|
|
Research on fossil leaves, published in the Proceedings of the National Academy of Sciences, suggests that global warming rather than an impact-produced winter may have been responsible for the extinction of the Dinosaurs and many other species 65 million years ago. Scientists from the University of Sheffield and Pennsylvania State University, US examined tiny pore holes preserved on fossil leaves from gingkoes and ferns which absorb and release carbon-dioxide. They found a sudden decrease in the number of pores on the leaves at the time of the extinction that suggests a five-fold increase in carbon-dioxide in the Earth's atmosphere. Carbon-dioxide (CO2) is an important greenhouse gas and such large quantites in the atmosphere would have raised global temperatures by as much as 7.5 degrees.
The research team believes that only the impact of a 10 km wide comet or asteroid could explain such a sharp increase in CO2. They estimate that the sudden vaporisation of between 6,400 and 13,000 billion tonnes of carbon from limestones in the shallow sea where the impact occurred was the source of the gas. Evidence from the fossil leaves also suggests that CO2 levels remained elevated for at least 10,000 years. Some scientists have previously suggested that gases released from huge volcanic eruptions in India may have changed global climate and caused the extinction. The new results, however, suggest a sudden increase at the time of the extinction is unlikely to have been caused by the eruptions since these took place over a period of 2 million years.
More info: BBC Online Article
|
