Massive Volcanic Eruptions Wiped Out Half of Earth's Species at End of Triassic Period
At the end of the Triassic period at least half of the Earth's species, living on both land and in the ocean, went extinct. This paved the way for dinosaurs to take over and dominate for the next 135 million years. While scientists have suspected that massive volcanic eruptions were likely to blame for the mass extinctions, they had not been able to pin down the precise timing of the eruptions until now.
In a study published this week in the journal Science, researchers say that they've confirmed that eruptions that would have been large enough to bury the United States under 300 feet of lava occurred at the same time that large numbers of plant and animal species disappeared from fossil record.
Terence Blackburn, lead study author and a geologist at the Carnegie Institution for Science in Washington D.C., explained that 201 million years ago, tectonic forces forces began ripping the supercontinent known as Pangaea apart.
Blackburn said that the underlying mantle rock melted, which generated these large eruptions. The rift happened between sections of Pangaea that would go on to become North America and Africa. This also eventually created the Atlantic Ocean basin.
The huge eruptions, which are also known as flood basalt events, happened during four periods over the course of 600,000 years. The first round of volcanism, however, is what contributed to the extinction of so many different organisms.
The margin of error in calculating the timing of these eruptions ranged between one and three million years, which thus led to uncertainty over which happened first - the eruptions or mass extinction. Using a rare mineral known as zircon, which is found in igneous rocks like basalts, the scientists were able to narrow down their margin of error to 20,000 to 30,000 years, which put the initial eruptions to just before the mass extinction event.
When zircon crystallizes, it incorporates uranium, which decays over a known time with respect to the element lead. By measuring the ratio of uranium to lead in the samples, they were able to determine the age of the crystals.
Because Blackburn was able to accurately place the extinction event at the onset of the eruptions, climate modelers and other scientists may now able to pinpoint specific mechanisms like climate change that provoked the extinctions.
There is also evidence that the first round of volcanic eruptions doubled the amount of the carbon dioxide in the atmosphere, which led to increased global temperatures and ocean acidification. This happened pretty quickly, which did not give organisms much time to adjust.
Surprisingly, life did show signs of recovery during later eruption periods. The later eruptions did not result in as much laval as the initial eruption. Other researchers, however, have shown that the atmospheric carbon dioxide still increased after each event, which may have maintained climatic conditions present during the mass extinctions.
Researchers are unsure of how the species that did make it through the extinction were able to adapt to the new climate.