At the end of the Permian Pangaea was born. Africa, Antarctica, Australia, South America and South Asia had long held together. It is probably rather obvious how Africa and South America were stuck together. These two continents’ coasts still clearly fit. Antarctica was attached to Africa at what is now Mozambique. South Asia was wedged between Africa and Antarctica. Australia was attached to Antarctica right beside South Asia. All other larger landmasses were gradually merged with each other. At the end of the Silurian, Europe and North America collided. Please note they were attached by the way of Greenland. During the first half of the Devonian North America collided with Africa and South America. What is now the US east coast was then attached to Africa. In the middle of the Carboniferous Siberia merged with China. Siberia then collided with Europe creating Pangaea.
Since there was only one continent the stretch of coast was relatively short. In addition, the size of the landmass made it hard for precipitation to reach large areas. Dry climate and few shallow seas was bad enough for life. But it would get worse. Large parts of Siberia were pierced by volcanic eruptions. Most of what they produced was lava solidifying underground. However, 1/5 was volcanic ash spreading through the air. These volcanic eruptions lit many layers of brown coal too. Each one of those layers could burn for millennia. In the short run the climate become colder due to all the visible smoke. The smoke being toxic did not help either. In the longer run it became warmer because carbon dioxide was released. The Earth’s average temperature rose by 17°C (9°F) over tens of thousands of years.
It not only became warmer and dryer at the very end of the Permian. The high fraction of carbon dioxide acidified water and soil. In water acidification caused many animals with calcareous shells to die. Acidified soil killed many plants which increased erosion rates. Increased evaporation caused by warming made bottom water rise. Both processes eutrophicated the seas and caused multiplication of until then surviving plankton. The breaking down of dead plankton absorbed too much of the seas’ oxygen. Large parts of the seas become hypoxic suffocating nearly all life. Sulfate-reducing bacteria took over and produced large amounts of hydrogen sulphide. This also killed life on land along the coasts of hypoxic seas. Eventually, the oxygen content of the air sunk to a little below current level.
This mass extinction was the largest occurring during the Phanerozoic. Sea scorpions and trilobites disappeared entirely as did the famous griffenflies. (Gigantic millipedes and scorpions were both already extinct.) Very many classes of animals lost more than half of their documented genera. Oftentimes it was more than 90%. Trees reproducing by spores went extinct at this point in time too. On the whole forest disappeared because surviving trees were too few. Immediately after this mass extinction the vegetation was dominated by lycophytes. Short episodes of increased volcanism continued well into the Triassic. Although they were not as devastating they caused repeated damage. These caused several turnovers between seed plants and lycophytes.
Even with the organisms which survived ecosystems become severely monotonic. One example I happen to know about is the distribution of land vertebrates. 90% of the fossils consist of a single genus. This is a type of proto-mammal named Lystrosaurus. Its members varied in length from 0.6 to 2.5 metres (2 feet to 8 feet 2). Despite them being herbivores they lacked molar teeth. I think they had the same strategy as our present day geese. Eat everything they can bit, squeeze out its juice in their digestive tract and pop out the rest. Anyway, we know they dung tunnels and hollows. This means they were adapted to cope with lower oxygen content. Moreover, they could hibernate. Both adaptations helped them to survive the mass extinction. Other surviving proto-mammals were mainly smaller carnivores. Some amphibians survived too, as did some lizard-like reptiles. The latter gave rise to the dinosaurs.
Uploaded on the 12th of August 2024.
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