[MOL] Did cancer kill the dinosaurs? [01339] Medicine On Line

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[MOL] Did cancer kill the dinosaurs?

Did cancer kill the dinosaurs? 

By John Gribbin

Dinosaurs and other victims of mass extinctions could have been wiped out by 
epidemics of cancer triggered by massive bursts of neutrinos released by 
dying stars in our Galaxy, according to an American astrophysicist.

Other scientists have speculated that cosmic rays from supernova explosions 
could cause mass extinctions. But nearby supernovae happen too infrequently 
to explain the majority. So Juan Collar of the University of South Carolina 
in Columbia started looking at less violent stellar collapses, which generate 
large numbers of neutrinos.

Neutrinos are reluctant to interact with everyday matter. But if enough 
passed through the Earth in one go, then some would collide with the nuclei 
of atoms in living tissue. When this happens, the nuclei will recoil from the 
collision. Such recoils could damage DNA, producing cancer-causing mutations.

But how much damage, and how often? Collar has calculated that a 'silent' 
star collapse will occur within 20 light years of the Earth roughly once 
every 100 million years. Each stellar collapse will produce 19 000 recoils 
per kilogram of living tissue, and each recoil may deposit more than a 
thousand electronvolts of energy along a track 10 nanometres long. Collar 
compared the destructive potential of these recoils with conventional 
radiation damage. He suggests that a collapsing nearby star would produce 
about 12 malignant cells per kilogram of living tissue-each of which could 
trigger a tumour.

The effect would be particularly severe in larger animals because they have 
more tissue to become cancerous. And because neutrinos are not stopped by the 
outer layers of the body, the recoils they induce have what Collar calls the 
'aggravating factor' of taking place in sensitive tissue such as bone marrow.

Collar's calculations are relatively straightforward, but his conclusions are 
so astonishing that he has had a struggle to get them into print. He had to 
deal with comments from six expert reviewers before the paper describing his 
ideas was accepted by the journal Physical Review Letters, where it will 
appear shortly. Usually, papers go through just a couple of reviewers.

David Schramm of the University of Chicago, one of the main proponents of the 
supernova theory of mass extinction, agrees that these invisible collapses 
could, in theory, affect life in the way Collar suggests. The effect 'could 
be dramatic for at least one of the mass extinctions', he says. 

New Scientist, 13 Jan 96, Volume 149, Issue 2012. 

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