A file picture taken on March 13, 2009 shows the skeleton of a Cryolophosaurus Ellioti, diplayed at the exhibition “Dinosaurs of Gondwana” at the National Science Museum in Tokyo
The space rock that smashed into Earth 65 million years ago, famously wiping out the dinosaurs, unleashed acid rain that turned the ocean surface into a witches’ brew, researchers said Sunday.
Delving into the riddle of Earth’s last mass extinction, Japanese scientists said the impact instantly vaporised sulphur-rich rock, creating a vast cloud of sulphur trioxide (SO3) gas.
This mixed with water vapour to create sulphuric acid rain, which would have fallen to the planet’s surface within days, acidifying the surface levels of the ocean and killing life therein.
Those species that were able to survive beneath this lethal layer eventually inherited the seas, according to the study which did not delve into the effects on land animals.
“Concentrated sulphuric acid rains and intense ocean acidification by SO3-rich impact vapours resulted in severe damage to the global ecosystem and were probably responsible for the extinction of many species,” the study said.
The great smashup is known as the Cretaceous-Tertiary extinction.
It occurred when an object, believed to be an asteroid some 10 kilometres (six miles) wide, whacked into the Yucatan peninsula in modern-day Mexico.
It left a crater 180 kilometres (110 miles) wide, ignited a firestorm and kicked up a storm of dust that was driven around the world on high winds, according to the mainstream scenario.
Between 60 and 80 percent of species on Earth were wiped out, according to fossil surveys.
Large species suffered especially: dinosaurs which had roamed the land for some 165 million years, were replaced as the terrestrial kings by mammals.
Extinction riddle
Much speculation has been devoted to precisely how the mass die-out happened.
A common theory is that a “nuclear winter” occurred—the dust pall prevented sunlight reaching the surface, causing vegetation to shrivel and die, and dooming the species that depended on them.
Another, fiercely debated, idea adds acid rain to the mix.
Critics say the collision was far likelier to have released sulphur dioxide (SO2) than SO3, the culprit chemical in acid rain. And, they argue, it would have lingered in the stratosphere rather than fallen back to Earth.
Seeking answers, a team led by Sohsuke Ohno of the Planetary Exploration Research Centre in Chiba set up a special lab rig to replicate—on a tiny scale—what happened that fateful day.
They used a laser beam to vaporise a strand of plastic, which released a high-speed blast of plasma and caused a tiny piece of foil, made of the heavy metal tantalum, to smash into a sample of rock.
The heavy foil fragment replicated on a miniscule scale the mass of the asteroid, while the rock was of a similar makeup as the surface where the asteroid struck.
The team caused collisions ranging from 13 to 25 km per second (47,000-90,000 km or 29,000-55,000 miles per hour), and analysed the gas that was released.
The research, reported in the journal Nature Geoscience, showed that SO3 was by far the dominant molecule, not SO2.
The team also carried out a computer simulation of larger silicate particles that would have been ejected by the impact, and found they too played a part.
The articles rapidly bound with the poisonous vapour to become sulphur acid “aerosols” that fell to the surface.
Heavily acidic waters would explain the overwhelming extinction among surface species of plankton called foraminifera.
Foraminifera are single-celled creatures protected by a calcium carbonate shell, which dissolves in acidic water.
The “acid rain” scenario also helps explain other extinction riddles, including why there was a surge in the number of ferns species after the impact. Ferns love acidic, water-logged conditions such as those described in the study.
This image shows a man standing in volanic steam in Antartica. Credit: Peter Convey, British Antartic Survey
An international team of researchers has found evidence that the steam and heat from volcanoes and heated rocks allowed many species of plants and animals to survive past ice ages, helping scientists understand how species respond to climate change. The research could solve a long-running mystery about how some species survived and continued to evolve through past ice ages in parts of the planet covered by glaciers. The team, led by Dr Ceridwen Fraser from the Australian National University and Dr Aleks Terauds from the Australian Antarctic Division, studied tens of thousands of records of Antarctic species, collected over decades by hundreds of researchers, and found there are more species close to volcanoes, and fewer further away.
“Volcanic steam can melt large ice caves under the glaciers, and it can be tens of degrees warmer in there than outside. Caves and warm steam fields would have been great places for species to hang out during ice ages,” Dr Fraser said. “We can learn a lot from looking at the impacts of past climate change as we try to deal with the accelerated change that humans are now causing.” While the study was based on Antarctica, the findings help scientists understand how species survived past ice ages in other icy regions, including in periods when it is thought there was little or no ice-free land on the planet. Antarctica has at least 16 volcanoes which have been active since the last ice age 20,000 years ago. The study examined diversity patterns of mosses, lichens and bugs which are still common in Antarctica today. Professor Peter Convey from the British Antarctic Survey said around 60 per cent of Antarctic invertebrate species are found nowhere else in the world. “They have clearly not arrived on the continent recently, but must have been there for millions of years. How they survived past ice ages – the most recent of which ended less than 20,000 years ago – has long puzzled scientists,” Professor Convey said. Dr Terauds of the Australian Antarctic Division ran the analyses, and says the patterns are striking. “The closer you get to volcanoes, the more species you find. This pattern supports our hypothesis that species have been expanding their ranges and gradually moving out from volcanic areas since the last ice age,” Dr Terauds said. Professor Steven Chown, from Monash University, says the research findings could help guide conservation efforts in Antarctica. “Knowing where the ‘hotspots’ of diversity are will help us to protect them as human-induced environmental changes continue to affect Antarctica,” Professor Chown said. Note : The above story is based on materials provided by Australian National University
Chemical Formula: (Y,Ca,Ce,U,Th)(Nb,Ta,Ti)2O6 Locality: Jolster, Sondfjord, Norway. Name Origin: From the Greek for “friendly to strangers, hospitable,” in allusion to the rare elements that it contains.
Euxenite, which is sometimes named euxenite-(Y) (the Y is for the yttrium), is a mineral that is sometimes called a “trash can mineral”. Because it will accommodate a wide variety of elements in its crystal structure, generally the elements that other minerals do not seem to want, ie the “trash”. For euxenite, these elements are in a group called the rare earths and are sometimes quite valuable, making euxenite a potentially profitable ore. Euxenite’s name is from a Greek phrase meaning “hospitable”, another reference to its . . . accommodating nature.
Euxenite is in a series with the mineral polycrase, another “trash can mineral”. Polycrase is simply richer in titanium as opposed to the niobium rich euxenite. The other elements can be found in both minerals and the structure is basically the same.
Chemical Formula: Na15Ca6(Fe2+,Mn2+)3Zr3[Si25O73](O,OH,H2O)3(OH,Cl)2 Locality: Julianehaab district of Greenland. Name Origin: From the Greek eu – “well” and dialytos – “decomposable.”
Eudialyte, whose name derives from the Greek phrase Εὖ διάλυτος eu dialytos, meaning “well decomposable”, is a somewhat rare, nine member ring cyclosilicate mineral, which forms in alkaline igneous rocks, such as nepheline syenites. Its name alludes to its ready solubility in acid.
Eudialyte was first described in 1819 for an occurrence in nepheline syenite of the Ilimaussaq intrusive complex of southwest Greenland.
