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STS-120 day 2 highlights

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Did prehistoric asteroid smash stimulate life?

BY KULVINDER SINGH CHADHA

ASTRONOMY NOW

Posted: 22 December, 2008

Microscopic meteorite fragments discovered in Scotland that fell 480 million years ago coincided with a time of dramatic upheaval on Earth. This suggests that a rain of meteors 100 times greater than normal caused upset on the Earth’s surface and maybe even stimulated life in the oceans. However, any such link is far from proven.


The fragments were found in limestone rock just outside the village of Durness in north-west Scotland by scientists from the University of Aberdeen. Professor John Parnell of the School of Geosciences says, “There were two parallel studies going on and one was to look for meteorites, based on the unusual result in Sweden.” Parnell also looked at the geological record in many parts of the world and found that, “the continental margins [at the time] were experiencing chaos.” That is, there were landslides and disruptions at the coastal areas of the world.

Microscopic image of a micrometeorite, a hundredth the size of a grain of sand, dissolved out of limestone from Durness, NW Scotland. The micrometeorite landed nearly 500 million years ago during a period of intense meteorite bombardment. Image: courtesy Ian Dredge, University of Aberdeen and Royal Holloway University of London.


The four and a half-year-old Swedish study that Parnell refers to was conducted by Philipp Heck et al at the University of Lund. It found a preponderance of meteorite grains in 480 million-year old sediment that suggested a sustained ‘rain’ of meteors at this time. Heck’s team concluded that this could have been the result of a collision in the Asteroid Belt.


The fact that a large number of grains have been discovered in Scotland, in rock from the same geological time period, gives strong support to the idea of a lasting, global-wide phenomenon. But what kind of grains are they? Parnell says, “They are iron spherules, which are the result of a high-temperature transit through the atmosphere.” Only ten percent of meteorites are iron. Parnell’s team dissolved the rock in acid and extracted the fragments magnetically.


If indeed the fragments tell of a collision in the Asteroid Belt, could such a thing occur again? Should we be worried? Reassuringly, Parnell says, “You can never say never. But the fact is, nothing on that scale has happened in the 480 million years since. It’s very unlikely to happen in the next few million years.”


And there may be even less reason to worry about meteor rain affecting life. During the time the fragments fell, in the Ordovician period, something at least seems to have stimulated the expansion of life forms (which at that time only existed in the oceans). Though there seems to be a link with the meteor rain, Parnell says, “There was a lot of volcanic activity during that time, and some are linking that to the meteors. However, I am not doing that myself.” There is no known mechanism that links meteors to volcanism. It may well be then that the upheaval which stimulated life in the oceans was more closely related to volcanism, and the meteor rain may well have been just an amazing coincidence. Only time and more data will tell us for sure.

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