[FPSPACE] Comets and ice-age extinctions

[David Portree]

Larry:

 

No, though I doubt that they would in any case. Human population estimates for North America for that period vary widely, but they were above all low. I personally don't believe a human die-back could be detected because the sample population was too low. Changes in human culture are sometimes cited as evidence of a die-back, but human culture just changes sometimes. The low population makes the overhunting hypothesis harder to defend. It's a fascinating mystery and it will be a while before it's sorted out.

 

Myself, if I were looking to vehemently defend a megafauna extinction cause with little evidence to support it, I'd lean toward diseases brought in from Asia. I think that climate change was probably enough to do the job, though. "Perfect storms" of multiple causes are dramatic - love those fiddly interrelationships - but probably not necessary.

 

A (not very original, I expect) question occurred to me - if the Earth is being pummeled by comets, then why don't we see more evidence on the moon? As far as I can tell, apart from some anomalous features traditionally attributed to comet impact mainly because no one knows what else to do with them (Reiner Gamma, for example), there's little clear-cut evidence that comets have struck the moon at all (though I expect that they must have). There's certainly no evidence that they've struck the moon more frequently in the past three or four billion years than have sizable asteroids (that is, not all that often - once in a species lifetime). 

 

I think that the SL9 event of 15 years ago - the impact series ended 15 years ago today - was not a sign that such events are a lot more frequent than is widely assumed, but rather that we were highly privileged to witness it. That's the coolness in all this. These things are rare as civilizations and even species count time, and wildly improbable on the scale of a human lifetime. And our species, our civilization, our *generation*, had a front row seat. Whoa. 


David S. F. Portree

dsfportree at hotmail.com
dportree at usgs.gov
 
http://robotexplorers.blogspot.com/
http://beyondapollo.blogspot.com/
 
http://astrogeology.usgs.gov/About/People/DavidPortree/
 



 
> From: ljk4 at msn.com
> To: Kosmos327 at aol.com; fpspace at friends-partners.org
> Date: Wed, 22 Jul 2009 02:21:32 +0000
> Subject: Re: [FPSPACE] Comets and ice-age extinctions
> 
> Have archaeologists found masses of unburied skeletons human and animal in North America dating from that era?
> 
> Larry
> 
> 
> Sent via BlackBerry by AT&T
> 
> -----Original Message-----
> From: Kosmos327 at aol.com
> 
> Date: Tue, 21 Jul 2009 18:36:49 
> To: <fpspace at friends-partners.org>
> Subject: Re: [FPSPACE] Comets and ice-age extinctions
> 
> 
> Hi Dave, 
>   
> It would appear to me that you are basing your conclusion on what is presented in this story (which is definitely poorly written) and not on the study itself. The study which was just released (perhaps a preview was released weeks or months ago) has not had time yet to be rejected by other credible scientist. 
>  Heck, the study itself might just contain the evidence this jury you referred to has been waiting for. 
>   
> Just a though. 
>   
> David L. Rickman 
>   
> In a message dated 7/21/2009 12:26:11 P.M. Eastern Daylight Time, dsfportree at hotmail.com writes: Peter:
>  
> Didn't this come out several weeks (months?) ago? I wonder why they're trotting it out again. Maybe a tie-in to the black spot on Jupiter, though we all know that that is a sign that the planet is being stellified.
>  
> The headline contradicts the contents of the story - never a good sign. There's a lot of doubt out there in the community about this interpretation of the data. Heck, that there was a human die-back at the Younger Dryas is up for debate. And, most quaternary scientists I know are perfectly happy with assigning responsibility for the megafauna die-off to climate change (mainly) and overhunting (though that remains more controversial). No third cause needed. If impacts did occur, why comet impacts? In the story they say "comet-like objects." What does that mean? Asteroids? 
>  
> This doesn't mean that this interp is wrong, necessarily, just that the jury is still out. My criticism here is aimed at the news story, not at anyone posting here or their deeply held beliefs.
> 
> David S. F. Portree
> 
> 
>  
> 
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