Alternative names of eudialyte include: almandine spar, eudalite, Saami blood. Eucolite is the name of an optically negative variety, more accurately the group member: ferrokentbrooksite.
Physical Properties
Cleavage: {0001} Imperfect Color: Pinkish red, Red, Yellow, Yellowish brown, Violet. Density: 2.8 – 3, Average = 2.9 Diaphaneity: Transparent to Translucent Fracture: Uneven – Flat surfaces (not cleavage) fractured in an uneven pattern. Hardness: 5-5.5 – Apatite-Knife Blade Luminescence: Non-fluorescent. Luster: Vitreous (Glassy) Streak: white
Pridoli Series, uppermost of four main divisions of the Silurian System, representing those rocks deposited worldwide during the Pridoli Epoch (423 million to 419.2 million years ago). The series name is derived from the Pridoli area of the Daleje Valley on the outskirts of Prague in the Czech Republic, where about 20 to 50 metres (about 65 to 165 feet) of platy limestone strata rich in cephalopods and bivalves are well-developed.
By international agreement, the base of the Pridoli Series is defined by the first occurrence of the graptolite species Monograptus parultimus in rock exposures at the entrance to the Pozary Quarries, which lie about 1.5 km (about 1 mile) east of Reporyje, outside of southwestern Prague. The M. parultimus biozone, in short, constitutes the global stratotype section and point (GSSP) for the base of the series. In addition, two species of chitinozoans (a type of marine plankton), Urnochitina urna and Fungochitina kosovensis, first occur at or just above the base of the series. The earliest known simple vascular land plants, of the genus Cooksonia, typically occur in the lower portions of the Pridoli Series in many parts of the world. The Pridoli Series is overlain by the Lochkovian Stage, the first stage of the Devonian System. The base of the Lochkovian and the base of the Devonian System automatically define the top of the Pridoli and thus the top of the Silurian System. The Pridoli Series has not been divided into stages and is underlain by the Ludlow Series.
The Ludlow Group are rocks deposited during the Ludlow period of the Silurian in Great Britain. This group contains the following formations in descending order:
Cilestones, Downton Castle sandstones (90 ft./27.7 m),
Ledbury shales 270 ft./83 m),
Upper Ludlow rocks (140 ft./43 m),
Aymestry limestone (up to 40 ft./12.3 m),
Lower Ludlow rocks (350 to 780 ft./108 m-240 m).
The Ludlow group is essentially shaly in character, except towards the top, where the beds become more sandy and pass gradually into the Old Red Sandstone. The Aymestry limestone, which is irregular in thickness, is sometimes absent, and where the underlying Wenlock limestones are absent the shales of the Ludlow group graduate, downwards into the Wenlock shales. The group is typically developed between Ludlow and Aymestrey, and it occurs also in the detached Silurian areas between Dudley and the mouth of the Severn.
The Lower Ludlow rocks are mainly grey, greenish and brown mudstones and sandy and calcareous shales. They contain an abundance of fossils. The series has been zoned by means of the Graptolites by E. M. R. Wood; the following in ascending order, are the zonal forms:
Monograptus vulgaris,
M. Nilssoni,
M. scanicus,
M. tumescens and
M. leintwardinensis.
Cyathaspis ludensis, the earliest British vertebrate fossil, was found in these rocks at Leintwardine in Herefordshire, a noted fossil locality. Trilobites are numerous (Phacops caudatus, Lichas anglicus, Homolonotus delphinocephalus, Calymene Blumenbachii); brachiopods (Leptaena rhomboidalis, Rhynchonella Wilsoni, Atrypa reticularis}, pelecypods (Cardiola interrupts, Ctenodonta sulcata) and gasteropods and cephalopods (many species of Orthoceras and also Gomphoceras, Trochoceras) are well represented. Other fossils are Ceratiocaris , Pterygotus, Protaster, Palaeocoma and Palaeodiscus.
The Upper Ludlow rocks are mainly soft mudstones and shales with some harder sandy beds capable of being worked as building-stones. These sandy beds are often found covered with ripple-marks and annelid tracks; one of the uppermost sandy layers is known as the ” Fucoid bed ” from the abundance of the seaweed-like impressions it bears. At the top of this sub-group, near Ludlow, a brown layer occurs, from a quarter of an inch to 4 in. (63 mm to 100 mm) in thickness, full of the fragmentary remains of fish associated with those of Pterygotus and mollusca. This layer, known as the ” Ludlow Bone bed,” has been traced over a very large area (see Bone Bed). The common fossils include plants (Actinophyllum, Chondrites), ostracods, phyllocarids, eurypterids, trilobites (less common than in the older groups), numerous brachiopods (Lingula minima, Chonetes striatella), gasteropods, pelecypods and cephalopods (Orthoceras bullatum). Fish include Cephalaspis, Cyathaspis, Auchenaspis. The Tilestones, Downton Castle Sandstone and Ledbury shales are occasionally grouped together under the term Downtonian. They are in reality passage beds between the Silurian and Old Red Sandstone, and were originally placed in the latter system by Sir R. I. Murchison. They are mostly grey, yellow or red micaceous, shaly sandstones. Lingula cornea, Platyschisma helicites and numerous phyllocarids and ostracods occur among the fossils.
In Denbighshire and Merionethshire the upper portion of the Denbighshire Grits belongs to this horizon: viz. those from below upwards, the Nantglyn Flags, the Upper Grit beds, the Monograptus leintwardinensis beds and the Dinas Bran beds. In the Silurian area of the Lake district the Coldwell beds, forming the upper part of the Coniston Flags, are the equivalents of the Lower Ludlow; they are succeeded by the Coniston Grits (4,000 ft./1,230 m), the Bannisdale Slates (5200 ft./1,600 m) and the Kirkby Moor Flags (2,000 ft./615 m).
In the Silurian areas of southern Scotland, the Ludlow rocks are represented in the Kirkcudbright Shore and Riccarton district by the Raeberry Castle beds and Balmae Grits (500-750 ft.). In the northern belt Lanarkshire and the Pentland Hillsthe lower portion (or Ludlovian) consists of mudstones, flaggy shales and greywackes; but the upper (or Downtonian) part is made up principally of thick red and yellow sandstones and conglomerates with green mudstones. The Ludlow rocks of Ireland include the ” Salrock beds ” of County Galway and the “Croagmarhin beds” of Dingle promontory.
Note : The above story is based on materials provided by Wikipedia
The Wenlock (seldomly also referred to as Wenlockian) is the second series of the Silurian. It is preceded by the Llandovery series and followed by the Ludlow. Radiometric dates constrain the Wenlockian between 433.4 ± 0.8 and 427.4 ± 0.5 million years ago.
The Wenlock is named after Wenlock Edge, an outcrop of rocks near the town of Much Wenlock in Shropshire (West Midlands, United Kingdom). The name was first used in the term “Wenlock and Dudley rocks” by Roderick Murchison in 1834 to refer to the limestones and underlying shales that underlay what he termed the “Ludlow rocks”. He later modified this term to simply the “Wenlock rocks” in his the Silurian System in 1839.
