The Permian-Triassic (P/T) boundary, 252 million years ago: a whole new world
Marine life was almost wiped out 252 million years ago when nearly 95% of all marine species disappeared. In fact, the end of the Permian period saw the greatest mass extinction of the last 542 million years. Communities that had dominated during the Paleozoic Era disappeared. Many of the animals rooted to one spot, like stalked crinoids and brachiopods, were largely replaced by the more mobile mollusks, arthropods and echinoderms we see today.
What triggered this “Great Dying” or mass extinction that caused nearly 95% of all marine species to go extinct over a period of 200,000 years and most of them within 20,000 at the end of the Permian period? The victims included forests of conifers and tree ferns, big amphibians and reptiles that roamed among them, and a huge variety of fish and shellfish in the oceans. Trilobites and sea scorpions that plied the seas for hundreds of millions of years went extinct altogether.
Scientists have identified several possible explanations. Firstly, an asteroid: the impact of a huge asteroid or comet may have caused the extinction. A big enough collision could have affected the atmosphere and ocean chemistry for a long time afterwards. Secondly, too little oxygen: warmer temperatures might have slowed or halted the earth’s circulation which would have meant less oxygen-rich water being brought to the deep ocean, suffocating many animals. And thirdly, volcanoes. Massive carbon dioxide spewing volcanic eruptions in Siberia have been considered the most likely cause. Researchers thought the sudden rise in carbon dioxide would have acidified the oceans, killing off fish and shellfish – the biggest victims of the extinction — while changing the climate so fast that plants and animals on land also died out, unable to adapt in time[1].
However, a new study by researchers at the Massachusetts Institute of Technology in Cambridge, and the Nanjing Institute of Paleontology of the Chinese Academy of Sciences published in the journal Proceedings of the National Academy of Sciences in early April 2014 suggests that the key culprit in the extinction was a microbe called Methanosarcina that suddenly gained the ability to generate massive amounts of methane and release it into the seas and atmosphere at roughly the time of the mass extinction triggering a runaway greenhouse effect. Methanosarcina is a type of microbe called an archaea. While humans breathe in oxygen to generate energy and breathe out carbon dioxide as a waste product, Methanosarcina respires carbon-based compounds such as acetate, releasing methane as waste. This type of microbe still exists, and is responsible for making cows belch methane and for producing methane from rotting garbage in landfills.
The massive Siberian volcanic eruptions and consequent chemical changes coincided to dramatically change the climate and the chemistry of the ocean. The methane microbes then experienced an explosive growth spurt fueled by the mineral nickel which they found in sedimentary rocks from those Siberian eruptions. The nickel concentrations rose considerably just before extinction, which would have made a very favorable environment for the methane-producing microbes[2]. However, some scientist are skeptical that a single microbe played such a big role in the Permian extinctions. Pennsylvania State University geochemist Lee Kump says that the Massachusetts team have not proved for certain that this is what happened because they studied only one group of rocks from Southern China, and that if such a phenomenon did in fact lead to these extinctions, one would expect to see the result in rocks around the world[3].
Whatever the cause, it is not known how many species survived. Fossil-bearing rocks from the Early Triassic Period are poorly preserved, making evidence hard to find. We do know that surviving species often were widespread, suggesting that they had adapted to varied conditions which would have adequately helped them survive the upheaval.
[1] For the volcanic Large Igneous Province (LIP) explanation, see the previous page at /the-cambrian-and-post-cambrian-periods.html
[2] Article: “Methane-spewing microbe blamed in worst mass extinction”, 2 April 2014: http://www.cbc.ca/news/technology/methane-spewing-microbe-blamed-in-worst-mass-extinction-1.2595797. See also: Voice of America, 3 April 2014, article by Rosanne Skirble at http://www.voanews.com/content/microbes-trigger-largest-mass-extinction-ever/1885923.html; http://en.wikipedia.org/wiki/Permian%E2%80%93Triassic_extinction_event
[3] Carrie Arnold, “Microscopic Mass Murder – Microbes may be responsible for the largest extinction in Earth’s history”, Scientific American, July 2014, 11-12.
Scientists have identified several possible explanations. Firstly, an asteroid: the impact of a huge asteroid or comet may have caused the extinction. A big enough collision could have affected the atmosphere and ocean chemistry for a long time afterwards. Secondly, too little oxygen: warmer temperatures might have slowed or halted the earth’s circulation which would have meant less oxygen-rich water being brought to the deep ocean, suffocating many animals. And thirdly, volcanoes. Massive carbon dioxide spewing volcanic eruptions in Siberia have been considered the most likely cause. Researchers thought the sudden rise in carbon dioxide would have acidified the oceans, killing off fish and shellfish – the biggest victims of the extinction — while changing the climate so fast that plants and animals on land also died out, unable to adapt in time[1].
