|'Permian-Triassic Boundary, notorious for being the most devastating extinction event in the planet's history (95% of life wiped out in a geological blink). It is located at Austinmer, a coastal suburb between Sydney & Wollongong, Australia.' Source|
About 252 million years ago the Permian–Triassic extinction event killed off the majority of Earth's species on land and sea.
At this time most of the world's landmasses were gathered into a supercontinent (not the first) called Pangaea:
It's thought that the cause of the 'Great Dying' was volcanic activity in what is now Siberia (at the top of the above picture.) Great volumes of 'greenhouse gases' were released into the atmosphere.
As the atmosphere warmed up - some say to well over 100°F across Pangaea - so did the oceans. Warm water can hold less oxygen than cold, so oxygen levels dropped. Marine species in cooler areas north and south, which were used to oxygen-rich water, asphyxiated; tropical species, which had already adapted to cope with less-oxygenated water, were more likely to survive.
As the oceans became less hospitable amphibians, which had dominated the Permian period, were displaced by
'reptiles—notably the archosaurs ("ruling lizards") and therapsids ("mammal-like reptiles"). For reasons that are still unclear, the archosaurs held the evolutionary edge, muscling out their "mammal-like" cousins and evolving by the middle Triassic into the first true dinosaurs like Eoraptor and Herrerasaurus.'
Ironically, an earlier mass extinction - 150 million years before the Permian-Triassic event - was caused by falling CO2 levels as a result of the spread of plant life:
'In the Devonian period the world was experiencing super greenhouse climate conditions. This means that it was very warm, there probably were no ice caps, there was a lot of carbon dioxide in the atmosphere (with estimates of 4,000 parts per million).
'"As plant communities expanded onto land to form the first forests, they depleted the carbon dioxide (CO2) that was in the atmosphere," Waters said. "CO2 levels dropped to 400 ppm toward the end of the Devonian. It got colder. There were glaciation events and the rapid change in the climate caused severe extinction in the tropics and the existing coral reefs became extinct." By comparison, the world's current CO2 level is very close to 400 ppm.'
The fall in CO2 levels is thought to have stimulated the development of woody plants and eventually trees. According to this video (see from 3:09), plants that breathe in CO2 through holes called 'stomata' gradually had to hold them open for longer to get enough of the gas; this also meant they lost more water through evaporation via the same holes. Woody structures were better at holding and transporting water though the body of the plants.
A lesson for us is that we need not worry about 'saving the planet' - life adapts. The question is, can we save ourselves?
P.S. This site says that an end-Permian-type ocean warming and marine extinction event is under way now: https://www.sciencealert.com/we-re-pummeling-towards-a-dinosaur-ending-scale-mass-extinction-of-marine-life