Re: Large animal extinctions
Timo Niroma (timo.niroma@tilmari.pp.fi)
17 Jul 1996 20:39:49 GMT
In article <4sh73j$e1d@news.next.com>, msnyder@NeXT.com (Michael Snyder) says:
>
>Dan Evens <dan.evens@hydro.on.ca> 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.
Now I think we are talking about the same map.
But what I have heard of it, its resolution is about 10 km.
And a crater to be discernible from other constructions, it should have a still
wider diameter than 10 kilometers.
And to prove it's a meteorite crater we should dive to it.
By the way, somebody said that the comets come more likely in the plane of
ecliptica.
If they are from Kuiper belt, it is still possible, that there is some bias towards
the ecliptica, but if they come from Oort cloud, anything is possible.
Craters during the last 12,000 years, latitude, degrees (N=North, S=South):
Aorounga N19
Campo Del Cielo S27
Haviland N38
Henbury S25
Ilumetsa N58
Kaalijarvi N58
Macha N60
Morasko N52
Sobolev N46
Wabar N21.5
North is more common because there is more continental area north of the equator.
Regards,
Timo
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