[meteorite-list] No Nemesis, yes; No periodicity, no.

From: E.P. Grondine <epgrondine_at_meteoritecentral.com>
Date: Tue, 2 Aug 2011 13:56:57 -0700 (PDT)
Message-ID: <1312318617.46919.YahooMailClassic_at_web36901.mail.mud.yahoo.com>

Hi Paul -

Raup and Sepowski's ELE data shows a roughly 26 million year periodicity.

As far as Earth craters go, aside from weathering, 70% of the planet is covered with water. Aside from that, there are many suspected structures which have not been examined. For example, there are three at the YD horizon, where impact is now accepted to have happened based on nano-diamond deposits and iridium levels.

As far as the "smaller" impacts go...

For a long time it has been assumed that after the LPBEs, there was a lessening of inner solar system accretion with time. This study would appear to indicate that some gravitational effects are just now coming into play.

I hope that new studies of Mars' craters and those on other bodies will finally lead to a general accretion model in which asteroidal and cometary impacts rates will be determined with some certainty.

E.P. Grondine
Man and Impact in the Americas
Received on Tue 02 Aug 2011 04:56:57 PM PDT