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>This can't be right; that much water is the entire Atlantic basin.
>That's not mass extinction, that's the end of life as we know it. You
>think frogs will survive that? Turtles? Crocs? I don't think so.
>> Actually, I think the Chicxulub object was smaller -- which is a damned
>> good thing.
>Or the math is off. The crater's only a couple hundred kilometers in
>diameter even by the largest estimates, which is a heckuva lot smaller
Do the math.
The impression one gets from some posts is that a "mass extinction" means
that 95% of species are blown away, and the frogs, crocs, and mammals go
blissfully on their way. No. What it means is that probably 99.9% of
*everything* died. A few breeding pairs of crocs, frogs, etc. managed to
make it through the ensuing years or decades, then rapidly reproduced
because there was no competition. That is a more reasonable explanation for
why there is considerable randomness to the effects of mass extinctions. A
lot of the survival was not for any really good reason. Like the opposite
effect in the Cambrian explosion, a lot of it was just blind luck. Perhaps
smaller organisms did better simply because there were a lot more of them,
leaving more scope for luck.
As for the physics, I suspect that the size of Mars is a lot bigger than the
Atlantic Basin. A *lot* bigger. However, you're forgetting a number of
things. The impactor would have punched through the crust like so much
cardboard and dissapated a lot of its energy in the semi-fluid mantle,
effectively working against the entire volume of the Earth. Second,
v-square works in reverse. The impactor not only vaporized water, rock, the
odd dinosaur and what have you, it heated their molecules well *above* their
boiling points and gave them considerable velocity.
Let me paint a bit more detailed picture. The impactor goes through the
crust very quickly, making, as you observe, a relatively small crater and
doing not very much obvious damage. It finally dissapates its energy
heating and compressing the rock in the mantle. The mantle is only
semi-fluid so, after recoiling in surprise, some of that energy springs back
in the form of a high-pressure gas followed by low-viscosity molten rock.
(The rest decompresses outward, causing monster earthquakes over a very wide
area, or downward towards the core, doing not much of anything.) The
rebounding vaporized and molten rock is obviously at very high pressure, so
where does it go? Right. Back out the hole, blowing a somewhat larger hole
and dissapating its energy straight up, probably much of it on orbital or
very-long-range ballistic trajectories.
This accounts for a lot of the energy balance. However, if Alvarez is
right, look no further. This is many orders of magnitude more than every
nuclear weapon on Earth. One way or another, you can't let that much energy
loose near the surface of the earth without killing nearly everything.