Life finds a way

I've written here before about the Permian-Triassic Extinction, sometimes nicknamed "the Great Dying."  It occurred 251.9 million years ago, and like the Cretaceous Extinction 186 million years later -- the one that knocked out the non-avian dinosaurs -- it happened suddenly, destroying ecosystems worldwide that had been thriving prior to the event.

The cause of this cataclysm is still a matter of some debate.  Hypotheses include:

• The formation of the Siberian Traps, an unimaginably huge lava flow covering most of eastern Siberia. (Its volume is estimated at four hundred million cubic kilometers.)  The eruption would have burned everything in its wake, ripping through the vast Carboniferous coal and limestone beds, pumping tons of carbon dioxide into the atmosphere.  It would also have released huge amounts of sulfur dioxide -- not only a poison, but one of the most powerful greenhouse gases.  The result; massive global warming, oceanic acidifiction, and a catastrophic change in ecosystems worldwide.
• The lockup of Pangaea.  The collision of smaller continents to form a supercontinent has a number of effects -- the eradication of coastline along the colliding margin, ecological changes from shifting ocean currents, and collapse of mid-ocean ridges (resulting in a huge drop in sea level) among them.
• A "methane burp."  This sounds innocuous, but really, really isn't.  There's a tremendous amount of methane locked up in the form of clathrates -- a network of water ice with methane trapped inside.  These "frozen methane hydrates" coat the entire deep ocean floor.  The stuff is stable under cold temperatures and high pressures, but if something disturbs them, they begin to come apart, releasing bubbles of methane gas.  The bubbles expand as they rise, displacing more and more water, and when they hit the surface it causes a tsunami, not to mention releasing tons of methane into the atmosphere, which is not only toxic, it's also a greenhouse gas.
• Bombardment by swarms of comets and/or meteorites.  The problem with confirming this hypothesis is that any geological evidence of meteorite collisions would be long since eroded away.  If the object(s) that impacted the Earth were metallic meteorites, it's possible that you could use the same technique Luis Alvarez pioneered to explain the Cretaceous Extinction, which wiped out most of the dinosaurs -- enrichment of a layer of sediment by dust that's high in metallic elements not found in large quantities elsewhere.  But if it was a comet (mostly ice) or a rocky meteorite, we might not see much in the way of evidence of the event.

Current expert opinion is that the first one is strongly implicated as the prime cause, but the others may have played a role as well.

In any case, the end result was the extinction of an estimated 95% of marine life and 85% of terrestrial life.  Several groups that had been dominant for millions of years -- trilobites, eurypterids, blastoids, and the orthid and productid brachiopods, for example -- were wiped out completely.

It's hard to fathom what this would be like (although we'd damn well better try; there are estimates of the current, largely anthropogenic, extinction rate that place it in the same range as the Permian-Triassic).  Overall, it seems like ninety percent of the world's species died.  At the same rates today, we'd be left with a grand total of two hundred species of birds in all of North America -- and only forty different kinds of mammals.  

The reason this rather dismal topic comes up is some new research that actually provides a glimmer of hope; a find by paleontologists in China suggesting that after this cataclysm, life rebounded amazingly fast -- resulting in thriving and diverse ecosystems in as little as a million years.

Artists' reconstruction of the Guiyang biota [Image courtesy of artists Dinghua Yang and Haijun Song]

The most amazing thing about this is that at that point, the situation was still, in a word, lousy.  The average sea surface temperature at the equator is estimated at around 35 C (95 F).  The pH was still way down -- how far down isn't known, but certainly enough to inhibit calcium carbonate production by mollusks and corals.  The carbon dioxide levels were still sky-high.  But astonishingly, the organisms that made it through the bottleneck managed to adapt even to these hostile conditions.  Even in the (very) early Triassic Period, life found a way to adapt.

I hesitate to draw too much cheer from all this, however.  The fact that the species who survived the Great Dying eventually did okay is little consolation to the tens of thousands of species that went extinct.  Even if what we're now doing -- rampant fossil fuel use, pollution, and deforestation -- won't wipe out every last living thing on Earth, the results could still be beyond catastrophic.  And while it's "geologically rapid," "recovery in a million or so years" won't help our children and grandchildren.

It's time we extend "learn from the past rather than ignoring it" to prehistoric events, not just historical ones.

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