Definition and subdivision
The Wenlock’s beginning is defined by the lower boundary (or GSSP) of the Sheinwoodian. The end is defined as the base (or GSSP) of the Gorstian.
The Wenlock is divided into the older Sheinwoodian and the younger Homerian stage. The Sheinwoodian lasted from 433.4 ± 0.8 to 430.5 ± 0.7 million years ago. The Homerian lasted from 430.5 ± 0.7 to 427.4 ± 0.5 million years ago.
Note : The above story is based on materials provided by Wikipedia
In geology, the Llandovery Group refers to the lowest division of the Silurian period (Upper Silurian) in Britain. It is named after the town of Llandovery in Wales, although Charles Lapworth had proposed the name Valentian (from the Roman British province of Valentia) for this group in 1879. It includes the Tarannon Shales (1000-1500 ft.), Upper Llandovery and May Hill Sandstone (800 ft.), Lower Llandovery, (600-1500 ft.)
The Lower Llandovery rocks consist of conglomerates, sandstones and slaty beds. At Llandovery they rest upon Ordovician rocks. These rocks occur with a narrow crop in Pembrokeshire, which curves round through Llandovery, and in the Rhayader district they reach a considerable thickness. They also occur in Ceredigion and Carmarthenshire.
The Upper Llandovery has local lenticular developments of shelly limestone (Norbury, Hollies and Pentamerus limestones). It occurs with a narrow outcrop in Carmarthenshire at the base of the Silurian, disappearing beneath the Old Red Sandstone westward to reappear in Pembrokeshire; north-eastward the outcrop extends to the Long Mynd, which the conglomerate wraps round. As it is followed along the crop it rests upon the Lower Llandovery, Caradog, Llandeilo, Cambrian and pre-Cambrian rocks. The fossils include the trilobites Phacops caudata, Encrinurus punctatus and Calymene blumenbachis; the brachiopods Pentamerus oblongus, Orthis calligramma and Atrypa reticularis; the corals Favosites and Lindostroemia; and the zonal graptolites Rastriles maximus and Monograptus spinigerus.
The Tarannon shales, grey and blue slates, designated by Adam Sedgwick the Paste Rock, is traceable from Conwy into Carmarthenshire; in Ceredigion, there are gritty beds; and in the neighbourhood of Builth, soft dark shales. The group is poor in fossils, with the exception of graptolites; of these Cyrtograptus grayae and Monograptus exiguus are zonal forms. The Tarannon group is represented by the Rhayader Pale Shales in Powys; in the Moffat Silurian belt in south Scotland by a thick development, including the Hawick rocks and Ardwell Beds, and the Queensberry Group or Gala; in the Girvan area, by the Drumyork Flags, Bargany Group and Penkill Group; and in Ireland by the Treveshilly Shales of Strangford Lough, and the shales of Salterstown, Co. Louth.
The Upper and Lower Llandovery rocks are represented in descending order by the Pale Shales, Graptolite Shales, Grey Slates and Corwen Grit of Meirionnydd and Denbighshire. In the Lake district the lower part of the Stockdale shales (Skelgill beds) is of Llandovery age. In the Girvan area to the north their place is taken by the Camregan, Shaugh Hill and Mullock Hill groups. In Ireland the Llandovery rocks are represented by the Anascaul Slates of the Dingle promontory, by the Owenduff and Gowlaun Grits, Co. Galway, by the Upper Pomeroy Beds, by the Uggool and Ballaghaderin Beds, Co. Mayo, and by rocks of this age in Coalpit Bay and Slieve Felim Mountains.
Economic deposits in Llandovery rocks include slate pencils (Teesdale), building stone, flag-stone, road metal and lime.
Note : The above story is based on materials provided by Wikipedia
The new dinosaur species is estimated up to 10 meters long and 4-5 tons. Credit: Christophe Hendrickx; CC-BY
A new dinosaur species found in Portugal may be the largest land predator discovered in Europe, as well as one of the largest carnivorous dinosaurs from the Jurassic, according to a paper published in PLOS ONE on March 5, 2014 by co-authors Christophe Hendrickx and Octavio Mateus from Universidade Nova de Lisboa and Museu da Lourinhã.
Scientists discovered bones belonging to this dinosaur north of Lisbon. They were originally believed to be Torvosaurus tanneri, a dinosaur species from North America. Closer comparison of the shin bone, upper jawbone, teeth, and partial tail vertebrae suggest to the authors that it may warrant a new species name, Torvosaurus gurneyi.
T. gurneyi had blade-shaped teeth up to 10 cm long, which indicates it may have been at the top of the food chain in the Iberian Peninsula roughly 150 million years ago. The scientists estimate that the dinosaur could reach 10 meters long and weigh around 4 to 5 tons. The number of teeth, as well as size and shape of the mouth, may differentiate the European and the American Torvosaurus. The fossil of the upper jaw of T. tanneri has 11 or more teeth, while T. gurneyi has fewer than 11. Additionally, the mouth bones have a different shape and structure. The new dinosaur is the second species of Torvosaurus to be named.
“This is not the largest predatory dinosaur we know. Tyrannosaurus, Carcharodontosaurus, and Giganotosaurus from the Cretaceous were bigger animals,” said Christophe Hendrickx. “With a skull of 115 cm, Torvosaurus gurneyi was however one of the largest terrestrial carnivores at this epoch, and an active predator that hunted other large dinosaurs, as evidenced by blade shape teeth up to 10 cm.” Fossil evidences of closely related dinosaurs suggest that this large predator may have already been covered with proto-feathers. Recently described dinosaur embryos from Portugal are also ascribed to the new species of Torvosaurus.
Note : The above story is based on materials provided by PLOS.
Optical microscopy image in cross polarized light of a natural olivine polycrystal (Oman mylonite). Credit: S. Demouchy, Montpellier
Earth’s mantle is a solid layer that undergoes slow, continuous convective motion. But how do these rocks deform, thus making such motion possible, given that minerals such as olivine (the main constituent of the upper mantle) do not exhibit enough defects in their crystal lattice to explain the deformations observed in nature? A team led by the Unité Matériaux et Transformations (CNRS/Université Lille 1/Ecole Nationale Supérieure de Chimie de Lille) has provided an unexpected answer to this question.
It involves little known and hitherto neglected crystal defects, known as ‘disclinations’, which are located at the boundaries between the mineral grains that make up rocks. Focusing on olivine, the researchers have for the first time managed to observe such defects and model the behavior of grain boundaries when subjected to a mechanical stress.
The findings, which have just been published in Nature, go well beyond the scope of the geosciences: they provide a new, extremely powerful tool for the study of the dynamics of solids and for the materials sciences in general.
Earth continuously releases its heat via convective motion in Earth’s mantle, which underlies the crust. Understanding this convection is therefore fundamental to the study of plate tectonics. The mantle is made up of solid rocks. In order for convective motion to occur, it must be possible for the crystal lattice of these rocks to deform. Until now, this was a paradox that science was unable to fully resolve. While defects in the crystal lattice, called dislocations, provide a very good explanation of the plasticity of metals, they are insufficient to explain the deformations undergone by certain mantle rocks.
The researchers suspected that the solution was to be found at the boundaries between the mineral grains that make up rocks. However, they lacked the conceptual tools needed to describe and model the role played by these boundaries in the plasticity of rocks.
