A massive asteroid impact, not volcanic activity, caused the climate change that wiped out the dinosaurs, new fossil evidence suggests. David Beerling at the University of Sheffield and colleagues analysed fossilised leaves from plants living before and after the extinction. The work suggests the amount of carbon dioxide in the atmosphere increased suddenly and dramatically 65 million years ago.
The increase was the equivalent of injecting at least 6,400 billion tonnes of carbon into the atmosphere, they say - enough to warm the Earth by as much as 7.5 degrees C and dramatically change the environment .
Other researchers have suggested that a series of volcanic eruptions at the Deccan Traps in India, dated to about 65 million years ago, might have prompted the climate changes that accompanied the extinction of 70 per cent of life on the planet. But only a massive asteroid impact - such as the one that left a 145 to 180-kilometre wide crater in the Yucatan peninsula in Mexico at about the same time - could have vapourised enough carbon-containing material in the Earth's crust to account for this rapid carbon dioxide increase, says Beerling's team.
As carbon dioxide levels in the atmosphere go up, plant's leaves have fewer pores, because it becomes easier for them to extract carbon dioxide from the air for photosynthesis. So by counting the number of pores on leaves from about 70 plants that were alive between 64 and 65.9 million years ago, Beerling's team could work out the concentration of carbon dioxide in the atmosphere at that time.
"We estimate that carbon dioxide levels were four or five times higher about 10,000 years after the impact," says Beerling. "For this much carbon dioxide to come from the Deccan Traps, all the eruptions would have had to come in that time window - but we know they took more like two million," he adds.
But Dewey McLean of Virginia Polytechnic Institute who proposed the volcano theory in 1981 is not convinced that Beerling can be so precise about the timing. "Their leaf database is so tiny as to be almost meaningless," he claims.
Journal reference: Proceedings of the National Academy of Sciences (vol 12, p 7836)
"We make choices everyday, some of them good, some of them bad. And - if we are strong enough - we live with the consequences."
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The location of the impact crater was already mentioned in the "NewScientist" article, posted by Althalus. Or can't you read? It's in the Yucatan Peninsula in Mexico.
But what wasn't mentioned was that the dinosaurs would have gone extinct even without any impact. Most dinosaurs at that time were on the verge of extinction before the impact. The asteroid impact only quickened the inevitable. The extinction of the dinosaurs actually started about 3 million years before the impact, except that it was a slow extinction and there were still several species of dinosaurs left when the asteroid impacted.