It Hit The Glacier.

[Minimalist]

http://www.eurekalert.org/pub_releases/ ... 120709.php

An international team of scientists led by researchers at the University of Hawaii at Manoa have found no evidence supporting an extraterrestrial impact event at the onset of the Younger Dryas ~13000 years ago.

Ice melts...crater vanishes.

[Rokcet Scientist]

http://www.eurekalert.org/pub_releases/ ... 120709.php

An international team of scientists led by researchers at the University of Hawaii at Manoa have found no evidence supporting an extraterrestrial impact event at the onset of the Younger Dryas ~13000 years ago.

Ice melts...crater vanishes.

Was that crater to have been in the ice sheet only then? Was it supposed to have not broken through the ice to shape a crater in the geology underneath it? That sounds like reaching to me.

[Minimalist]

The Laurentide ice sheet was supposed to be 8-10,000 feet high. You could make a significant crater in that.

[Rokcet Scientist]

The Laurentide ice sheet was supposed to be 8-10,000 feet high. You could make a significant crater in that.

Without affecting the underlying geology...?

Because if it didn't, that impact would have vaporized/dispersed ice/water only, no? So what would that have done to the global climate? It caused torrential rain and snow storms for months? (40 days...? ) Inundating large tracts of land and building up the ice sheet, away from the crater, even more?

[Minimalist]

Where is the crater for Tunguska?

[Rokcet Scientist]

Where is the crater for Tunguska?

Tunguska was an airburst, not an impact.

OTOH, even that is now doubted:



http://en.wikipedia.org/wiki/Tunguska_event

[Minimalist]

Tunguska was an airburst, not an impact.

Why could Firestone's comet/asteroid not have been an airburst as well?

[Digit]

Simply applying logic leads me to think that an extra terresial source is the most likely as it seems to me that the existance of a lake behind the leading edge of the ice can only have been coursed by 'impact' or vulcanism.
Anyone think of an alternative at all?

Roy.

[uniface]

Direct physical effects of it (small impact craters in chert) are found quite far from the epicentre - easily a thousand kilometers away. Which would indicate an airburst.

[E.P. Grondine]

We don't know yet with certainty what happened.

An impact into ice sheet appears to relieve tons of overburden, actually resulting in a circular uprise like the Kitscoty structure being formed.

An ice sheet impact does not exclude other smaller pieces air bursting.

From the KT impact, remember that multiple fragments can hit. From that one we have Chicxulub, and Shiva.

There is also the possibility that impact began a discharge of Lake Agassiz.

All I can do is point you to the memories which I collected together:http://forum.palanth.com/index.php/topic,1093.0.html

I have an image of a cast of a petroglyph which may have shown what occurred, but the original petroglyph and the site was lost to railroad construction in the 1890's.

As far as the iridium and other Platinum Group Elements, the amounts of these can vary greatly from comet fragment to comet fragment. The residual amounts are in parts per million or parts per billion, and the layer they are contained in can be very thin; its not the size of the impactor that gives it its energy, its its speed.

Those of you who are interested in impacts and man may enjoy reading through the links I posted in the introduction section. I hope you will forgive me the bald advertisement, but If you have not read my book yet, now would be a good time to PM me for a copy (it makes a great gift as well) or get a copy through interlibrary loan.

In closing, one catastrophe or cause does not mean that there was no other. Impact does not mean that emigration had no effect, or that Clovis tech had no effect, or the draining of Lake Agassiz, or solar variation, or nearby supernova.

In other words, we don't know with certainty yet.

It took 30 years for the Shiva crater to be found.

E.P. Grondine
Man and Impact in the Americas

[E.P. Grondine]

Where is the crater for Tunguska?

Tunguska was an airburst, not an impact.

OTOH, even that is now doubted:



http://en.wikipedia.org/wiki/Tunguska_event

Actually, Tunguska was an airburst. Estimates were that it was 15 megatons at 5.1 kilometers altitude. But like everything else impact related, the details are still being worked out.

I think that this image came from work that was done just last year.

[Rokcet Scientist]

From the KT impact, remember that multiple fragments can hit. From that one we have Chicxulub, and Shiva.

Are you saying both Chicxulub and Shiva were the result of one and the same 'encounter' of Earth with a meteorite? I'm not an expert, but I thought they were about a half million years apart...

[E.P. Grondine]

From the KT impact, remember that multiple fragments can hit. From that one we have Chicxulub, and Shiva.

Are you saying both Chicxulub and Shiva were the result of one and the same 'encounter' of Earth with a meteorite? I'm not an expert, but I thought they were about a half million years apart...

No. The best piece I read on the Shiva impact (in the Economist) indicated the nearly simultaneous (300,000 years at most) impact of two very large COMET fragments. That is why the world wide ejecta layer has the distribution that it does, and why the two impacts were not distinguished before.

meteorites are little pieces of asteroids and comets that fall to the Earth so some people can make a lot of money.

[Rokcet Scientist]

The best piece I read on the Shiva impact (in the Economist) indicated the nearly simultaneous (300,000 years at most) impact of two very large COMET fragments.

To call 300,000 years apart 'nearly simultaneous' is a stretch, imo.

[uniface]

Possibly over-scrupulous. Time lines change every several years as tools are improved, and the picture is far from being complete. Such is the nature of things.