[meteorite-list] "Young" chondrules discovered in Gujba and an HAH

From: Pete Pete <rsvp321_at_meteoritecentral.com>
Date: Thu Aug 18 20:31:28 2005
Message-ID: <BAY104-F30C3774D3DE9A2011D9DDDF8B50_at_phx.gbl>

I'd really like to hear some thoughts about this from the pros on this list.

With so many studies of so many meteorites for so many years, you'd think
there would have been an inkling before this about an age controversy of
chondrules.

Pete


From: Darren Garrison <cynapse_at_charter.net>
Reply-To: cynapse_at_charter.net
To: Meteorite Mailing List <meteorite-list_at_meteoritecentral.com>
Subject: [meteorite-list] "Young" chondrules discovered in Gujba and an HAH
Date: Thu, 18 Aug 2005 18:57:21 -0400

http://www.news.utoronto.ca/bin6/050818-1567.asp

Discovery of 'young' material in meterorites defies linear theory of solar
system's origin
>From order to disorder: A monkey wrench in solar system evolution?
Aug 18/05
by Sonnet L’Abbé
A U of T scientist has found unexpectedly ‘young’ material in meteorites
– a discovery that breaks
open current theory on the earliest events of the solar system.

A paper published today in the August issue of Nature reports that the
youngest known chondrules –
the small grains of mineral that make up certain meteorites – have been
identified in the meteorites
known as Gujba and Hammadah al Hamra.

Researchers who have studied chondrules generally agree that most were
formed as a sudden,
repetitive heat, likely from a shock wave, condensed the nebula of dust
floating around the early
Sun. Thinking that an analysis of the chondrules in Gujba and Hammadah al
Hamra would be appropriate
for accurately dating this process, U of T geologist Yuri Amelin, together
with lead author
Alexander Krot of the University of Hawaii, studied the chondrules’
mineralogical structure and
determined their isotopic age. “It soon became clear that these particular
chondrules were not of a
nebular origin,” says Amelin. “And the ages were quite different from
what was expected. It was
exciting.”

Amelin explains that not only were these chondrules not formed by a shock
wave, but rather emerged
much later than other chondrules. “They actually post-date the oldest
asteroids,” he says. “We think
these chondrules were formed by a giant plume of vapour produced when two
planetary embryos,
somewhere between moon-size and Mars-size, collided.”

What does this mean in the grand scheme of things? The evolution of the
solar system has
traditionally been seen as a linear process, through which gases around the
early sun gradually
cooled to form small particles that eventually clumped into asteroids and
planets. Now there is
evidence of chondrules forming at two very distinct times, and evidence that
embryo planets already
existed when chondrules were still forming. “It moves our understanding
from order to disorder,”
Amelin admits. “But I’m sure that as new data is collected, a new order
will emerge.”

Financial support for this project was provided by NASA and the Canadian
Space Agency
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Received on Thu 18 Aug 2005 08:31:25 PM PDT