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Ordovician mass extinction
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 Scientists show how some species survive rapid climate change - and others don't

Why some species died out and others didnt during the Earths second largest mass extinction has been revealed in a new study.
It coincided with a short but intense ice age and California Institute of Technology (Caltech) researchers believe that species died out if large portions of their habitat were lost to ice sheets and falling sea levels.
Those that had always been confined to warm tropical waters were also most likely to go extinct as a result of the rapid climate change.
The so-called Late Ordovician mass extinction occurred about 450 million years ago.

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Ordovician mass extinction event
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A new study has suggested that a brilliant burst of gamma rays may have caused a mass extinction event on Earth 440 million years ago, and a similar celestial catastrophe could happen again in the future.
Most gamma-ray bursts are thought to be streams of high-energy radiation produced when the core of a very massive star collapses.
According to a report in National Geographic News, the new computer model shows that a gamma-ray burst aimed at Earth could deplete the ozone layer, cause acid rain, and initiate a round of global cooling from as far as 6,500 light-years away.
Such a disaster may have been responsible for the mass die-off of 70 percent of the marine creatures that thrived during the Ordovician period (488 to 443 million years ago), suggests study leader Brian Thomas, an astrophysicist at Washburn University in Kansas.

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RE: Toyonian mass extinction event
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Title: Late Ordovician geographic patterns of extinction compared with simulations of astrophysical ionising radiation damage
Authors: Adrian L. Melott (U. Kansas), Brian C. Thomas (Washburn U.)
(Version v2)

Based on the intensity and rates of various kinds of intense ionising radiation events such as supernovae and gamma-ray bursts, it is likely that the Earth has been subjected to one or more events of potential mass extinction level intensity during the Phanerozoic. These induce changes in atmospheric chemistry so that the level of Solar ultraviolet-B radiation reaching surface and near-surface waters may be approximately doubled for up to one decade. This UVB level is known from experiment to be more than enough to kill off many kinds of organisms, particularly phytoplankton. It could easily induce a crash of the photosynthetic-based food chain in the oceans. Certain regularities in the latitudinal distribution of damage are apparent in computational simulations of the atmospheric changes. It was previously proposed that the late Ordovician extinction is a plausible candidate for a contribution from an ionising radiation event, based on environmental selectivity in trilobites. In order to test a null hypothesis based on this proposal, we confront latitudinal differential extinction rates predicted from the simulations with data from a published analysis of latitudinal gradients in the Ordovician extinction. We find that the pattern of damage predicted from our simulations is consistent with the data assuming a burst approximately over the South Pole. We predict that any land mass (such as part of north China) which then lay about 20 degrees or more north of the equator should be a refugium from the UVB effects, and show a different pattern of extinction in the first strike of the end-Ordovician extinction, if it were induced by such a radiation event.

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Posts: 131433
Date:
Late Ordovician mass extinction event
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Title: Late Ordovician geographic patterns of extinction compared with simulations of astrophysical ionising radiation damage
Authors: Adrian L. Melott (U. Kansas), Brian C. Thomas (Washburn U.)

Based on the intensity and rates of various kinds of intense ionising radiation events such as supernovae and gamma-ray bursts, it is likely that the Earth has been subjected to one or more events of potential mass extinction level intensity during the Phanerozoic. These induce changes in atmospheric chemistry so that the level of Solar ultraviolet-B radiation reaching surface and near-surface waters may be approximately doubled for up to one decade. This UVB level is known from experiment to be more than enough to kill off many kinds of organisms, particularly phytoplankton. It could easily induce a crash of the photosynthetic-based food chain in the oceans. Certain regularities in the latitudinal distribution of damage are apparent in computational simulations of the atmospheric changes. It was previously proposed that the late Ordovician extinction is a candidate for a contribution from an ionising radiation event, based on environmental selectivity in trilobites. We confront this hypothesis with data from a published analysis of latitudinal gradients in the Ordovician extinction. We find that the pattern of damage predicted from our simulations is consistent with the data assuming a burst approximately over the South Pole. However, the patterns are not sufficiently selective as to be said to provide strong evidence for the ionising radiation hypothesis. We predict that any land mass (such as part of north China) which then lay substantially north of the equator should be a refugium from the UVB effects, and show a different pattern of extinction in the first strike of the end-Ordovician extinction, if it were induced by such a radiation event.

