Re: Comet impact in the Eastern United States - Feasibility of Evacuation

David DeLaney wrote:
> Bryan Derksen <bryan.derksen@[EMAIL PROTECTED]
> wrote:
>>> How many of these are sterilization events in the strict sense?  Would
>>> that gamma ray burst kill off creatures at deep-ocean vents or
>>> microbes living in rock?
>> Runaway greenhouse would probably do it, since the entire crust would 
>> wind up hotter than the boiling point. Earth would be Venus Lite.
> 
> Then the thermophilic bacteria get THEIR chance to sweep out from the
ocean
> vents and radiate.

There would be no oceans. Our runaway greenhouse scenario involves them 
boiling, since water va**** is itself a greenhouse gas.

>> Gamma ray bursts are overrated in terms of sterilization power, IMO.
The 
>> gamma rays can't penetrate the atmosphere so they won't cause any
direct 
>> effect, they get absorbed in the upper layers.
> 
> ... Someone isn't thinking about the same gamma rays that physicists
use. The
> atmosphere is by no means a perfect defense (tm White Wolf) against
gamma rays;
> it absorbs some, and some get through, and some cause huge particle
showers
> because they pass near enough to a gas-atom nucleus to interact with it.
> 
> Perhaps you're thinking about ultraviolet rays, absorbed (mostly) by the
ozone
> layer?

No, I was thinking gamma rays. I recalled that they were quite 
efficiently blocked by the atmosphere. Doing some websearching now to 
double-check that, I find that it's a little of column A and a little of 
column B; gamma rays are efficiently blocked by the atmosphere, but only 
about half as efficiently as ultraviolet. 
http://imagine.gsfc.nasa.gov/docs/introduction/emsurface.html
has a nice 
graph showing the penetrating power of various wavelengths.

So I guess if you pile enough gamma rays into the planet enough will get 
through to ruin peoples' day. But even if a typical GRB is likely to be 
able to put out enough, I already accounted for that in part of the post 
that you snipped; a gamma ray burst has a very brief duration so only 
one hemisphere of the planet would be directly exposed. So it's still 
not going to sterilize Earth.