An MIT-led team of researchers announced earlier this month (November 18, 2011) that massive die-outs both in the oceans and on land 252 million years ago – a period known to geologists as the “Great Dying” (the Permian-Triassic boundary) – took place in less than 20,000 years. That’s a blink of an eye geologically speaking. What’s more, the researchers also found that this time period coincides with a massive buildup of atmospheric carbon dioxide, or CO2, a greenhouse gas. They published their results in the journal Science in November, 2011.
In contrast to today, the group found that the average rate at which carbon dioxide entered the atmosphere during this time period – which was at the end of the Permian period – was slightly below the rate of carbon dioxide release into the atmosphere due to fossil fuel burning.
Dan Rothman of the department of Earth, Atmospheric and Planetary Sciences (EAPS) at MIT said:
The rate of injection of CO2 into the late Permian system is probably similar to the anthropogenic rate of injection of CO2 now. It’s just that it went on for 10,000 years.
The researchers suggest that – over tens of thousands of years – increases in atmospheric carbon dioxide during the Permian period likely triggered severe global warming, accelerating species extinctions. The cause of this increased CO2 is unknown.
The researchers also discovered evidence of simultaneous and widespread wildfires that may have added to end-Permian global warming, triggering what they deem “catastrophic” soil erosion and making environments extremely arid and inhospitable.
The first organisms appeared on Earth approximately 3.8 billion years ago. In the last 500 million years, Earth has undergone five mass extinctions, including the event 66 million years ago that wiped out the dinosaurs. And while most scientists agree that a giant asteroid was responsible for that extinction, there’s much less consensus on what caused an even more devastating “Great Dying” at the end of the Permian.
The end-Permian extinction – occurring 252.2 million years ago – eliminated 90 percent of marine and terrestrial species, from snails and small crustaceans to early forms of lizards and amphibians. This end-Permian extinction is the most severe mass extinction known in Earth’s history. It is thought to be the closest life has come to being completely extinguished. Possible causes include immense volcanic eruptions, rapid depletion of oxygen in the oceans, and – an unlikely option – an asteroid collision.
Sam Bowring, professor of Earth, Atmospheric and Planetary Sciences (EAPS) at MIT, spoke of the very short duration of the extinction, from a geologic perspective:
People have never known how long extinctions lasted. Many people think maybe millions of years, but this is tens of thousands of years. There’s a lot of controversy about what caused [the end-Permian extinction], but whatever caused it, this is a fundamental constraint on it. It had to have been something that happened very quickly.
Bowring worked with a group of American and Chinese researchers to pinpoint the extinction’s duration. The group analyzed volcanic ash beds from Meishan, a region in southern China where an old limestone quarry exposes rocks containing abundant fossils from the Permian period, as well as the very first fossils that signified a recovery from extinction during the Triassic period. The rocks of the region have been widely studied as the best global example of the Permian-Triassic Boundary (PTB).
The group collected clay samples from ash beds both above and below rock layers from the PTB. In the lab, they separated out zircon, a robust mineral that can survive intense geological processes. Zircon contains trace amounts of uranium, which can be used to date the rocks in which it is found. Bowring and his colleagues analyzed 300 of the “best-looking” grains of zircon, and found the rocks above and below the mass-extinction period spanned only a 20,000-year phase.
Bowring said now that researchers are able to precisely date the end-Permian extinction, scientists will have to re-examine old theories. For example, many believe the extinction may have been triggered by large volcanic eruptions in Siberia that covered two million square kilometers of Earth – an area roughly three times the size of Texas. He said:
In the old days you could say, “Oh, it’s about the same time, therefore it’s cause and effect,” but now that we can date [the extinction] to plus or minus 20,000 years, you can’t just say “about the same.” You have to demonstrate it’s exactly the same.
The group also analyzed carbon-isotope data from rocks in southern China and found that within the same period, the oceans and atmosphere experienced a large influx of carbon dioxide. Dan Rothman, who calculated the average rate at which carbon dioxide entered the oceans and atmosphere at the time, finding it to be somewhat less than today’s influx due to fossil fuel emissions, said the total amount of CO2 pumped into Earth’s atmosphere over this time period was so immense that it’s not immediately clear where it all came from. He said:
It’s just not easy to imagine. Even if you put all the world’s known coal deposits on top of a volcano, you still wouldn’t come close. So something unusual was going on.
Bottom line: MIT researchers published a study in November 2011 in the journal Science suggesting that the Great Dying – the mass extinction at the end of the Permian period, 252 million years ago – lasted only 20,000 years instead of millions of years. What’s more, they suggest it coincided with a period of increased CO2 in Earth’s atmosphere, comparable to today’s levels.
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