[meteorite-list] Earth's Surface Transformed by ThreeMassiveAsteroid Impacts 3.2 Billion Years Ago
From: Sterling K. Webb <kelly_at_meteoritecentral.com>
Date: Fri Aug 5 23:21:45 2005 Message-ID: <42F42C89.3FBB133_at_bhil.com> Hi, Tracy, List, The current theory of the Moon's origin is a grazing impact on the Earth by a Mars-sized (or better) object before 4410 millilon years ago. That date comes from the existence of the genesis zircon found in Australia a few years ago. The oldest date would be, well, pretty much the OLDEST date for anything from Earth or Moon, 4565 millilon years ago. The impact, as modelled by computer, doesn't have anything being "knocked off" the Earth. The impacting body fragments entirely and rebounds from Earth; the Earth's crust and mantle re-melts a second time, having gone through all this the first time it was formed; the iron core of the impactor sinks into the Earth and joins our core; the rest of the impactor and a lot of debris from the Earth end up in a disk around the Earth like Saturn's Rings only more so. All this stuff accretes into "the Moon" or is dispersed. That it was a real "hot" event is shown by the fact that the Moon is the driest body in the solar system, all water and gases driven off, and rich in "refractory" elements like titanium. In other words, about a billion years or more before the big impacts described below. Seems like the hits just keep on coming... Sterling Webb ----------------------------------------------------------- tracy latimer wrote: > Someone please refresh my memory -- about how long ago was the theorized > impact that tore loose the Moon from the proto-Earth? This sounds like it > happened after the Moon had coalesced enough to be a single solid. > > Tracy Latimer > > >From: Ron Baalke <baalke_at_zagami.jpl.nasa.gov> > >To: meteorite-list_at_meteoritecentral.com (Meteorite Mailing List) > >Subject: [meteorite-list] Earth's Surface Transformed by Three > >MassiveAsteroid Impacts 3.2 Billion Years Ago > >Date: Fri, 5 Aug 2005 11:47:36 -0700 (PDT) > > > > > >http://info.anu.edu.au/mac/Media/Media_Releases/_2005/_August/_050805glikson.asp > > > >Earth's surface transformed by massive asteroids > >Australian National University media release > >August 5, 2005 > > > >A cluster of at least three asteroids between 20 and 50 kilometres > >across colliding with Earth over 3.2 billion years ago caused a massive > >change in the structure and composition of the earth's surface, > >according to new research by ANU earth scientists. > > > > ______________________________________________ > Meteorite-list mailing list > Meteorite-list_at_meteoritecentral.com > http://six.pairlist.net/mailman/listinfo/meteorite-list Received on Fri 05 Aug 2005 11:20:41 PM PDT |
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