking pieces that make up the earth’s crust—are even slower. Nevertheless, their movements are partially responsible for geological phenomena like earthquakes, volcanoes and mountain building.
Smirnov’s team made its discovery while investigating a totally different problem. Every time the earth’s magnetic field switches 180 degrees—which happens every few hundred thousand years or so—the change is recorded in certain volcanic minerals that are formed as lava cools. The only apparent exception to the 180-degree rule was found during earlier investigations of the “fossil magnetism” of the rocks in Michigan’s Keweenaw Peninsula. Scientists were surprised to find what looked like a switch of about 200 degrees. In other words, the magnetic north and south poles seemed to be seriously off kilter at one point about a billion years ago.
Smirnov’s group looked at rocks from the same era at the Coldwell Complex, located in Ontario near the town of Marathon. There, a more-complete fossil magnetization record is available. They found that it wasn’t the earth’s magnetic field that had moved so dramatically: it was the North American Plate itself. Their discovery validates an earlier hypothesis that the continent was breaking speed records back in the day.
But what engine could drive a continental plate at such a clip? Smirnov believes the answer may lie deep beneath the surface of the earth.
Mantle Activity
“We know there was a lot of mantle activity at the time,”he said. The mantle is the layer between the earth’s crust and its core. “The continental and oceanic plates float atop this thick layer of semi-molten rock, and at this point in the Precambrian Era all the land masses were drifting together to form the supercontinent Rodinia.
“We had a very vigorous mantle at that time, and that would move this huge continental plate,” said Smirnov.
Reference:
“Paleomagnetism of the ~1.1 Ga Coldwell Complex (Ontario, Canada): Implications for Proterozoic Geomagnetic Field Morphology and Plate Velocities,”coauthored by Smirnov, PhD student Evgeniy Kulakov and Professor Jimmy Diehl, all of Michigan Tech, is published Dec. 21 in the Journal of Geophysical Research: Solid Earth. DOI: 10.1002/2014JB011463
This is an artist rendering of what South America’s oldest known monkey might have looked like. It was about the size of a squirrel, but with a longer tail, and probably weighed less than 250 grams (~0.5 lbs). Credit: Artist: Jorge González
For millions of years, South America was an island continent. Geographically isolated from Africa as a result of plate tectonics more than 65 million years ago, this continent witnessed the evolution of many unfamiliar groups of animals and plants. From time to time, animals more familiar to us today — monkeys and rodents among others — managed to arrive to this island landmass, their remains appearing abruptly in the fossil record. Yet, the earliest phases of the evolutionary history of monkeys in South America have remained cloaked in mystery. Long thought to have managed a long transatlantic journey from Africa, evidence for this hypothesis was difficult to support without fossil data
A new discovery from the heart of the Peruvian Amazon now unveils a key chapter of the evolutionary saga of these animals. In a paper published February 4, 2015 in the scientific journal Nature, the discovery of three new extinct monkeys from eastern Peru hints strongly that South American monkeys have an African ancestry.
Co-author Dr. Ken Campbell, curator at the Natural History Museum of Los Angeles County (NHM), discovered the first of these fossils in 2010, but because it was so strange to South America, it took an additional two years to realize that it was from a primitive monkey.
Mounting evidence came as a result of further efforts to identify tiny fossils associated with the first find. For many years, Campbell has surveyed remote regions of the Amazon Basin of South America in search for clues to its ancient biological past. “Fossils are scarce and limited to only a few exposed banks along rivers during the dry seasons,” said Campbell. “For much of the year high water levels make paleontological exploration impossible.” In recent years, Campbell has focused his efforts on eastern Peru, working with a team of Argentinian paleontologists expert in the fossils of South America. His goal is to decipher the evolutionary origin of one of the most biologically diverse regions in the world.
The oldest fossil records of New World monkeys (monkeys found in South America and Central America) date back 26 million years. The new fossils indicate that monkeys first arrived in South America at least 36 million years ago. The discovery thus pushes back the colonization of South America by monkeys by approximately 10 million years, and the characteristics of the teeth of these early monkeys provide the first evidence that monkeys actually managed to cross the Atlantic Ocean from Africa.
Reference:
Mariano Bond, Marcelo F. Tejedor, Kenneth E. Campbell, Laura Chornogubsky, Nelson Novo, Francisco Goin. Eocene primates of South America and the African origins of New World monkeys. Nature, 2015; DOI: 10.1038/nature14120
GEE is an education and outreach tool for seismology that aims to make it easy for non-seismologists to retrieve, display and analyze seismic data. It is intended for use in a classroom setting as a supplement to textbook material, which often lacks real world connections. Novices to the world of seismology can use GEE to explore earthquakes they’ve seen in the headlines, keep track of a recording station in their area, look at real-time seismic data, and more!
GEE is comprised of configurable learning “modules” that can be used to convey specific seismological concepts such as wave properties, the structure of the earth, and the differences between P and S waves. The modules provided with GEE are the ones developed for use by the South Carolina Earth Physics Project.
Figure 1 from Manzella et al.: Original and processed snapshot of the video of the Eyjafjallajökull (Iceland) plume as observed on May 4, 2010. White arrows indicate finger positions. Credit: Manzella et al. and Geology
Volcanic ash poses a significant hazard for areas close to volcanoes and for aviation. For example, the 2010 eruption of Eyjafjallajökull, Iceland, clearly demonstrated that even small-to-moderate explosive eruptions, in particular if long-lasting, can paralyze entire sectors of societies, with significant, global-level, economic impacts. In this open-access Geology article, Irene Manzella and colleagues present the first quantitative description of the dynamics of gravitational instabilities and particle aggregation based on the 4 May 2010 eruption.
Their analysis also reveals some important shortcomings in the Volcanic Ash Transport and Dispersal Models (VATDMs) typically used to forecast the dispersal of volcanic ash. In particular, specific processes exist that challenge the view of sedimentation of fine particles from volcanic plumes and that are currently poorly understood: particle aggregation and gravitational instabilities. These appear as particle-rich “fingers” descending from the base of volcanic clouds and have commonly been observed during volcanic explosive eruptions.
Based on direct observations of the 2010 Eyjafjallajökull plume, on the correlation with the associated fallout deposit, and on dedicated laboratory analogue experiments, Irene Manzella and colleagues show how fine ash in these particle-rich fingers settles faster than individual particles and that aggregation and gravitational instabilities are closely related. Both phenomena can significantly contribute to reducing fine-ash lifetime in the atmosphere and, therefore, it is crucial to include them in VATDMs in order to provide accurate forecasting of ash dispersal and sedimentation.
Reference:
I. Manzella, C. Bonadonna, J. C. Phillips, H. Monnard. The role of gravitational instabilities in deposition of volcanic ash. Geology, 2015; DOI: 10.1130/G36252.1
