About 200 million years ago, around half of Earth's species quickly vanished, due to the eruption of massive volcanoes, according to a new study published in the journal "Science."
At that time, land on Earth was consolidated into a large supercontinent called Pangaea. The eruptions, forming what is known as the Central Atlantic Magmatic Province, spanned from present day New Jersey to Morocco and lasted for over 600,000 years, creating a rift that later became the Atlantic Ocean. At the time, the planet was populated by crocodile-like creatures and squid-like mollusks, but the eruptions paved the way for a number of new species, including dinosaurs. It was the largest biological shift in Earth's history.
Scientists previously suspected that volcanic activity was responsible for the mass extinction, known as the End-Triassic Extinction, but were unable to correlate the two events with certainty. Now, however, they are able to determine that the events occurred at roughly the same time, by matching the fossil record with dense basalt formed by the eruptions. More specifically, they were able to extract rare zircon crystals from the basalt formations and measured lead and uranium traces, which they then tested for radiometric dating.
Finding and analyzing the zircon crystals was no easy task. Columbia University geologist Paul Olsen managed to mine one from a New Jersey highway exit not far from his home. Still, the scientists were able to narrow the margin of error for dating the lava to between 15,000 and 22,000 years, a remarkable feat.
"People have long suspected that flood basalts had caused the extinction event, but the problem was there was an uncertainty of one to three million years," says lead author of the study geologist Terrence Blackburn of the Carnegie Institution in Washington. According to UC Berkeley geochronologist Paul Renne, the new findings put "a sharper tip on that pencil."
"It says all this stuff is true and here's when it happened," Renne says.
While it now appears clear that the volcanic eruptions coincided with the End-Triassic Extinction, it is still unclear how exactly the animals died as a result of the eruption. One possibility is that many of Earth's creatures would not have been able to withstand the dramatic temperature shift that resulted from carbon dioxide release from the volcanoes.
The results of the study are "a nice confirmation of what we and others have been aware of for some time," Renne told LiveScience. "The main difference is the dating that they used is more precise than our results were."