Researchers at the Unité Matériaux et Transformations (CNRS/Université Lille 1/Ecole Nationale Supérieure de Chimie de Lille) in collaboration with researchers at the Laboratoire Géosciences Montpellier (CNRS/Université Montpellier 2) and the Laboratoire d’Etude des Microstructures et de Mécanique des Matériaux (CNRS/Université de Lorraine/Arts et Métiers ParisTech/Ecole Nationale d’Ingénieurs de Metz) have now explained this role. They have shown that the crystal lattice of the grain boundaries exhibits highly specific defects known as ‘disclinations’, which had hitherto been neglected. The researchers succeeded in observing them for the first time in samples of olivine (which makes up as much as 60% of the upper mantle) by using an electron microscope and specific image processing. They even went further: based on a mathematical model, they showed that these disclinations provided an explanation for the plasticity of olivine. When mechanical stress is applied, the disclinations enable the grain boundaries to move, thus allowing olivine to deform in any direction. Flow in the mantle is thus no longer incompatible with its rigidity.
This research goes beyond explaining the plasticity of rocks in Earth’s mantle: it is a major step forward in materials science. Consideration of disclinations should provide scientists with a new tool to explain many phenomena related to the mechanics of solids. The scientists intend to continue their research into the structure of grain boundaries, not only in other minerals but also in other solids such as metals.
Note : The above story is based on materials provided by CNRS.
NASA images used in a photo composite. Credit: Christine Daniloff/MIT
Earth’s magnetic field, or magnetosphere, stretches from the planet’s core out into space, where it meets the solar wind, a stream of charged particles emitted by the sun. For the most part, the magnetosphere acts as a shield to protect Earth from this high-energy solar activity.
But when this field comes into contact with the sun’s magnetic field — a process called “magnetic reconnection” — powerful electrical currents from the sun can stream into Earth’s atmosphere, whipping up geomagnetic storms and space weather phenomena that can affect high-altitude aircraft, as well as astronauts on the International Space Station.
Now scientists at MIT and NASA have identified a process in Earth’s magnetosphere that reinforces its shielding effect, keeping incoming solar energy at bay.
By combining observations from the ground and in space, the team observed a plume of low-energy plasma particles that essentially hitches a ride along magnetic field lines — streaming from Earth’s lower atmosphere up to the point, tens of thousands of kilometers above the surface, where the planet’s magnetic field connects with that of the sun. In this region, which the scientists call the “merging point,” the presence of cold, dense plasma slows magnetic reconnection, blunting the sun’s effects on Earth.
“The Earth’s magnetic field protects life on the surface from the full impact of these solar outbursts,” says John Foster, associate director of MIT’s Haystack Observatory. “Reconnection strips away some of our magnetic shield and lets energy leak in, giving us large, violent storms. These plasmas get pulled into space and slow down the reconnection process, so the impact of the sun on the Earth is less violent.”
Foster and his colleagues publish their results in this week’s issue of Science. The team includes Philip Erickson, principal research scientist at Haystack Observatory, as well as Brian Walsh and David Sibeck at NASA’s Goddard Space Flight Center.
For more than a decade, scientists at Haystack Observatory have studied plasma plume phenomena using a ground-based technique called GPS-TEC, in which scientists analyze radio signals transmitted from GPS satellites to more than 1,000 receivers on the ground. Large space-weather events, such as geomagnetic storms, can alter the incoming radio waves — a distortion that scientists can use to determine the concentration of plasma particles in the upper atmosphere. Using this data, they can produce two-dimensional global maps of atmospheric phenomena, such as plasma plumes.
These ground-based observations have helped shed light on key characteristics of these plumes, such as how often they occur, and what makes some plumes stronger than others. But as Foster notes, this two-dimensional mapping technique gives an estimate only of what space weather might look like in the low-altitude regions of the magnetosphere. To get a more precise, three-dimensional picture of the entire magnetosphere would require observations directly from space.
Toward this end, Foster approached Walsh with data showing a plasma plume emanating from Earth’s surface, and extending up into the lower layers of the magnetosphere, during a moderate solar storm in January 2013. Walsh checked the date against the orbital trajectories of three spacecraft that have been circling the Earth to study auroras in the atmosphere.
As it turns out, all three spacecraft crossed the point in the magnetosphere at which Foster had detected a plasma plume from the ground. The team analyzed data from each spacecraft, and found that the same cold, dense plasma plume stretched all the way up to where the solar storm made contact with Earth’s magnetic field.
A river of plasma
Foster says the observations from space validate measurements from the ground. What’s more, the combination of space- and ground-based data give a highly detailed picture of a natural defensive mechanism in Earth’s magnetosphere.
“This higher-density, cold plasma changes about every plasma physics process it comes in contact with,” Foster says. “It slows down reconnection, and it can contribute to the generation of waves that, in turn, accelerate particles in other parts of the magnetosphere. So it’s a recirculation process, and really fascinating.”
Foster likens this plume phenomenon to a “river of particles,” and says it is not unlike the Gulf Stream, a powerful ocean current that influences the temperature and other properties of surrounding waters. On an atmospheric scale, he says, plasma particles can behave in a similar way, redistributing throughout the atmosphere to form plumes that “flow through a huge circulation system, with a lot of different consequences.”
“What these types of studies are showing is just how dynamic this entire system is,” Foster adds.
Note : The above story is based on materials provided by Massachusetts Institute of Technology.
Euclase Alto do Giz pegmatite, Equador, Rio Grande do Norte, Brazil Miniature, 4.2 x 2.4 x 2.2 cm “Courtesy of Rob Lavinsky, The Arkenstone, www.iRocks.com”
Chemical Formula: BeAl(SiO4)(OH) Locality: Orenburg district in the southern Urals, Russia. Name Origin: From the Greek eu – “well” and klasis – “breaking.”Euclase is a beryllium aluminium hydroxide silicate mineral (BeAl(SiO4)(OH)). It crystallizes in the monoclinic crystal system and is typically massive to fibrous as well as in slender prismatic crystals. It is related to beryl (Be3Al2Si6O18) and other beryllium minerals. It is a product of the decomposition of beryl in pegmatites.Euclase crystals are noted for their blue color, ranging from very pale to dark blue. The mineral may also be colorless, white, or light green. Cleavage is perfect, parallel to the clinopinacoid, and this suggested to René Just Haüy the name euclase, from the Greek εὖ, easily, and κλάσις, fracture. The ready cleavage renders the crystals fragile with a tendency to chip, and thus detracts from its use for personal ornament. When cut it resembles certain kinds of beryl and topaz, from which it may be distinguished by its specific gravity (3.1). Its hardness (7.5) is similar to beryl (7.5 – 8), and a bit less than that of topaz (8).It was first reported in 1792 from the Orenburg district in the southern Urals, Russia, where it is found with topaz and chrysoberyl in the gold-bearing gravels of the Sanarka (nowadays probably, Sakmara River, Mednogorsk district, Orenburgskaya Oblast’). Its type locality is Ouro Prêto, Minas Gerais, Southeast Region, Brazil, where it occurs with topaz. It is found rarely in the mica-schist of the Rauris in the Austrian Alps.
