The Great Dying

2007-08-29

in Daily updates, Science, The environment

Elephant statue, National Gallery of Canada

251.4 million years ago, the earth experienced the most severe extinction event ever recorded. The Permian-Triassic (P-Tr) extinction event (informally referred to as the Great Dying) involved the loss of 90% of all extant species. This included about 96% of all marine species and 70% of terrestrial vertebrate species.

There are a number of theories about what caused the event:

  1. A comet or meteor impact
  2. Massive volcanic activity
  3. Continental evolution
  4. A supernova destroying the ozone layer
  5. Methane clathrate release

Some combination of such factors may well be responsible. Regardless of the initial cause, one of the defining elements of the P-Tr event was a high degree of global warming. Mean global temperatures increased by about 6°C, with much higher increases at the poles. This period also involved the large-scale failure of ocean circulation, leaving nutrients concentrated at the ocean bottom and an acute lack of oxygen in the sea. The latter was the product both of decreased circulation and the large-scale die off of the kind of phytoplankton species that now produce about 90% of the planet’s oxygen.

The study of such historical occurrences is useful, largely because it helps to improve our appreciation for how climatic and biological systems respond to extreme shifts. Just as the re-emergence of life after a forest fire and a clearcut may have some common properties, perhaps the patterns of decline and reformation after the P-Tr event can offer us some insight into macro level processes of ecological succession after traumatic climatic events.

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{ 7 comments… read them below or add one }

Litty August 29, 2007 at 8:37 pm

Something like that will sure make seperating my paper from plastics seem like a big waste of time.

Neal August 30, 2007 at 12:59 am

Interestingly, the only large terrestrial vertebrate to survive the End-Permian was Lystrosaurus, a stout quadruped which looked like a reptilian pig, complete with tusks and a shovel like snout.

This leads me to conclude that should we warm the earth sufficiently to bring about such a catastrophe, that the only survivors will be humans mutated into hideous pig-reptiles by the last of the biotech wars. They will scratch out a meager subsistence using their tusks and acute sense of smell to forage for the thorium fortified tubers of the mutato, a hybrid staple crop designed to survive the nuclear winter brought about by a nuclear exchange fought between the leaders of the Rangoon Pact and the Holy McGoogle Empire.

Milan August 30, 2007 at 8:17 am

That Lystrosaurus is one handsome beast.

Its Pokemon-like appearance will also create affection for it among children.

. October 8, 2008 at 4:09 pm

Although the atmospheres and climates of Venus and Earth differ very greatly today, it is generally believed that the two planets started out in a rather similar state, but subsequently evolved along divergent paths. Venus succumbed early to a “runaway water vapor greenhouse,” in which the increased water vapor content arising from increased temperature reached an end state with much of the ocean evaporated into the atmosphere. Once this happens, it is easy for the water vapor to decompose in the upper atmosphere, whereafter the light hydrogen escapes and oxygen either escapes or reacts with rocks. One hypothesis is that the weak magnetic field at Venus, which otherwise would protect the planet from the solar wind, is one reason for why the oxygen and hydrogen escaped faster into space. Once water is lost, the reaction that turns carbon dioxide into limestone can no longer take place, so CO2 outgassing from volcanoes accumulates in the atmosphere instead of staying bound up in the rocks. The end state of this process is the current atmosphere of Venus, with essentially no water in the atmosphere and essentially the planet’s whole inventory of carbon in the form of atmospheric CO2.

. October 14, 2008 at 3:28 pm

But this has always been one of Weaver’s strengths. Without ever dumbing the issue down, he keeps it as simple and understandable as he can.

He agrees the crux of his book comes down to a single alarming sentence on page 28: “People have simply no idea how serious this issue is.”

It’s so serious, he said, that unless we reach a point where we stop emitting greenhouse gases entirely, 80 per cent of the world’s species will become extinct, and human civilization as we know it will be destroyed, by the end of this century.

. April 7, 2010 at 11:59 am

“Crucially, the period of plummeting coincides with a phenomenon called the late Triassic fern spike. This marks precisely—to within a few thousand years—the point of mass extinction on the land. What is believed to have happened is that something killed all the forests and with them the animals that depended on them. Freed from the competition for light (because the shade from the trees had gone), ferns flourished (their spores are ubiquitous in the rocks). Previous work has suggested that the oceans also became acidic at this time. Shelled creatures, whose calcium-carbonate-rich armour tends to dissolve in acid, suddenly became rare.

Put it all together and the probable course of events was this. The initial volcanism as North America split from Europe released carbon dioxide from deep inside the Earth. That produced a greenhouse effect which, in turn, melted seabed structures known as methane clathrates, which trap that gas in ice. This caused a massive release of 12C-rich methane into the atmosphere, explaining the initial drop in 13C concentrations. The methane, being a much more potent greenhouse gas than carbon dioxide, exacerbated things, while the carbon dioxide acidified the oceans, killing most of the animal shellmakers and fertilising the photosynthesis of planktonic plants. The subsequent plankton bloom sucked up the 12C and the isotope ratio veered off in the opposite direction.

The greenhouse warming and the acid rain also did for the forests and many of the reptiles. Only once things had settled down could the survivors regroup. New species of trees took over. The forests grew back. And a bunch of hitherto not-so-terrible lizards began their long march.”

. January 26, 2011 at 6:11 pm

Toxic Ash Clouds Might Be Culprit in Biggest Mass Extinction
by Sid Perkins on 23 January 2011, 1:00 PM

Tiny particles embedded in ancient Canadian rocks have provided new clues about what might have triggered Earth’s deadliest mass extinction. The ultimate cause, researchers say, might be globe-smothering clouds of toxic ash similar to that spewed by modern-day coal-fired power plants.

The die-off, which occurred worldwide about 250 million years ago at the end of the Permian period, was even more extensive than the one that wiped out the dinosaurs. More than 90% of marine species went extinct, and land-based ecosystems suffered almost as much. Scientists have long debated the reasons. Favorite hypotheses include an asteroid impact, massive volcanic eruptions in Siberia, and toxic oceans. Geochemist Stephen Grasby of the Geological Survey of Canada in Calgary and colleagues report online today in Nature Geoscience a new twist on the volcano notion.

Rocks that now make up the northernmost islands of the Canadian Arctic formed millions of years ago as seafloor sediments off the northwestern coast of a supercontinent called Pangaea. When Grasby and his team analyzed rocks from just before the Permian mass extinction, they noticed unusual microscopic particles. Besides the usual miniscule clumps of organic matter, they also found tiny bubble-filled particles called cenospheres. These frothy little blobs form only when molten coal spews into the atmosphere, the researchers say. Today, the fly ash produced by coal-fired power plants brims with cenospheres, but they are largely trapped by pollution-control equipment before they escape the smokestack. Millions of years ago, they must have been created when massive amounts of molten rock—more than 1 trillion metric tons—erupted through overlying coal deposits in Siberia to form lava deposits known as the Siberian Traps.

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