Did cancer kill the dinosaurs?
http://www.newscientist.com/nsplus/insight/rexfiles/cancer.html
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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