Monday, April 29, 2013 12:00:58 PM
@Angilion: Yes, I'm far from "an expert" myself (as you may have suspected!).
The GRB (from a known source) was "backtracked" and seems to have been pointed at where the Earth was 400 million-odd years ago, killing off the trilobites... not entirely, just most of them. Could be coincidence of course! Not scheduled to happen again, ever, luckily!
The "supernova extinction" I read about a while ago. It`s just a theory (of course!) but there seems to be a link in one of the "lesser extinction periods" and a thin layer of "supernova residue". Since there`s been no supernovas close enough to (easily) explain that? They came up with 2 other theories. Multiple- and "Super-" supernovae...
Monday, April 29, 2013 11:31:53 AM
Hmm...this in interesting. There is a hypothesis that multiple supernovae in a group about 130 LY from Earth at the time might have temporarily damaged the ozone layer enough to kill off some surface plankton, which might have caused a higher than average rate of extinctions because plankton is at the bottom of a lot of food chains. That would match what you thought, if both the hypotheses are correct.
So maybe the astronomers I've read are understating the risk, or maybe the astronomers behind the above hypothesis are wrong. I`ve read their paper, but I don`t know enough to evaluate it. It`s well over my head.
Monday, April 29, 2013 11:12:30 AM
There's been lots of "mass extinctions" aside for the 4 or 5 that were HUGE eh?
Well...no. You used the term "one of the great extinctions" and there are 5 of them - the extinction level events. Although some people argue that we`re in the 6th one right now, given the effect that humanity has had since the industrial revolution.
[quote]The Gamma one being a BIG extinction and the supernova one being a "small" extinction... [/quote]
A supernova 200 lightyears away, if one happened, wouldn`t cause anything much on Earth. It wouldn`t kill anything, let alone cause widespread extinctions.
The last I looked, GRB was a hypothesis for the cause of one of the ELE, not a proven cause.