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Late Devonian Mass Extinctions
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Scientists recognise a number of mass extinctions (extinction events that far exceed background extinction rates and are not taxonomically restricted). Five of these were particularly severe: the terminal Ordovician, Late Devonian, terminal Permian, terminal Triassic, and terminal Cretaceous. There is general agreement that four of these "Big Five" events were relatively restricted in duration (i.e., <1-5 million years). The timing and duration of the Late Devonian mass extinction(s), however, are subject to considerable debate and a variety of interpretations.

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Trilobites reveal pattern of early animal evolution on Earth
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The abundant diversity of characteristics within species likely helped fuel the proliferation and evolution of an odd-looking creature that emerged from an unprecedented explosion of life on Earth more than 500 million years ago. University of Chicago palaeontologist Mark Webster reports this finding in the current issue of the journal Science.

From an evolutionary perspective, the more variable a species is, the more raw material natural selection has to operate on - Mark Webster , an Assistant Professor in Geophysical Sciences at Chicago.

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RE: Toyonian mass extinction event
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A depiction of the different orders of trilobites, when they existed, and their relationships to each other. Notice how most trilobites went extinct at the late Devonian, and only Proetida went on into the Carboniferous and Permian


Expand (315kb, 1024 x 741)
Credit  Goniagnostus


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Trilobite
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It's new, but it's old. "Trilobite Treasures: Arthropods of the Ancient is a walk on the wild side to prehistoric times. This temporary exhibit at the Family Museum in Bettendorf, Iowa, offers a chance to view fossils more than 320 million years old. Of particular interest are the Trilobites from the Kchodl collection, more than 200 prehistoric specimens and artefacts from all over the world.
Trilobites are hard-shelled, segmented creatures that were crawling in the Earth's ancient seas by the thousands, but became extinct well before the dinosaurs roamed. They fossilised easily and so have left an extensive record of their existence.
In addition to the fossils, the exhibit, which concludes Aug. 5, features original artwork, Trilobite jewellery and other artefacts. Included in the display will be information on Trilobite discovery, history, research and preservation.

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Toyonian mass extinction event
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Half-a-billion years ago, as an explosion of life was starting to produce diverse new forms, the Antrim Plateau Volcanics of northern Australia began spewing massive amounts of lava.

Before it was over, lava floods had buried almost a fifth of Australia's area today.
The newly identified Kalkarindji Continental Flood Basalt Province covered at least 644,000 square kilometres with more than 193,000 cubic kilometres of lava - to an average depth of 500 metres.
Centred several hundred kilometres south of where Darwin is now, the eruption might also have triggered a mass extinction of Early Cambrian reef-builders (mainly Archeocyatha) and reef-dwellers (trilobites and other creatures).

"You can imagine the gasses pouring into the atmosphere, a lot of greenhouses gasses" - Dr Linda Glass, geochemist for the Northern Territory Geological Survey.

Dr Glass discovered the extent of the eruption after spending five months driving around northern Australia collecting rocks for investigation. The lava floods stretch from Queensland in the East to the Kimberley area in Western Australia and underlies a large part of the Palaeozoic rocks of the Daly River, Wiso and Georgina basins.

"It was a very large igneous event. Nothing is comparable with it today. It makes Hawaii's look like a blip" - Dr Linda Glass.

Dr Glass found evidence of 16 lava flows, piled on top of each another, with one measuring 200 metres thick.
Rocks found as far away as south-western Western Australia and Antarctica might have been part of those lava floods. These are the oldest such lava formations dated using Argon-40/Argon-39 techniques.

Another important aspect of the massive eruption is that it took place shortly after the explosion of life forms during the Lower Cambrian Period about 535 million years ago. The half-billion-year-old eruption might be the culprit in the first mass animal extinction event in the history of life.

"It certainly would have had global effects. A proliferation of life took place in the Cambrian period of geology, 500 to 550 million years ago. We do know there were extinction events 500 to 515 million years ago which wiped out a number of species" - Dr David Phillips.

The triggered may have been shifting plate tectonics, which were rotating Australia 90 degrees anti-clockwise at the time.

Adapted from Source

-- Edited by Blobrana at 15:03, 2006-06-30

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