Re: More on the Antarctic impacts

[Tommy Tyrberg <tommy.tyrberg@norrkoping.mail.telia.com>]

><http://www.guardian.co.uk/life/science/story/0,12996,1286034,00.html>http://www.guardian.co.uk/life/science/story/0,12996,1286034,00.html

>The last paragraph is weird, though. For all that's known, magnetic field
>reversals happen totally at random, and how an impact could cause one --
>considering or not that Chicxulub does not correlate with one! -- is beyond
>me.


The whole story is weird. Impacts of that size would leave a global 
signature but nothing in particular happened 780 000 BP (except the field 
reversal). There is any number of marine and terrestrial profiles covering 
that interval and there is no shocked quartz, no spherules, no nothing. 
Impactors of that size would easily go through the ice and eject large 
quantities of bedrock globally (with an antipodal concentration, i. e. near 
the North Pole). Most of Antarctica is Precambrian shield so there should 
be plenty of quartz to shock.
Note that the much smaller Eltanin oceanic impact which occurred in the 
southern ocean c. 2 million years ago left a strong regional signature.

I suggest that either

a) The "impact craters" are something else

or

b) They are a lot older than 780 KY (there are for example some Late Eocene 
impact layers that have never been linked to a crater).

Tommy Tyrberg