Extinctions in the CambrianThe geologic record shows many instances where large numbers of species h

Extinctions in the CambrianThe geologic record shows many instances where large numbers of species have gone extinct. The five biggest tend to be lumped together as “mass extinctions”. At those times, so many things changed that early geologists created new geologic eras with the extinctions at the boundaries, like the Permian-Triassic boundary, at those times.Along with the “big 5”, there are other extinctions that were either smaller or didn’t leave strong geologic traces but still had profound impacts on the history of life. One of these occurred during the Cambrian period, 510 million years ago.The Cambrian was a key time in the development of life; it was shortly after organisms began producing hard shells and so many of the body formats we see today began developing in the Cambrian. This extinction happened just over 30 million years after the Cambrian began, so it had major impacts on the type of body-formats that survive to this day. By some estimates, around 50% of marine species died during that extinction; much smaller than the end-Permian extinction, but still a major calamity.Trying to figure out the cause of an event so long ago is really tough. Many of the rocks have eroded leaving only pieces of evidence, but new research published in the journal Geology makes a circumstantial case that the cause was the eruption of these rocks; lavas that poured out in what is today the Kimberley region of Western Australia.From rocks in other parts of the world, the extinction has been dated to have happened at 510 million years ago. Scientists led by the University of Western Australia sampled these lavas, dated them, and found the ages of the lavas were identical to the age of the extinction.Large outpourings of lava have been implicated in other extinctions. The most obvious is the eruptions of the Siberian Traps, 251 million years ago, that lines up with the end-Permian mass extinction. In that case though, the lavas interacted with large coal deposits, potentially causing the release of caustic gases like sulfuric acid or carbon dioxide to the atmosphere that could have poisoned life. In this case, how the extinction happened is much less clear.There is no evidence of these eruptions hitting coal seams; in fact, there weren’t even plants living on land at the time. The lavas do carry gases and elements that could impact the chemistry of the oceans and cause dramatic climate changes, but how that would translate into the deaths of large numbers of species isn’t clear.The connection between mass extinctions and large igneous provinces isn’t straightforward. Siberia might be the best case, but even with that eruption there were other changes happening in the ocean that could have contributed to the extinction as well. On the other hand, there are major eruptions, like the one that formed the enormous Ontong-Java plateau, which happened without any major extinction. Seeing another extinction tentatively connected to a large igneous province is intriguing, but these tentative connections leave me skeptical until I understand how it happened.-JBBImage credit: Lena Evins (author on the study)http://phys.org/news/2014-05-kimberley-mass-extinction-complex-life.htmlOriginal paper (subscription):http://www.crossref.org/iPage?doi=10.1130%2FG35434.1 -- source link

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