However, a new study by researchers at the Massachusetts Institute of Technology in Cambridge, and the Nanjing Institute of Paleontology of the Chinese Academy of Sciences published in the journal Proceedings of the National Academy of Sciences in early April 2014 suggests that the key culprit in the extinction was a microbe called Methanosarcina that suddenly gained the ability to generate massive amounts of methane and release it into the seas and atmosphere at roughly the time of the mass extinction triggering a runaway greenhouse effect. Methanosarcina is a type of microbe called an archaea. While humans breathe in oxygen to generate energy and breathe out carbon dioxide as a waste product, Methanosarcina respires carbon-based compounds such as acetate, releasing methane as waste. This type of microbe still exists, and is responsible for making cows belch methane and for producing methane from rotting garbage in landfills.
The massive Siberian volcanic eruptions and consequent chemical changes coincided to dramatically change the climate and the chemistry of the ocean. The methane microbes then experienced an explosive growth spurt fueled by the mineral nickel which they found in sedimentary rocks from those Siberian eruptions. The nickel concentrations rose considerably just before extinction, which would have made a very favorable environment for the methane-producing microbes[2]. However, some scientist are skeptical that a single microbe played such a big role in the Permian extinctions. Pennsylvania State University geochemist Lee Kump says that the Massachusetts team have not proved for certain that this is what happened because they studied only one group of rocks from Southern China, and that if such a phenomenon did in fact lead to these extinctions, one would expect to see the result in rocks around the world[3].
Whatever the cause, it is not known how many species survived. Fossil-bearing rocks from the Early Triassic Period are poorly preserved, making evidence hard to find. We do know that surviving species often were widespread, suggesting that they had adapted to varied conditions which would have adequately helped them survive the upheaval.
[1] For the volcanic Large Igneous Province (LIP) explanation, see the previous page at /the-cambrian-and-post-cambrian-periods.html
[2] Article: “Methane-spewing microbe blamed in worst mass extinction”, 2 April 2014: http://www.cbc.ca/news/technology/methane-spewing-microbe-blamed-in-worst-mass-extinction-1.2595797. See also: Voice of America, 3 April 2014, article by Rosanne Skirble at http://www.voanews.com/content/microbes-trigger-largest-mass-extinction-ever/1885923.html; http://en.wikipedia.org/wiki/Permian%E2%80%93Triassic_extinction_event
[3] Carrie Arnold, “Microscopic Mass Murder – Microbes may be responsible for the largest extinction in Earth’s history”, Scientific American, July 2014, 11-12.
It took 20 to 30 million years for ocean diversity to rebound after the Permian extinction – much longer than other recoveries. When a few species vanish, others can take over their roles, but when nearly 95% disappear, entire ecosystems are destroyed, and new species must evolve from the few survivors.
The Permian Triassic boundary interval in South China
This illustration from the Smithsonian Exhibition, Life and the Ocean, shows that the end Permian mass extinction was the second of two events, which had different effects on different groups of marine organisms.
The organisms referred to in the vertical columns which thereafter became extinct are (from left):
Trilobites (three lobes); rugose corals (refers to their wrinkled appearance);
Blastoids (an extinct type of stemmed echinoderm); fusilinids (a large group of extinct foraminiferans (single-celled organisms related to modern amoebas but having complex shells easily preserved as fossils); tabulate corals (an extinct form of coral, almost always colonial, forming colonies of individual hexagonal cells known as corallites defined by a skeleton of calcite, similar in appearance to a honeycomb);
Conodonts (extinct chordates resembling eels);
Ammonoids (the extinct class of molluscs called cephalopods, and so were related to the octopus, squid and pearly nautilus);
Brachiopods (a phylum of marine animals that have hard "valves" (shells) on the upper and lower surfaces, unlike the left and right arrangement in bivalve molluscs (such as scallops, clams, oysters and mussels);
Bryozans (moss animals, a phylum of aquatic invertebrate animals); crinoids (sea lilies);
Snails and clams.
The events referred to horizontally on the right hand side as having caused the extinction are:
This illustration from the Smithsonian Exhibition, Life and the Ocean, shows that the end Permian mass extinction was the second of two events, which had different effects on different groups of marine organisms.
The organisms referred to in the vertical columns which thereafter became extinct are (from left):
Trilobites (three lobes); rugose corals (refers to their wrinkled appearance);
Blastoids (an extinct type of stemmed echinoderm); fusilinids (a large group of extinct foraminiferans (single-celled organisms related to modern amoebas but having complex shells easily preserved as fossils); tabulate corals (an extinct form of coral, almost always colonial, forming colonies of individual hexagonal cells known as corallites defined by a skeleton of calcite, similar in appearance to a honeycomb);
Conodonts (extinct chordates resembling eels);
Ammonoids (the extinct class of molluscs called cephalopods, and so were related to the octopus, squid and pearly nautilus);
Brachiopods (a phylum of marine animals that have hard "valves" (shells) on the upper and lower surfaces, unlike the left and right arrangement in bivalve molluscs (such as scallops, clams, oysters and mussels);
Bryozans (moss animals, a phylum of aquatic invertebrate animals); crinoids (sea lilies);
Snails and clams.
The events referred to horizontally on the right hand side as having caused the extinction are:
- a drop in sea level (Pulse 1; 65% extinction);
- low oxygen; sulphur rich oceans; an eruption of food supply (Pulse 2: 95% extinction).