The magnetite database can help exploration geologists distinguish between barren and mineralised areas of land. Credit: David Clarke
Finding ways to target mineral deposits in remote and deeply covered areas, such as in WA’s often thick regolith cover, has been a major motivating factor in collaborative research between Australian and US scientists.
Exploring the use of magnetite as a pathfinder mineral, the study involved the CSIRO Minerals Down Under Flagship, University of WA’s Centre for Exploration Targeting and the US Geological Survey at Denver’s Central Mineral and Environmental Resources Science Centre.
Study co-author Patrick Nadoll, who is based at Kensington’s CSIRO Earth Science Resource Engineering, says a steadily growing magnetite chemistry database is showing distinctive compositional trends that can discriminate between hydrothermal (formed from water) and igneous (formed from lava or magma) magnetite.
“This helps exploration geologists find mineral deposits distal to the main mineralisation,” he says.
“The composition of igneous and hydrothermal magnetite is governed by several chemical and physical factors, such as temperature and fluid composition.
“Variations in the concentrations of key minor and trace elements represent a compositional signature that can fingerprint host rocks and mineral deposits.”
Main discriminator elements for magnetite are magnesium, aluminium, titanium, vanadium, chromium, manganese, cobalt, nickel, zinc, and gallium which are commonly present at detectable levels (10 to 1000 parts per million).
They display systematic variations across different types of mineral deposits and can also help to differentiate barren from mineralised areas.
“The use of statistical data exploration has been particularly helpful to find trends and patterns in large databases,” Dr Nadoll says.
“And the occurrence, abundance and composition of mineral inclusions in magnetite can also be a useful guide for exploration.
“For example, sulfide inclusions in magnetite are indicative for hydrothermal magnetite from sulfidic hydrothermal ore deposits such as skarn or porphyry deposits.”
Several differences between magnetite minor and trace element data for magnetite were found for different locations around the world—but Dr Nadoll says the variations are controlled by different formation conditions rather than representing a geographical signature.
“Overall, hydrothermal magnetite from a specific mineral deposit type and igneous magnetite from a specific host rock show a characteristic range of minor and trace element concentrations, which is their compositional signature,” he says.
“Magnetite from magnesian skarn deposits in the US will have similar compositional signatures to magnetite from the same deposit type in Indonesia.”
Following on from the research, Dr Nadoll says magnetite from glacigenic or stream sediments, or from regolith cover, can serve as an indicator for mineral exploration.
Note : The above story is based on materials provided by Science Network WA
This illustration shows the plumbing system beneath the Sierra Negra volcano. Credit: Cynthia Ebinger, University of Rochester
The Galápagos Islands are home to some of the most active volcanoes in the world, with more than 50 eruptions in the last 200 years. Yet until recently, scientists knew far more about the history of finches, tortoises, and iguanas than of the volcanoes on which these unusual fauna had evolved.
Now research out of the University of Rochester is providing a better picture of the subterranean plumbing system that feeds the Galápagos volcanoes, as well as a major difference with another Pacific Island chain — the Hawaiian Islands. The findings have been published in the Journal of Geophysical Research: Solid Earth.
“With a better understanding of what’s beneath the volcanoes, we’ll now be able to more accurately measure underground activity,” said Cynthia Ebinger, a professor of earth and environmental sciences. “That should help us better anticipate earthquakes and eruptions, and mitigate the hazards associated with them.”
Ebinger’s team, which included Mario Ruiz from the Instituto Geofisico Escuela Politecnica Nacional in Quito, Ecuador, buried 15 seismometers around Sierra Negra, the largest and most active volcano in the Galápagos. The equipment was used to measure the velocity and direction of different sound waves generated by earthquakes as they traveled under Sierra Negra. Since the behavior of the waves varies according to the temperature and types of material they’re passing through, the data collected allowed the researchers to construct a 3D image of the plumbing system beneath the volcano, using a technique similar to a CAT-scan.
Five kilometers down is the beginning of a large magma chamber lying partially within old oceanic crust that had been buried by more than 8 km of eruptive rock layers. And the oceanic crust has what appears to be a thick underplating of rock formed when magma that was working its way toward the surface became trapped under the crust and cooled — very much like the processes that occur under the Hawaiian Islands.
The researchers found that the Galápagos had something else in common with the Hawaiian Islands. Their data suggest the presence of a large chamber filled with crystal-mush magma — cooled magma that includes crystallized minerals.
The Galápagos Islands formed from a hotspot of magma located in an oceanic plate — called Nazca — about 600 miles of Ecuador, in a process very similar to how the Hawaiian Islands were created. Magma rising from the hotspot eventually hardened into an island. Then, as the Nazca plate inched its way westward, new islands formed in the same manner, resulting in the present-day Galápagos Archipelago.
While there are several similarities between the two island chains, Ebinger uncovered a major difference. The older volcanos in the Hawaiian Islands are dormant, because they’ve moved away from the hotspot that provided the source of magma. In the Galápagos, the volcanoes are connected to the same plumbing system. By studying satellite views of the volcanoes, Ebinger and colleagues noticed that, as the magma would sink in one, it would rise in a different volcano — indicating that that some of the youngest volcanoes had magma connections, even if those connections were temporary.
“Not only do we have a better understanding of the physical properties of Sierra Negra,” said Ebinger, “we have increased out knowledge of island volcano systems, in general.”
The Galápagos Islands are home to some of the most active volcanoes in the world, with more than 50 eruptions in the last 200 years. Yet until recently, scientists knew far more about the history of finches, tortoises, and iguanas than of the volcanoes on which these unusual fauna had evolved.
Now research out of the University of Rochester is providing a better picture of the subterranean plumbing system that feeds the Galápagos volcanoes, as well as a major difference with another Pacific Island chain — the Hawaiian Islands.
Note : The above story is based on materials provided by University of Rochester.
Anchiornis huxleyi Image: Michael DiGiorgio, Yale University
Paleontologists studying fossilized feathers have proposed that the shapes of certain microscopic structures inside the feathers can tell us the color of ancient birds. But new research from North Carolina State University demonstrates that it is not yet possible to tell if these structures — thought to be melanosomes — are what they seem, or if they are merely the remnants of ancient bacteria.
Melanosomes are small, pigment-filled sacs located inside the cells of feathers and other pigmented tissues of vertebrates. They contain melanin, which can give feathers colors ranging from brownish-red to gray to solid black. Melanosomes are either oblong or round in shape, and the identification of these small bodies in preserved feathers has led to speculation about the physiology, habitats, coloration and lifestyles of the extinct animals, including dinosaurs, that once possessed them.
But melanosomes are not the only round and oblong microscopic structures that might show up in fossilized feathers. In fact, the microbes that drove the decomposition of the animal prior to fossilization share the same size and shape as melanosomes, and they would also be present in feathers during decay.
