[meteorite-list] Earth's Surface Transformed by ThreeMassiveAsteroid Impacts 3.2 Billion Years Ago

[Sterling K. Webb]

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.
> >
>
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