A computer simulation of the Earth’s climate 250 million years ago suggests that increased carbon dioxide levels led to global warming that triggered the so-called “Great Dying”. The Great Dying was the largest mass extinction event on earth. It occurred approximately 251 million years ago and marks the boundary between the Permian and Triassic geologic periods, commonly known as the PT boundary. In less than one million years, approximately 96% of all marine species and 70% of all terrestrial animal species, paving the way for the dinosaurs’ eventual rise as the dominant animal group.

The massive PT extinction event has mystified scientists for decades and many potential explanations have been proposed, including an impact event with an extraterrestrial rock, plate tectonics and glaciation, extreme volcanic activity, a supernova, the sudden release of frozen methane hydrate from the ocean beds to trigger a greenhouse effect, or some combination of these factors.

This new research, published this week in the peer-reviewed journal, Geology, adds support to the hypothesis that increased carbon dioxide levels, which cause global warming, were the ultimate culprit. These new data show that extensive volcanism over the course of hundreds of thousands of years released large amounts of carbon dioxide and sulphur dioxide into the air, causing Earth’s temperatures to rise from 10 to 30 degrees Celsius higher than today, write the scientists.

“The implication of our study is that elevated CO2 is sufficient to lead to inhospitable conditions for marine life and excessively high temperatures over land would contribute to the demise of terrestrial life,” wrote Jeffrey Kiehl and his colleagues in their Geology paper. Kiehl and his colleagues are research scientists at the National Center for Atmospheric Research (NCAR) in Boulder, Colorado.

During the Permian-Triassic boundary, most of the continents were united into one large landmass, known as Pangaea (right). This is where the largest surface temperature increases were noted by the researchers (see image at top)

To carry out this work, the NCAR team used a research tool known as the Community Climate System Model (CSSM) which looks at the combined effects of atmospheric temperatures, ocean temperatures and currents. Their research showed that global temperatures rose so much that the oceans warmed to a depth of about 3,000 meters (10,000 feet), particularly in the higher latitudes. The increased oceanic temperatures interfered with circulation that carries colder water, rich in oxygen and nutrients, into oceanic depths. As a result, the earth’s oceans became depleted of oxygen and were unable to support marine life.

Sources:

BBC News, story, quotes.

Extinction by Douglas H. Erwin (2006).