Alison Moyer, a Ph.D. candidate in paleontology at NC State, wanted to find out whether these structures could be definitively identified as either melanosome or microbe. Using black and brown chicken feathers — chickens are one of the closest living relatives to both dinosaurs and ancient birds — Moyer grew bacteria over them to replicate what we see in the fossil record. She used three different types of microscopy to examine the patterns of biofilm growth, and then compared those structures to melanosomes inside of chicken feathers that she had sliced open. Finally, she compared both microbes and actual melanosomes to structures in a fossilized feather from Gansus yumenensis, an avian dinosaur that lived about 120 million years ago, and to published images of fossil “melanosomes” by others. Her findings led to more questions.
“These structures could be original to the bird, or they could be a biofilm which has grown over and degraded the feather — if the latter, they would also produce round or elongated structures that are not melanosomes,” Moyer says. “Melanosomes are embedded in keratin, which is a very tough protein, so they’re hard to see unless there’s been some degradation. But the bacteria are doing the degrading, and so that may be what we’re seeing, rather than the melanosome itself. It’s impossible to say with certainty what these structures are without more data, including fine scale chemical data.”
The research appears online in Scientific Reports. Possible next steps for Moyer include testing for the presence of keratin or bacteria within the fossils, by looking for their molecular signals.
“The technology that we have available to us as paleontologists now is amazing, and will make it much easier to test all of the hypotheses we develop about these fossils,” Moyer says. “In the meantime, perhaps we can establish some basic criteria for identifying these structures as melanosomes, such as whether they’re found within the feather’s interior, or externally.”
The research was funded in part by the National Science Foundation and the David and Lucille Packard foundation. The fossil feather was provided by the Gansu Geological Museum in Lanzhou, Gansu, China.
Note : The above story is based on materials provided by North Carolina State University.
Chemical Formula: Co3(AsO4)2 · 8H2O Locality: Grube Daniel, Schneeberg, Germany. Name Origin: Named from the Greek, erythros for “red.”
Erythrite or red cobalt is a secondary hydrated cobalt arsenate mineral with the formula (Co3(AsO4)2 · 8H2O). Erythrite and annabergite (Ni3(AsO4)2·8H2O) (nickel arsenate) form a complete series with the general formula (Co,Ni)3(AsO4)2·8H2O.
Erythrite crystallizes in the monoclinic system and forms prismatic crystals. The color is crimson to pink and occurs as a secondary coating known as cobalt bloom on cobalt arsenide minerals. Well-formed crystals are rare, with most of the mineral manifesting in crusts or small reniform aggregates.
Erythrite was first described in 1832 for an occurrence in Grube Daniel, Schneeberg, Saxony, and takes its name from the Greek έρυθρος (erythros), meaning red. Historically, erythrite itself has not been an economically important mineral, but the prospector may use it as a guide to associated cobalt and native silver.
Erythrite occurs as a secondary mineral in the oxide zone of Co–Ni–As bearing mineral deposits. It occurs in association with cobaltite, skutterudite, symplesite, roselite-beta, scorodite, pharmacosiderite, adamite, morenosite, retgersite, and malachite.
Notable localities are Cobalt, Ontario; Schneeberg, Saxony, Germany; Joachimsthal, Czech Republic; Cornwall, England; Bou Azzer, Morocco; the Blackbird mine, Lemhi County, Idaho; Sara Alicia mine, near Alamos, Sonora, Mexico; Mt. Cobalt, Queensland and the Dome Rock copper mine, Mingary, South Australia.
Asthenosphere and lithospheric plate Credit: Nicholas Schmerr/University of Maryland
The Earth’s outer layer is made up of a series of moving, interacting plates whose motion at the surface generates earthquakes, creates volcanoes and builds mountains. Geoscientists have long sought to understand the plates’ fundamental properties and the mechanisms that cause them to move and drift, and the questions have become the subjects of lively debate.
A study published online Feb. 27 by the journal Science is a significant step toward answering those questions.
Researchers led by Caroline Beghein, assistant professor of earth, planetary and space sciences in UCLA’s College of Letters and Science, used a technique called seismic tomography to study the structure of the Pacific Plate — one of eight to 12 major plates at the surface of the Earth. The technique enabled them to determine the plate’s thickness, and to image the interior of the plate and the underlying mantle (the layer between the Earth’s crust and outer core), which they were able to relate to the direction of flow of rocks in the mantle.
“Rocks deform and flow slowly inside the Earth’s mantle, which makes the plates move at the surface,” said Beghein, the paper’s lead author. “Our research enables us to image the interior of the plate and helps us figure out how it formed and evolved.” The findings might apply to other oceanic plates as well.
Even with the new findings, Beghein said, the fundamental properties of plates “are still somewhat enigmatic.”
Seismic tomography is similar to commonly used medical imaging techniques like computed tomography, or CT, scans. But instead of using X-rays, seismic tomography employs recordings of the seismic waves generated by earthquakes, allowing scientists to detect variations in the speed of seismic waves inside the Earth. Those variations can reveal different layers within the mantle, and can help scientists determine the temperature and chemistry of the mantle rocks by comparing observed variations in wave speed with predictions from other types of geophysical data.
Seismologists often use other types of seismic data to identify this layering: They detect seismic waves that bounce off the interface that separates two layers. In their study, Beghein and co-authors compared the layering they observed using seismic tomography with the layers revealed by these other types of data. Comparing results from the different methods is a continuing challenge for geoscientists, but it is an important part of helping them understand the Earth’s structure.
“We overcame this challenge by trying to push the observational science to the highest resolutions, allowing us to more readily compare observations across datasets,” said Nicholas Schmerr, the study’s co-author and an assistant research scientist in geology at the University of Maryland.
The researchers were the first to discover that the Pacific Plate is formed by a combination of mechanisms: The plate thickens as the rocks of the mantle cool, the chemical makeup of the rocks that form the plate changes with depth, and the mechanical behavior of the rocks change with depth and their proximity to where the plate is being formed at the mid-ocean ridge.
“By modeling the behavior of seismic waves in Earth’s mantle, we discovered a transition inside the plate from the top, where the rocks didn’t deform or flow very much, to the bottom of the plate, where they are more strongly deformed by tectonic forces,” Beghein said. “This transition corresponds to a boundary between the layers that we can image with seismology and that we attribute to changes in rock composition.”
Oceanic plates form at ocean ridges and disappear into the Earth’s mantle, a process known as subduction. Among geoscientists, there is still considerable debate about what drives this evolution. Beghein and her research team advanced our understanding of how oceanic plates form and evolve as they age by using and comparing two sets of seismic data; the study revealed the presence of a compositional boundary inside the plate that appears to be linked to the formation of the plate itself.
Other co-authors of the research are Kaiqing Yuan and Zheng Xing, graduate students in UCLA’s Department of Earth, Planetary and Space Sciences.
Note : The above story is based on materials provided by University of California – Los Angeles.
This is the fossil of the salamander Chunerpeton showing not only the preserved skeleton but also the skin and even external gills. Credit: Society of Vertebrate Paleontology
Over the last two decades, huge numbers of fossils have been collected from the western Liaoning Province and adjacent parts of northeastern China, including exceptionally preserved feathered dinosaurs, early birds, and mammals. Most of these specimens are from the Cretaceous Period, including the famous Jehol Biota.
