h2g2 The Hitchhiker's Guide to the Galaxy: Earth Edition

Very interesting stuff - thanks for that

One question - the solar wind itself is pretty harmful stuff so I must say that's the first time I've heard of the Heliosphere being 'protective'. I can imagine however that if say proxima centauri went supernova (however unlikely ) it probably be more like a solar hurricane. Never heard that theory for some mass exinctions, .



Orcus

4 million years ago and 400 lightyears away seem awfully close and amzaingly recent for a supernova. Is there any geological evidence of this one like the iridium layer that the KT extintion bolide?

The evidence is there, but it is somewhat tentative, as this is a relatively new field of study. Some German scientists (Technical Institute of Munich) discovered two thin, globally distributed, layers of sediment in the ocean floor. They were enriched by an unusual isotope of iron (Iron-60) that *might* come from a supernova. The layers of sediment co-incide with what was called "mini-extinctions", about 2 million and 5 million years ago.

Also regarding your question on the proximity of supernovae, there is evidence that supernovae are not distributed evenly throughout the galaxy, but concentrated in regions known as OB Associations. As it happens, there is an OB Association close to the sun, the Sco-Cen Association, which is about 300 million light-years away, and it may have given birth to as many as 20 SN explosions in the last 11 million years alone. Also, the Sco-Cen Association was much closer to the sun a few million years ago than it is is today, meaning that we would be more likely to be negatively affected then than we do today.

Woodpigeon

I'd been taught before that a supernova within about 600 lightyears would sterilise the Earth, beyond "mere" ME events