In the late Triassic, Earth experienced catastrophe on a scale without parallel in human history. About 200 million years ago, in just a brief heartbeat of geologic time, over half of all species on Earth vanished forever. Scientists have long tried to understand how so many species could have perished so quickly. Modern research has tied the late-Triassic mass extinction to some strange but devastating changes in Earth's atmosphere that took place at about the same time.
It's not entirely certain why Earth's atmosphere changed dramatically 200 million years ago. Scientists believe a series of large volcanic eruptions about 201 million years ago were the cause.
These eruptions left huge lava flows along the edges of the North Atlantic and released a lot of CO2 into the atmosphere. Huge quantities of this greenhouse gas triggered global warming, which in turn melted ice that contained trapped methane and led to further warming. Increasing CO2 concentrations would also have made the oceans more acidic, another possible cause of the mass extinction.
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Earth's atmosphere at the end of the Triassic contained the same kinds of gases it does today -- nitrogen, oxygen, CO2, water vapor, methane, argon and other gases in trace amounts. The concentrations of some of these gases, however, was very different.
In particular, Late-Triassic air contained the lowest oxygen levels in more than 500 million years. Less oxygen made it more difficult for animals to grow and reproduce and restricted their habitats. Higher elevations became uninhabitable because the oxygen concentrations at high altitude were even lower than those at sea level, too low for most animal species to tolerate.
However, CO2 concentrations were even more important. Scientists estimate two- or three-fold increases of CO2 levels over a relatively short period of geologic time. Eventually, they reached levels roughly four times the concentrations observed today. Carbon dioxide is a greenhouse gas; it can act like a blanket, trapping heat in the atmosphere, so Earth stays warmer than it would be otherwise. A rapid increase in CO2 concentrations could have caused major changes in Earth's climate, which might have brought about the mass extinction.
As CO2 levels jumped, rising temperatures could have melted methane-bearing seafloor ice deposits. The melted ice probably released large amounts of methane into the atmosphere over a relatively short period. Methane is an even more potent greenhouse gas than CO2. Studies by scientists at Utrecht University suggest that methane levels rose rapidly 200 million years ago. Overall, some 12 trillion tons of carbon in the form of either carbon dioxide or methane were released in less than 30,000 years. The Utrecht University researchers believe these rapid changes in the atmosphere probably brought about massive and rapid climate change which in turn may have led to the mass extinction.