Something about heat is intrinsically bad for life. Shown is the state of our planet from 252-247 million years ago, following the end-Permian mass extinction. The 40+C Triassic Dead Zone could not be conquered by 5 million years of evolution. Image credit: Yadong Sun, University of Leeds.
The Permian-Triassic Mass Extinction nearly killed life on Earth in its entirety. In the oceans for instance 97 percent of all species became extinct. Planet-wide, an estimated 83 percent of genera and 57 percent of families were lost. Therefore the P-T Extinction is also referred to as the ‘mother of mass extinctions’ or The Great Dying.
Science sort of knows why life got into such big trouble at the end-Permian. It was a cascade that started with geological disaster in the form of mass volcanology, which triggered Pangaea-scale forest fires and enormous carbon release, microbial plagues, mercury poisoning, ocean anoxia and ocean acidification – all of which contributed to ecosystem collapses, mercilessly cutting through interspecies dependency links.
But that is the story of the end-Permian. The other side of the boundary – the Triassic – has a different story to tell.
The Triassic ‘Dead Zone Planet’
There is of course a big difference between the extinction of all of life, and that of ‘nearly all.’ In fact evolution could count itself lucky that [after already billions of years of continuous hard labour, let’s credit her!] the end-Permian started off with living representatives for all of Biology’s 6 Kingdoms set in the starting blocks, ready for round two of Project Life on Earth.
But then the fossil record showed Earth remained a dead planet for a very long time. Some say 5 million years, others say ten. Well now Gaia, we know you lost a lot of dear ones, but isn’t that a bit overly dramatic?
No, we think it makes good sense, say researchers from China University of Geosciences, the University of Leeds, Universität Erlangen-Nürnberg and the University of Graz in her defense.
Apparently there is a goldilocks’ argument in temperature as well – and there is a certain average temperature level in Earth’s climate system that life finds intrinsically too hot, that is, ‘we’ve thought of baobabs, savanna grass and shrubs, cacti, sand-digging ants and beetles, we’ve thought of lizards, snakes – heck, even of camels – and whatever reptiles and other tropical ectotherms one can imagine’ – but this is a warming none of us like.
In a new Science publication the above-mentioned researchers state “that the end-Permian mass extinction coincided with a rapid temperature rise to exceptionally high values in the Early Triassic that were inimical to life in equatorial latitudes and suppressed ecosystem recovery.”
“This was manifested in the loss of calcareous algae, the near-absence of fish in equatorial Tethys, and the dominance of small taxa of invertebrates during the thermal maxima. High temperatures drove most Early Triassic plants and animals out of equatorial terrestrial ecosystems and probably were a major cause of the end-Smithian crisis.”
All right. So what to imagine of these ‘Lethally hot temperatures during the early Triassic greenhouse’ – as their article is titled? Could you boil an egg in that Tethys Ocean?
No, you could not. In fact, you could swim in it [lovely sun, no risks of sharks from here to any horizon. But don’t go for hours on end, you’d start to feel a bit feverish.]
The heat that is lethally hot
The large-scale carbon cycle disturbances of the end-Permian left the Triassic with an elevated greenhouse state and temperatures that were in tropical[!] surface waters on average some 40 degrees Celsius around the Tethys coasts – ten degrees higher than previous research had suggested, and on the lethal threshold, the Science publishers say.
Over equatorial land masses temperatures would be around 50 to 60 degrees. Indeed, imagine your last summer holidays in the Sahara. The Triassic tropics were hot, exactly by today’s standards of that word.
Of course, including seasonal extremes, we couldn’t stand the Triassic tropics. But humans would not be alone. For a multi-million years’ time period, before Triassic temperature gradually sank, evolution could not think of heat-adapted ecosystems – and Earth in fact carried a very wide ‘dead zone’ around its waist.
Big lesson to learn (how we see it): it is not just the speed of climate change [through impaired adaptability] that causes biodiversity damage – there is also something about heat that is intrinsically bad for life.
© Rolf Schuttenhelm | www.bitsofscience.org