Daily Science Dose

Did you know that the present time is already considered one of the great mass extinctions? Humans seem to be the major culprit in this, the Holocene extinction event, but scientists have recently began surmising that a similar extinction 251 million years ago was caused by the same thing. But with no humans around 251 million years ago, what is it that I am talking about — yep, carbon dioxide.

The Christian Science Monitor published an article this last week detailing the current hypotheses of a team of researchers and scientists from multiple disciplines.

Now scientists are rethinking another of earth’s great die-offs. The end-Permian extinction 251 million years ago was the worst of earth’s five mass extinctions. Ninety percent of all marine life and 70 percent of terrestrial life disappeared. It took five million years, perhaps more, for the biosphere to recover.

But while the die-off was uniquely devastating, evidence of a single cataclysmic event, like an asteroid strike, hasn’t been found in the geological record. Scientists now suspect that “the mother of all mass extinctions” was of Earth’s own making. And the more they learn about it, the more parallels they see to today’s world: A bout of greenhouse-gas-induced global warming, much like today’s, set off a chain of events that culminated in oxygen-depleted oceans exhaling poison gas.

It seems that increased volcanic activity started burning through coal beds, releasing enormous amounts of carbon dioxide — something we humans are doing, we are like little volcanoes, I guess. The Earth’s population at the time was already stressing the system, and when the extra CO2 entered the atmosphere, it lead to warmer seas (sounds familiar). The warmer seas lead to increased weathering and erosion, which washed nutrients into the oceans, thus leading to algae blooms (again, familiar). When the algae dies, the decomposition process requires oxygen, effectively starving the water of oxygen. When water does not have enough oxygen, many organisms cannot live in that water, except for anaerobic organisms that breathe in sulfates and give off hydrogen sulfide as exhalation. Hydrogen sulfide is poisonous to us oxygen-loving organisms.

And the lessons for today? At the Permian boundary, “you’re in a state of gradual warming, then as you approach that boundary, the warming in­­creases dramatically,” says Jeff Kiehl, a senior scientist at the Na­­­tion­­­al Center for Atmospheric Re­­search in Boulder, Colo. “It wasn’t a linear warming.” Says Professor Kump: “This shows us what could happen if we push the system too hard…. We don’t know where the intermediate thresholds are.”

We’re still some way from the atmospheric CO2 levels hypothesized at the end-Permian extinction – which were perhaps 10 times preindustrial levels, or 2,800 ppm. Yet, according the Intergovernmental Panel on Climate Change, if trends continue we’re still approaching 1,000 ppm of CO2 by 2100. That’s not Permian-extinction levels, but it would be the highest CO2 concentration in 80 million years, and a level at which both ocean anoxia and lesser extinctions have occurred.

This theory on what lead to the “great dying” at the transition between the Permian and Triassic periods (the extinction event is called the Permian-Triassic extinction event, appropriately enough) has been bouncing around for a while now, once scientists started questioning the evidence of the Killer Asteroid that killed off the dinosaurs. It seems that despite the asteroid’s impact and subsequent devastation, many big dinosaurs stuck around for quite some time afterward. When the asteroid impact theory gained popularity, some scientists felt that all of our many mass extinctions throughout Earth’s history were caused by otherworldly impacts, but not all the evidence added up.

Until fossil records started showing evidence of little sulfide-emitting organisms, and then scientists started looking at the Permian-Triassic more carefully.

From a Scientific American article from 2006:

But the biomarkers in the oceanic sediments from the latest part of the Permian, and from the latest Triassic rocks as well, yielded chemical evidence of an ocean-wide bloom of the H2S-consuming bacteria. Because these microbes can live only in an oxygen-free environment but need sunlight for their photosynthesis, their presence in strata representing shallow marine settings is itself a marker indicating that even the surface of the oceans at the end of the Permian was without oxygen but was enriched in H2S.

Also, the P-Tr event is marked by volcanic activity in Siberia, of all places, and only a couple of months ago, scientists discovered that large amounts of methane are leaking from the Siberia Seabed. Hmm, methane is a greenhouse gas that has 20 times the power to trap heat that carbon dioxide does, and if that “leak” continues, well, estimates that 50 percent of all species will go extinct in the next century may not be too far off the mark.

extinction, mass, permian, triassic, dinosaurs, humans, mammals, volcanic activity, volcanoes, asteroid, impact, Siberia, methane, carbon dioxide, population stress, warming seas, sulfides, oxygen, algae bloom, anaerobic, greenhouse gas, global warming