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Impact craters may be cradles of life

 Lappajarvi crater

The southern part of Finland's lake Lappajarvi is an ancient asteroid or comet crater providing the first direct evidence on impact cooling rates (Source: NASA/MPorciusCato)

Life begins in craters Craters caused by asteroid or comet impacts may have played an important role in the creation and evolution of life, say Australian scientists.

Their study, published in the journal Geochimica et Cosmochimica Acta, found the heat generated by hypervelocity impacts, takes hundreds of thousands of years longer to dissipate than existing models anticipated.

Slower cooling times combined with the right chemical ingredients provide ideal environments for the evolution of microbial life, says Dr Fred Jourdan from Curtin University and Dr Martin Schmieder from the University of Western Australia.

"Now that we know you get cooling times of a million years and more, craters become a very good place to look for signs of life on Earth and possibly on Mars too," says Jourdan.

Jourdan and Schmieder studied Finland's 23-kilometre-wide Lappajärvi crater to determine its exact age.

"Impacting asteroids and comets generate enormous amounts of heat, melting surrounding rocks," says Jourdan.

The scientists compared the ratios of two different argon isotopes to measure the age of different minerals formed on impact.

"These decay at specific rates, telling us the impact occurred 76 million years ago."

"However, we noticed minerals of potassium-feldspar looked a bit weird with a fractured structure like a sponge," says Jourdan.

Testing of the potassium-feldspar revealed it was between 600,000 and 1.5 million years younger than the rest of the rocks in the impact crater.

"The fractured structure meant the potassium-feldspar took longer to cool."

Previous crater cooling models based on theoretical simulations, were far shorter, predicting rates of about 10,000 years after impact.

But the time difference between impact and potassium-feldspar recrystallisation shows the Lapparjärvi crater did not cool down for up to a million years or more, says Jourdan.

"That was completely surprising, we were expecting everything to give the same age because an impact is an instantaneous event," says Jourdan.

Chemistry of life

The scientists believe the longer crater cooling period combined with the chemical soup of material contained in the impact structure could provide the time needed for the building blocks of life to come together.

"One of the really interesting things is phosphorous, which is everywhere in an oxidised form," says Jourdan.

"But the heat generated by an impact event can [change] it into an un-oxidised form, which is the same as the phosphorous found in both RNA and DNA."

"So if you put the right mix, phosphorous, carbon and water you can create life," says Jourdan.

Mars' Gale Crater, which once held a lake, is an ideal place to search for the chemical signs of past or present life, he adds.
