KT Event Effects Recorded In Fossil Leaves

[Richard W Travsky <rtravsky@uwyo.edu>]

http://news.bbc.co.uk/hi/english/sci/tech/newsid_2038000/2038599.stm

Fresh evidence to show an impact from space lay behind the demise of the
dinosaurs has been published by scientists.

The researchers say analysis of fossil leaves from 65 million years ago
shows there was a sudden and dramatic rise in carbon dioxide in the
Earth's atmosphere.

Only the impact of a large asteroid, vaporising billions of tonnes of
limestone rocks, could have released so much gas so quickly into the
environment, they believe.

Their calculations suggest the change in CO2 levels would have led to
catastrophic global warming, making it impossible for the ancient reptiles
and countless other lifeforms to continue. 
...
But suspicions still remain that a vast "flood" of lava and gas in India
at about the same time may have been the more decisive factor in
"poisoning" the planet's biology.

Now, researchers from the University of Sheffield, UK, and Southwest Texas
State University and Pennsylvania State University, US, have estimated
atmospheric carbon dioxide levels for the period.

They studied leaf fossils of gingkoes and ferns that grew around the time
of the dinosaurs' demise. 

The number of carbon dioxide-absorbing pores in the fossils reflects the
amount of carbon dioxide in the air: the fewer the pores, the more carbon
dioxide.

By using computer simulations and doing real experiments on plants, the
scientists can show there was a sudden, five-fold increase in CO2 at the
end of the Cretaceous.

This can only be explained, they believe, by the sudden vaporisation of
between 6,400 and 13,000 billion tonnes of carbon - a substantial
component of the limestone rocks that lined the shallow sea that existed
at Chicxulub 65 million years ago.

Such an injection of CO2 into the atmosphere could have created blistering
heatwave, raising global temperatures by as much as 7.5 Celsius. 

"We estimate that the CO2 levels were four to five times higher for 10,000
years after the impact," Sheffield's Professor David Beerling told BBC
News Online.

"The trouble with the [volcanism in India] is that it is spread over two
million years. If you release that much CO2 into the atmosphere at that
rate, the oceans will just suck it straight back out.

"So, the only thing that can explain such a large and sudden jump in CO2
would be this idea of a space impact." 
...