However, in recent years many fossils have emerged from sites that are 30 million years earlier, from the Middle-Upper Jurassic Period, providing an exceptional window on life approximately 160 million years ago. A new paper published in latest issue of the Journal of Vertebrate Paleontology shows that several of these Jurassic sites are linked together by shared species and can be recognized as representing a single fossil fauna and flora, containing superbly preserved specimens of a diverse group of amphibian, mammal, and reptile species.
This fossil assemblage, newly named the Daohugou Biota after a village near one of the major localities in Inner Mongolia, China, dates from a time when many important vertebrate groups, including our own group, mammals, were undergoing evolutionary diversification. The Daohugou Biota makes an immense contribution to our understanding of vertebrate evolution during this period, with such notable creatures as the oldest known gliding mammal, another early mammal that may have swum with a beaver-like tail, the oldest dinosaurs preserved with feathers, and a pterosaur that represents an important transitional form between two major groups. As described by Dr. Corwin Sullivan, lead author of the study, “The Daohugou Biota gives us a look at a rarely glimpsed side of the Middle to Late Jurassic — not a parade of galumphing giants, but an assemblage of quirky little creatures like feathered dinosaurs, pterosaurs with ‘advanced’ heads on ‘primitive’ bodies, and the Mesozoic equivalent of a flying squirrel.”
Almost more impressive than the diversity of the biota is the preservation of many of the vertebrate specimens, including complete or nearly-complete skeletons associated with preserved soft tissues such as feathers, fur, skin or even, in some of the salamanders, external gills. Dr Yuan Wang, co-author of the study, explained, “The Daohugou amphibians are crucially important in the study of the phylogeny and early radiation of modern amphibian groups.”
Dr. Paul Barrett, dinosaur researcher at the Natural History Museum, London, who was not involved with the study, commented, “Daohugou is proving to be one of the key sites for understanding the evolution of feathered dinosaurs, early mammals, and flying reptiles, due largely to the fantastic levels of preservation. Many of the fossils are stunning and offer vast amounts of information. There are only a handful of similar sites elsewhere in the world and this article represents the first comprehensive attempt to draw all of the relevant information together into a single benchmark paper.” Because the Daohugou Biota and the much better studied Jehol Biota are similar in preservational mode and geographic location, but separated by tens of millions of years, they give palaeontologists an outstanding, even unique, opportunity to study changes in the fauna of this region over a significant span of geological time and an important period in vertebrate evolution. As Dr. Sullivan further remarked, “The Cretaceous feathered dinosaurs of northeastern China have been astonishing palaeontologists and the public for almost two decades now, and the Daohugou Biota preserves their Jurassic counterparts in the same region. As prequels go, it’s pretty exciting.”
Note : The above story is based on materials provided by Society of Vertebrate Paleontology.
Well-developed crystals of epidote, {Ca2}{Al2Fe3+}(Si2O7)(SiO4)O(OH), crystallizing in the monoclinic system, are of frequent occurrence: they are commonly prismatic in habit, the direction of elongation being perpendicular to the single plane of symmetry. The faces are often deeply striated and crystals are often twinned. Many of the characters of the mineral vary with the amount of iron present for instance, the color, the optical constants, and the specific gravity. The color is green, grey, brown or nearly black, but usually a characteristic shade of yellowish-green or pistachio-green. It displays strong pleochroism, the pleochroic colors being usually green, yellow and brown. Clinozoisite is green, white or pale rose-red group species containing very little iron, thus having the same chemical composition as the orthorhombic mineral zoisite. The name is derived from the Greek word “epidosis” (επίδοσις) which means “addition” in allusion to one side of the ideal prism being longer than the other.
Epidote is an abundant rock-forming mineral, but one of secondary origin. It occurs in marble and schistose rocks of metamorphic origin. It is also a product of hydrothermal alteration of various minerals (feldspars, micas, pyroxenes, amphiboles, garnets, and others) composing igneous rocks. A rock composed of quartz and epidote is known as epidosite. Well-developed crystals are found at many localities: Knappenwand, near the Großvenediger in the Untersulzbachthal in Salzburg, as magnificent, dark green crystals of long prismatic habit in cavities in epidote schist, with asbestos, adularia, calcite, and apatite; the Ala valley and Traversella in Piedmont; Arendal in Norway; Le Bourg-d’Oisans in Dauphiné; Haddam in Connecticut; Prince of Wales Island in Alaska, here as large, dark green, tabular crystals with copper ores in metamorphosed limestone.
The perfectly transparent, dark green crystals from the Knappenwand and from Brazil have occasionally been cut as gemstones.
Physical Properties
Cleavage: {001} Perfect Color: Yellowish green, Brownish green, Black, Yellow, Gray. Density: 3.3 – 3.6, Average = 3.45 Diaphaneity: Transparent to translucent to opaque Fracture: Regular – Flat surfaces (not cleavage) fractured in a regular pattern. Hardness: 7 – Quartz Luminescence: Non-fluorescent. Luster: Vitreous (Glassy) Streak: grayish white
The Silurian is a geologic period and system that extends from the end of the Ordovician Period, about 443.4 ± 1.5 million years ago (mya), to the beginning of the Devonian Period, about 419.2 ± 3.2 mya (ICS, 2004). As with other geologic periods, the rock beds that define the period’s start and end are well identified, but the exact dates are uncertain by several million years. The base of the Silurian is set at a major extinction event when 60% of marine species were wiped out. See Ordovician-Silurian extinction events.
A significant evolutionary milestone during the Silurian was the diversification of jawed and bony fish. Life also began to appear on land in the form of small, moss-like, vascular plants which grew beside lakes, streams, and coastlines, and also in the form of small terrestrial arthropods. However, terrestrial life would not greatly diversify and affect the landscape until the Devonian.
The Silurian system was first identified by British geologist Sir Roderick Impey Murchison, who was examining fossil-bearing sedimentary rock strata in south Wales in the early 1830s. He named the sequences for a Celtic tribe of Wales, the Silures, inspired by his friend Adam Sedgwick, who had named the period of his study the Cambrian, the Latin name for Wales. This naming does not indicate any correlation between the occurrence of the Silurian rocks and the land inhabited by the Silures; cf. Geology of Wales, Tribes of Wales. In 1835 the two men presented a joint paper, under the title On the Silurian and Cambrian Systems, Exhibiting the Order in which the Older Sedimentary Strata Succeed each other in England and Wales, which was the germ of the modern geological time scale. As it was first identified, the “Silurian” series when traced farther afield quickly came to overlap Sedgwick’s “Cambrian” sequence, however, provoking furious disagreements that ended the friendship. Charles Lapworth resolved the conflict by defining a new Ordovician system including the contested beds. An early alternative name for the Silurian was “Gotlandian” after the strata of the Baltic island of Gotland.
The French geologist Joachim Barrande, building on Murchison’s work, used the term Silurian in a more comprehensive sense than was justified by subsequent knowledge. He divided the Silurian rocks of Bohemia into eight stages. His interpretation was questioned in 1854 by Edward Forbes, and the later stages of Barrande, F, G and H, have since been shown to be Devonian. Despite these modifications in the original groupings of the strata, it is recognized that Barrande established Bohemia as a classic ground for the study of the earliest fossils.
