Sometimes I’m asked if astronomy really does anybody any good — aside from astronomers, that is. I am always pleased to point out that most science does humanity some good, expecially if we pay attention to the results! Latest case in point is the never-ending saga of mass life extinctions on the early Earth. We all know about the death of the dinosaurs ‘way back when, but there’s clear evidence in the fossil record that life has been nearly wiped out several times since this old planet coalesced out of the primordial solar nebula. About 440 million years ago, in a geologic period called the late Ordovician, the second largest die-off of life occurred. About two-thirds of all species were wiped out. Hardest hit were the life forms that lived on or in shallow water. Deepwater organisms were hardly affected at all. The culprit? Astronomers think that increased ultraviolet radiation was somehow admitted through Earth’s atmosphere in higher-than-usual amounts. This would serve to fry exposed life while not even bothering the buggies and critters hidden on the seafloor muck. What happened to the Earth’s atmosphere? Usually it’s pretty good about protecting the planet from UV — but, it’s possible that a gamma-ray burst from a relatively nearby star that had exploded as a supernova and ultimately formed a black hole might be the culprit. Such a blast within 10,000 light years of the planet woul dbe enough to damage our atmosphere, introduce such pollutants as nitric acide rain, and seriously harm the ozone layer — the last line of planetary defense againsts lethal UV radiation.
We’re just now starting to understand the mechanism of gamma ray bursts — in a few moments they send out so much light and radiation they can frequently outshine the galaxies where they live. So, it doesn’t take much of a stretch to imagine what would happen to our planet if one happened nearby.
Did this happen? There’s a lot of evidence in the fossil record. It would be neat to find a smoking gun supernova/black hole candidate — but in 600 million years, there are bound to be a lot of them that fit the bill. Singling out just one or two would be nearly impossible. But it’s a neat theory and yet another data point to consider as we look for cosmic influences on our little watery globe.