[meteorite-list] Mammoth Stew - first you cut up the Mammoth

From: E.P. Grondine <epgrondine_at_meteoritecentral.com>
Date: Wed, 19 Dec 2007 11:43:00 -0800 (PST)
Message-ID: <919269.44501.qm_at_web36913.mail.mud.yahoo.com>

Hi Sterling, Jason, all -

Concerning recent impacts (<12,000 years old), what
I've noticed over the years is that some people go
into denial, and those denial mechanisms are sometimes
really pretty bizarre. It's tough to accept on a gut
level that as things now sit you, your family, your
friends, everyone you ever knew or loved can be blown
off the face of the Earth in an instant without a
minutes warning. But that's exactly how it is, and
that's exactly what happened to some of our fellow
human beings in the recent past.

So, Jason, you wrote:

>Right, but seeing as the effects from the event of
>which we speak differ greatly from those of your
>comparison, it seems an unworthy one to make. Yes,
an >unknown phenomena might create such a set of
>as are geologically evident, but just saying "it's
>possible" is something that I acknowledge as well; we
>all know that Tunguska events occur and that,
>evidently, astronomical events that create the
>geological evidence that we've found occur. But that
>still in no way ties the two together.

Fact is, Jason, the Tunsguska impactor was viewed
coming in, and spherules from it have been recovered.
Sorry to disappoint you, but it wasn't a flying

Sterling, you wrote:

>Atmosphere not a factor in that size range.

Yes it is. Another factor in lunar crater distribution
is later coverage by dust and removal by later

Jason, you wrote:

>I don't know where you draw the 1km crater line, as,
>in my opinion, such a body might well break up if it
>entered the atmosphere at a shallow angle, but who's
>to say....

Well, airbursts can be more devastating then ground
hits, in terms of overall effect. We know compression
propagation in impactors, and 1 kilometer crater seems
to be a good guess as to airburst versus ground

Jason, you wrote:

> A thirty-degree impact is highly unlikely,

unsupported and most likely wrong.

> and I'm thinking that an iron impactor would do a
bit > more damage than a comet.

wrong. See airburst versus ground impact, above.

>Do you, by any chance, know what the composition of
>the dust layer (if it would suggest such a thing)
>points towards the composition of the body having

You're confusing two different impacts here, the iron
one at 31,000 BCE and the cometary one at 10,900 BCE.

>I just don't see much metallic residue coming from a
>comet, though I suppose there would be some.

It seems to me that the cores of the cometissimals in
a comet have a nice metal content. That's where the
iridium is, after all.

Sterling, you wrote:

> 5. You say, "most of the craters were formed before
> the [recent?] timeframe." Well, that's exactly what
> the argument's about, isn't it? This is the
> comfortable, "that's all in the past" argument.

You've got it: denial. Did I ever tell you the one
about Homo wushan?

Jason, you wrote:

>It's not all in the past, nor have I ever said such a
>thing. That said, there were more impacts two
billion > years ago than there are today, and you know
that as > well as I do.

Jason, if you're not in denial, then why try to make
statements about the recent impacts, and then divert
from the two impacts under discussion to the long term
impact rate?

Sterling, you wrote, most excellently:

>Let's review the cratering history of the solar
>system. After initial accretion, a tapering off.
>Then, at 3.8 to 3.9 billion years ago, an intense
>episode, the "Late Bombardment," followed by an
>exponential decline for more than 3 billion years.
>Then, at 0.6 billion years ago, cratering rates begin
>to rise dramatically, until 0.4 billion years ago,
>when they have increased fourfold in 0.2 billion
>years. They again decline. until 125-100 million
years >ago, when they increase, roughly doubling.

A great summary, which leaves us with significant
questions concerning meteorites and their parent
bodies - and answers which are only now gradually
being accepted.

> The role of comets, stellar encounters, Oort Cloud
> shenanigans, asteroidal family dustups is all
unclear > and yet to be pinned down. Good old

Yes indeed. Lack of science budget helps in this too,
as well as the behaviour of certain individuals
(ahem!) who control those budgets.

Jason, you wrote:

>What I'm trying to say is that given that there are x
>number of craters on the moon, we would need to know
>the age of each to determine a good number for the
>rate of impacts over the past, say, 50,000 years,
>which would be relevant to this discussion.

Undoubtedly this information will be provided by the
next series of manned landings on the Moon.

Jason, you wrote:

>Well, then climate change could well have been the
>culprit - but what cause the climate change is, I
>think, still open to discussion.

Actually, no it is not. That discussion has finished.
When you have a layer of extra-terrestrial material
and impactites such as has been demonstrated to exist,
fact replaces speculation.

>And that those iron bits, if they are from a
>meteorite, didn't come from the culprit that caused
>the climate change,

No one said they did, except you.

Two different impacts, two different impactors. One
that killed some mammoth, and another one that
extincted them. Two impacts.

good hunting all,
E.P. Grondine
Man and Impact in the Americas

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Received on Wed 19 Dec 2007 02:43:00 PM PST

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