Re: Large animal extinctions - part 1

Michael Snyder (
16 Jul 1996 23:03:15 GMT

Dan Evens <> writes
> Thomas R. Holtz, Jr. wrote:
> > Except of course the seafloor has been radar mapped so that most large
> > scale surficial structures are well resolved.
> Sonar? I did not think microwaves moved very well through sea water.
> I think it's sonar backed up by spot checks using other methods.
> Picky quibble I admit. The sea floor has indeed been mapped out,
> at least well enough to spot a km sized crater.

Nope, radar is indeed the correct answer. Using satalites, the US. Navy
mapped the average height of the ocean's SURFACE, and then extrapolated from
that to the height of the sea bed underneath. It's a 3rd-order thing, really;
height of sea bed affects local mass density, which affects local
gravitational force, which affects height of ocean surface. This data has
only recently become available to the public (the Navy wanted it for submarine
navigation, and understandably didn't want to share it). It correlates well
with measurements taken by other means.