Relay-Version: version B 2.10 5/3/83; site utzoo.UUCP Posting-Version: version B 2.10.1 6/24/83; site dciem.UUCP Path: utzoo!dciem!mmt From: mmt@dciem.UUCP (Martin Taylor) Newsgroups: net.astro,net.space Subject: Re: Death Star? Message-ID: <768@dciem.UUCP> Date: Wed, 7-Mar-84 14:51:10 EST Article-I.D.: dciem.768 Posted: Wed Mar 7 14:51:10 1984 Date-Received: Wed, 7-Mar-84 15:59:39 EST References: <543@ihuxb.UUCP> Organization: D.C.I.E.M., Toronto, Canada Lines: 12 There was a recent article in Science referring to the periodicity of mass extinctions, and enquiring into the possibility of periodic large impacts. They searched for iridium anomalies (and other exotic elements or isotopes associated with meteorites) in sediments at extinction boundaries, but found none except at the well-known Cretaceous boundary. This doesn't deny the possibility of periodic massive impacts, but neither does it lend much support to the idea. (Sorry, I didn't keep the issue, and I don't have the reference, but it was within the last 6 weeks or so.) -- Martin Taylor {allegra,linus,ihnp4,uw-beaver,floyd,ubc-vision}!utzoo!dciem!mmt