Subdivisions
Llandovery
The Llandovery Epoch lasted from 443.4 ± 1.5 to 433.4 ± 2.8 mya, and is subdivided into three stages: the Rhuddanian, lasting until 440.8 million years ago, the Aeronian, lasting to 438.5 million years ago, and the Telychian. The epoch is named for the town of Llandovery in Carmarthenshire, Wales.
Wenlock
The Wenlock, which lasted from 433.4 ± 1.5 to 427.4 ± 2.8 mya, is subdivided into the Sheinwoodian (to 430.5 million years ago) and Homerian ages. It is named after Wenlock Edge in Shropshire, England. During the Wenlock, the oldest known tracheophytes of the genus Cooksonia, appear. The complexity of slightly younger Gondwana plants like Baragwanathia indicates a much longer history for vascular plants, perhaps extending into the early Silurian or even Ordovician. See Evolutionary history of plants. The first terrestrial animals also appear in the Wenlock, represented by air-breathing millipedes from Scotland.
Ludlow
The Ludlow, lasting from 427.4 ± 1.5 to 423 ± 2.8 mya, comprises the Gorstian stage, lasting until 425.6 million years ago, and the Ludfordian stage. It is named for the town of Ludlow in Shropshire, England.
Přídolí
The Pridoli, lasting from 423 ± 1.5 to 419.2 ± 2.8 mya, is the final and shortest epoch of the Silurian. It is named after one locality at the Homolka a Přídolí nature reserve near the Prague suburb Slivenec in the Czech Republic. Přídolí is the old name of a cadastral field area.
Regional stages
In North America a different suite of regional stages is sometimes used:
With the supercontinent Gondwana covering the equator and much of the southern hemisphere, a large ocean occupied most of the northern half of the globe. The high sea levels of the Silurian and the relatively flat land (with few significant mountain belts) resulted in a number of island chains, and thus a rich diversity of environmental settings.
During the Silurian, Gondwana continued a slow southward drift to high southern latitudes, but there is evidence that the Silurian icecaps were less extensive than those of the late Ordovician glaciation. The southern continents remained united during this period. The melting of icecaps and glaciers contributed to a rise in sea level, recognizable from the fact that Silurian sediments overlie eroded Ordovician sediments, forming an unconformity. The continents of Avalonia, Baltica, and Laurentia drifted together near the equator, starting the formation of a second supercontinent known as Euramerica.
When the proto-Europe collided with North America, the collision folded coastal sediments that had been accumulating since the Cambrian off the east coast of North America and the west coast of Europe. This event is the Caledonian orogeny, a spate of mountain building that stretched from New York State through conjoined Europe and Greenland to Norway. At the end of the Silurian, sea levels dropped again, leaving telltale basins of evaporites in a basin extending from Michigan to West Virginia, and the new mountain ranges were rapidly eroded. The Teays River, flowing into the shallow mid-continental sea, eroded Ordovician strata, leaving traces in the Silurian strata of northern Ohio and Indiana.
The vast ocean of Panthalassa covered most of the northern hemisphere. Other minor oceans include two phases of the Tethys— the Proto-Tethys and Paleo-Tethys— the Rheic Ocean, a seaway of the Iapetus Ocean (now in between Avalonia and Laurentia), and the newly formed Ural Ocean.
Climate and sea level
The blue graph shows the apparent percentage (not the absolute number) of marine animal genera becoming extinct during any given time interval. It does not represent all marine species, just those that are readily fossilized.
The Silurian period enjoyed relatively stable and warm temperatures, in contrast with the extreme glaciations of the Ordovician before it, and the extreme heat of the ensuing Devonian. Sea levels rose from their Hirnantian low throughout the first half of the Silurian; they subsequently fell throughout the rest of the period, although smaller scale patterns are superimposed on this general trend; fifteen high-stands can be identified, and the highest Silurian sea level was probably around 140 m higher than the lowest level reached.
During this period, the Earth entered a long, warm greenhouse phase, and warm shallow seas covered much of the equatorial land masses. Early in the Silurian, glaciers retreated back into the South Pole until they almost disappeared in the middle of Silurian. The period witnessed a relative stabilization of the Earth’s general climate, ending the previous pattern of erratic climatic fluctuations. Layers of broken shells (called coquina) provide strong evidence of a climate dominated by violent storms generated then as now by warm sea surfaces. Later in the Silurian, the climate cooled slightly, but in the Silurian-Devonian boundary, the climate became warmer.
Perturbations
The climate and carbon cycle appears to be rather unsettled during the Silurian, which has a higher concentration of isotopic excursions than any other period. The Ireviken event, Mulde event and Lau event each represent isotopic excursions following a minor mass extinction and associated with rapid sea-level change, in addition to the larger extinction at the end of the Silurian. Each one leaves a similar signature in the geological record, both geochemically and biologically; pelagic (free-swimming) organisms were particularly hard hit, as were brachiopods, corals and trilobites, and extinctions rarely occur in a rapid series of fast bursts.
The Silurian was the first period to see macrofossils of extensive terrestrial biota, in the form of moss forests along lakes and streams. However, the land fauna did not have a major impact on the Earth until it diversified in the Devonian.
The first fossil records of vascular plants, that is, land plants with tissues that carry food, appeared in the second half of the Silurian period. The earliest known representatives of this group are Cooksonia (mostly from the northern hemisphere) and Baragwanathia (from Australia). Most of the sediments containing Cooksonia are marine in nature. Preferred habitats were likely along rivers and streams. Baragwanathia, appears to be almost as old dating to the Early Ludlow (420 million years) and has branching stems and needle-like leaves of 10-20 cm. The plant shows a high degree of development in relation to its age. As mentioned, fossils of this plant are only found in Australia.
The much-branched Psilophyton was a primitive Silurian land plant with xylem and phloem but no differentiation in root, stem or leaf. It reproduced by spores, had stomata on every surface, and probably photosynthesized in every tissue exposed to light. Rhyniophyta and primitive lycopods were other land plants that first appear during this period. Neither mosses nor the earliest vascular plants had deep roots. Silurian rocks often have a brownish tint, possibly a result of extensive erosion of the early soils.
The first bony fish, the Osteichthyes, appeared, represented by the Acanthodians covered with bony scales; fish reached considerable diversity and developed movable jaws, adapted from the supports of the front two or three gill arches. A diverse fauna of Eurypterids (sea scorpions)—some of them several meters in length—prowled the shallow Silurian seas of North America; many of their fossils have been found in New York state. Leeches also made their appearance during the Silurian Period. Brachiopods, bryozoa, molluscs, hederelloids, tentaculitoids, crinoids and trilobites were abundant and diverse.
Reef abundance was patchy; sometimes fossils are frequent but at other points are virtually absent from the rock record.
The earliest known terrestrial animals appear during the Mid Silurian, including the millipede Pneumodesmus. Some evidence also suggests the presence of predatory trigonotarbid arachnoids and myriapods in Late Silurian facies. Predatory invertebrates would indicate that simple food webs were in place that included non-predatory prey animals. Extrapolating back from Early Devonian biota, Andrew Jeram et al. in 1990 suggested a food web based on as yet undiscovered detritivores and grazers on micro-organisms.
Note : The above story is based on materials provided by Wikipedia
