[meteorite-list] First Evidence For Early Meteorite Bombardment Of Earth

From: Ron Baalke <baalke_at_meteoritecentral.com>
Date: Thu Apr 22 10:00:10 2004
Message-ID: <200207250433.VAA06956_at_zagami.jpl.nasa.gov>

University of Queensland
Brisbane, Australia

25-Jul-2002

First evidence for early meteorite bombardment of Earth

University of Queensland researchers have for the first time
discovered terrestrial evidence of a meteorite bombardment nearly
4 billion years ago.

It is widely accepted that the moon was heavily bombarded at this
time, creating huge craters and basins. But although the effect
of these impacts is still clearly visible on the moon today,
movement of Earth's dynamic plates over geological time have
reshaped the terrestrial surface dramatically, leaving little
evidence of these catastrophic events.

In a paper published in the international journal Nature, UQ
researchers report evidence of the oldest impact events so far
discovered on Earth.

The research team of Dr Ronny Schoenberg, Dr Balz Kamber and
Professor Ken Collerson of UQ's new Advanced Centre for Isotope
Research Excellence (ACQUIRE) made the discovery by analysing
3.8 billion year old rocks from West Greenland collected by
Oxford University collaborator Professor Stephen Moorbath and
from Northern Labrador in Canada collected by Professor Collerson.

The researchers found these very old metamorphosed sedimentary
rocks -- derived from the Earth's early crust -- contain
anomalies in the isotope composition of the element tungsten.

"Such anomalies are usually found in meteorites. To our knowledge,
this is the first time these anomalies have been shown to exist
in terrestrial samples" Professor Collerson said.

"There is no plausible mechanism by which tungsten isotope
anomalies could have been preserved in the Earth's dynamic
crust-mantle environment. Therefore, we conclude these rocks
must contain a compound derived from meteorites."

"We have in effect found a chemical fingerprint in the earth's
oldest terrestrial rocks of a heavy meteorite bombardment 3.8
to 4 billion years ago," he said.

"This finding has implications for the origin of life on earth
as these giant impacts would have annihilated any possible
existing life forms but also delivered complex molecules from
carbonaceous chondrites -- a type of meteorite -- to the
earth's surface," Dr. Kamber added.

"Further research on this unique collection of rocks will yield
insight into the evolution of life on Earth provided provision
of adequate research funding," Professor Collerson said.

Media:

For more information contact

Professor Collerson
tel. 07 3365 8505, email: k.collerson_at_mailbox.uq.edu.au

Dr Kamber
tel. 07 3365 8580

Peter McCutcheon at UQ Communications
tel. 07 3365 1088
Received on Thu 25 Jul 2002 12:33:29 AM PDT