Paleo research shows that the five true mass extinction events in Earth´s history can all be linked to large climatic shifts, mostly as a consequence of rare geological events, like the breakup or collision of continents.
The last three mass extinctions (250-65 mya)
In the case of number three of five, the largest such event, the Permian-Triassic Extinction or The Great Dying some 250 million years ago, this led to enormous CO2 emissions, from both fossil sources and the biosphere.
About 50 million years later another carbon disaster struck Earth, as the release of an estimated 16,000 gigatonnes of methane from ocean clathrates [yes, apparently it can happen] led to the Triassic-Jurassic mass extinction, the fourth large-scale biodiversity die-off.
Only the Cretaceous-Tertiary – some 65 million years ago and thus far the last mass extinction, which wiped out a large portion of Earth’s biodiversity including the dinosaurs and ammonites [but left more than us mammals surviving underground], was probably caused by something hard and heavy from outer space [although tracing that famed asteroid proves difficult].
A good climate is stable enough
Ever since Earth has returned to millions of years of relative peace and quiet, which means evolution has had the time to repair the damage, overcompensating a bit here and there by adding some fun new designs.
Relative means Earth’s climate has been stable enough over these last 65 million years not to challenge life itself, by endangering the survival of entire taxonomic orders. But of course there have been many different climatic variations since, ranging from the ice ages of the Pleistocene to the warm Eocene, which was preluded by the Paleocene-Eocene Thermal Maximum (PETM), a methane-induced temperature spike some 55 million years ago that did kill quite a significant portion of Earth’s biodiversity, especially in the oceans.
Smaller climate change, smaller extinctions
Now a new study indicates that this probably goes for the other smaller climatic fluctuations of the Cenozoic [the current geological era, which started after the C-T extinction 65 million years ago] as well – as a team of researchers from Brown University in the US and the Spanish universities of Málaga and Valencia has linked the disappearance of groups of dominant North-American mammals over the last 65 million years to 6 different climatic change events, indeed including the PETM.
In their PNAS publication of two days ago they write that four of the events show a strong correlation to the occurrence of climatic changes, while the two others were a consequence of the influx of new mammal species from other continents – combined again with a climate change correlation.
Closing in on modern times
Other recent research shows that also in the decline of the ice age megafauna the detrimental effects of climate change on survival chances were exacerbated by competition with other mammals, one in particular.
And as that one mammal is still freely walking around in the billions the current mammal extinction rate is 160,000 times higher than it was on average over these last 65 million years ago, we learned from a Nature study in March this year.
That indeed means we have something to think about at the end of the year, as [yet another 2011 publication tells us] we are on the eve of the Sixth Mass Extinction, using that well-tested climate mechanism to write planetary history.
© Rolf Schuttenhelm | www.bitsofscience.org