The Pre-Dinosaur Extinction Happened 252 Million Years Ago
The Great Dying. When an estimated 95% of marine species went extinct. It happened 252 million years ago and no, it was not the great dinosaur extinction of the Cretaceous period, but rather one with far greater catastrophic consequence: the Permian Extinction. Not only marine life suffered; an unknown percentage of land dwelling species also succumbed, possibly up to 95%, in what is known as the most severe of our planet’s five large extinction events.
There are Many Hypothesis as to What Caused the Pre-dinosaur Extinction
Scientists still speculate as to the cause of the great Permian Extinction. Hypotheses include a devastating eruption by a volcano; an asteroid strike similar to the one that killed off the dinosaurs during the Cretaceous; and oxygen-depleted water welling up from the deepest ocean.
Recent studies, based on careful examination of fossils from the time of the pre-dinosaur extinction, suggest new ideas in interpreting the past, and ways of interpreting the future of modern marine organisms. By studying organisms at the cellular level, two scientists managed to elucidate the inner mechanism that killed off certain marine animals, while others survived.
Theories of the Pre-dinosaur Extinction Suggest a Predisposition to Extinction
Earth scientist Matthew E. Clapham and geochemist Jonathan L. Payne, from UCLA Santa Cruz and Stanford respectively, studied ca. 50 000 fossils of marine invertebrates from 8 900 Permian collections before concluding that the presence of calcium carbonate shells or skeletons predisposed a species to extinction. Animals with different skeletal substance, or those with ways of keeping their internal chemistry intact, stood a better chance at survival. A creature’s diet, mode of transport, a large distribution range or large numbers of individuals, did not protect it since deaths occurred across the whole ocean.
Rather, a combination of stress-factors that occurred with rapid succession created a cumulative effect on many marine animals, e.g. an absence of dissolved oxygen in the water, excessive carbon dioxide levels, changes in ocean acidity, impaired ability to lay down calcium carbonate shells or skeletons, and increased ocean temperatures. Within the relatively short geological period of 200 000 years, or less, these factors completely changed the suite of dominant marine animals.
Corals Suffered Most in the Pre-dinosaur Extinction
Corals suffered most in the pre-dinosaur extinction, with many groups disappearing completely, e.g. the horn-shaped rugose corals that lived on the ocean floor. Despite once being common, all trilobite species disappeared. Sea sponge diversity took a knock, as did shelled reef and sea species from the Permian. All major marine groups of invertebrates, as well as protists (mainly one-celled micro-organisms) suffered losses.
Gastropods Became the Dominant Group After the Pre-dinosaur Extinction
After these major losses the gastropods became the dominant ocean group, e.g. bivalves such as clams, and the snails. This shift after the Permian extinction is directly responsible for the marine assemblage we see today.
What, then, caused the marine animals such physiological stress? Clapham and Payne reach the conclusion, in a second paper, that the global carbon cycle was disrupted by an injection of carbon into the ocean and atmosphere. The selective nature of extinctions cannot, however, be explained by theories of asteroid impact, or oxygen-deprived water welling up from the sea floor. The suspect is volcanic in nature – the biggest event of its kind during the past 500 million years – the eruptions responsible for the stair-like region in northern Russia (the Siberian Traps). These are believed to have sent enormous quantities of carbon gas into the atmosphere and oceans, which caused long-term phenomena such as acidification and warming of the oceans, as well as large tracts of oxygen-poor water in the ocean.
Chemistry Changes Could Have Contributed to the Pre-dinosaur Extinction
According to Andrew H. Knoll, a geologist from Harvard, this idea that ocean chemistry changes (such as acidification) affects mass extinction, is a relatively novel idea. His 1996 paper explored the consequences of rapid atmospheric carbon dioxide increase on organismal physiology. He noted that the present situation and predictions for the next 200 years might mirror what we believe happened in the past.
Today’s Ocean Climate is Similar to that of the Pre-Dinosaur Extinction
Likewise, Clapham was astounded by the match between the Great Dying and the current trend seen in ocean chemistry, with high levels of atmospheric carbon-based gases causing ocean warming, acidification and dead zones with low oxygen. He cautions that these situations are not exactly the same, since the ocean was more easily acidified during the Permian than now – deep-water calcium carbonate that off-sets acid was less abundant in the past. Yet, corals are as vulnerable today and they were in the Permian, since their internal chemistry makes them reliant on calcium carbonate for reef building.
This is echoed by Chris Langdon, a biologist from University of Miami, whose pioneering research on ocean acidification, shows that corals are in dire straits worldwide. He recently studied coral reefs with naturally high acidification in Papua New Guinea, showing that coral cover declines drastically when acidity reaches the levels that are predicted for the end of the century. Branching corals that provide shelter for fish species are at particular risk.
The work of Hans Portner, animal ecophysiologist at the Alfred Wegener Institute, Germany, reveals that an ocean with increased temperature and higher acidity, causes negative effects on the physiology of present-day marine animals. He looks to the Permian extinction as an archive for predicting how modern species will cope with increased carbon loads. He also cautions that the two periods are not quite similar, since Pangea, the single supercontinent of Permian times, had different ocean currents than today. Carbon is also currently entering the atmosphere at much faster rates than during the Permian.
Knoll sums it up. Humans, today, are as good as volcanoes at releasing carbon into the earth’s atmosphere.
Will we experience the next Great Dying like the pre-dinosaur extinction soon?