[ExI] Fermi Paradox and GRB bursts

[John Clark]

On Thu, Oct 2, 2014 at 5:06 AM, Anders Sandberg <anders at aleph.se> wrote:

> Yes, I have read the paper and still remain unconvinced. Destroy the
> ozone layer and the land biosphere is in trouble. But do you really think
> that will wipe out fish all the way to the bottom of the Marianas trench?
>

It wouldn't sterilize the planet but it would cause lots of trouble. During
the last 600 million years the Earth may have been hit by one massive Gamma
Ray Burst and it may have caused the Ordovician–Silurian mass extinction
450 million years ago. At that time the land biosphere hadn't even evolved
yet, nevertheless except for the Permian it was the largest mass extinction
in Earth's history. If you were near the center of the galaxy it seems
reasonable to me that your chances of being hit by a similar GRB would be
at least 10 times larger (maybe 100) as it is on the Earth, and that could
be a big roadblock to the evolution of life complex enough to make radio
telescopes.  In addition you'd be much more likely to be uncomfortably near
to a run of the mill supernova or a belch from the super-massive Black Hole
at the Galaxy's center.

If you're too far from the center (like in the galactic halo) that could be
a problem too, there wouldn't be enough of the heavier elements that life
needs, or even enough to make rocky planets like the Earth, so you'd only
have gas giants such as Jupiter. For this reason some have proposed there
is a Galactic Habitable Zone.

  John K Clark
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