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Re: More on the Antarctic impacts





><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