A mass extinction 200 million years ago caused a significant decline in species diversity, both marine and terrestrial. It allowed dinosaurs to make their debut on Earth before they too all became extinct.
Scientists have long attributed the end-Triassic extinction to volcanic activity. When they erupt, volcanoes spew huge amounts of sulfites into the atmosphere, blocking sunlight from entering the earth and warming it. The eruptions further disrupt the atmosphere when they cause warming in some areas where large amounts of CO2 trap heat in the process known as the greenhouse effect. But without more hard and fast evidence that eruptions occurred close to the extinction, scientists couldn’t be certain volcanoes were the direct cause of the end-Triassic die-out.
A study published March 21 in the journal Science puts a time period on the eruptions that is far more concrete than any estimate thus far. Terrence Blackburn from the Carnegie Institution for Science worked with a number of researchers to determine when exactly the ancient volcanoes erupted, and how close the eruptions were to climate change and mass extinction.
In ancient times, when all land was connected as the supercontinent Pangaea, volcanoes formed from what is now the northeastern US all the way to Morocco. Blackburn and colleagues employed a number of advanced methods of dating to study lava deposits at seven different sites all along what used to be this volcanic range. The team analyzed the lava deposits and charted radioactive decay of uranium isotopes to lead in zircon crystals found in them, thus coming up with a more precise date for the volcanic activity. The end-Triassic extinction, they determined, occurred 201.56 million years ago.
The volcanism, the research found, was closely timed with atmospheric and climatic changes. Over 600,000 years, there were four major eruption events, beginning in what is now modern-day Morocco and ending in New Jersey. The first of these, also the largest, was just around the time of the mass extinction.
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Analysis of lava deposits in New Jersey helped Blackburn and his team decipher when ancient volcanoes erupted.
The evidence of extinction is almost undeniable—beneath the layers of volcanic lava, the paleontologists found fossilized animal and plant pieces, but directly on top of the lava no such evidence of life was discovered. In addition, minerals that tell about the earth’s magnetic pole reversals indicate that the species die-out occurred at the same time across the world—the same time the volcanoes were overflowing with molten hot lava.
Find the research paper in Science. The Paleontological Research Institution, Ithaca, New York, is pleased to sponsor Paleontology content for This View of Life. Founded in 1932, PRI has outstanding programs in research, collections, and publications, and is a national leader in development of informal Earth science education resources for educators and the general public.
