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Re: Supernova link to Rancholabrean fauna extinction?



On Fri, July 22, 2011 12:27 am, Dann Pigdon wrote:

>> The lengths that people will go to in order to say "it was anything but
>> humans"...
>>
>> This despite the great asynchrony of extinctions around the world, but
>> their close association with human arrivals; the fact that unlike all
>> other mass extinctions these are exclusively terrestrial macrofauna;
>> etc.
>
> Although it does make you wonder why humans chose to colonise new areas at
> those specific
> times.

Oh, there is no question that some of these colonization events are tied
into climate changes (e.g., main colonization of America south of the ice
happens after the deglaciation allows for migratino through the Ice Free
Corridor). But others simply tie in to the fact that humans, like any
species, actually *spread*: it takes time to move into boreal Eurasia
(need to have developed clothes) or Australasia (need to have invented
boats).

>Could they not have been 'climate refugees' forced to seek out new
> territories? Any sudden
> climatic changes would after all have affected humans as much as any other
> species - and a
> sudden influx of spear-happy hominids at the same time as local species
> were under climate-
> induced stress may have been more likely to cause extinctions than either
> of those pressures
> acting alone.

Absolutely. And so far as I have read, not one supporter of the
human-induced extinctions has argued that climate was not part of it.

> As far as the terrestrial extinctions are concerned; if supernova events
> were reducing O3
> coverage, then living underwater may have helped reduce the effects of an
> increase in UV
> penetration (as would being a nocturnal burrowing creature, for that
> matter).

Which would work if the extinctions happened at the same time worldwide.
But since the Australiasian one occurs tens of thousands of years earlier
than boreal Eurasia or the New World, it gets hard to argue for a
cosmogenic origin.

Thomas R. Holtz, Jr.
Email: tholtz@umd.edu   Phone: 301-405-4084
Office: Centreville 1216
Senior Lecturer, Vertebrate Paleontology
Dept. of Geology, University of Maryland
http://www.geol.umd.edu/~tholtz/
Fax: 301-314-9661

Faculty Director, Science & Global Change Program, College Park Scholars
http://www.geol.umd.edu/sgc
Fax: 301-314-9843

Mailing Address:        Thomas R. Holtz, Jr.
                        Department of Geology
                        Building 237, Room 1117
                        University of Maryland
                        College Park, MD 20742 USA