[meteorite-list] Helium Helps Trace the Origin of the Los AngelesMeteorite

From: j.divelbiss_at_att.net <j.divelbiss_at_meteoritecentral.com>
Date: Thu Oct 28 15:15:33 2004
Message-ID: <102820041915.16221.41814551000E3CED00003F5D21602813029C9C070D040A90070BD206_at_att.net>

"It makes meeeeee sound like thiiiisss, as long as I hold my breath while tallllkingggggg"...said the helium inhaling squealing clown of a meteorite scientist. Helium can be fun too !

JD


 
-------------- Original message from "Matt Morgan" <mmorgan_at_mhmeteorites.com>: --------------


> This is interesting. How far back can we use Helium before it completely
> decays?
> Matt
> <><><><><><><>
> Matt Morgan
> Mile High Meteorites
> http://www.mhmeteorites.com
> PO Box 151293
> Lakewood, CO 80215 USA
> ebay id: mhmeteorites
> ----- Original Message -----
> From: "Ron Baalke"
> To: "Meteorite Mailing List"
> Sent: Thursday, October 28, 2004 10:51 AM
> Subject: [meteorite-list] Helium Helps Trace the Origin of the Los
> AngelesMeteorite
>
>
> >
> >
> > http://www.yaledailynews.com/article.asp?AID=27007
> >
> > Helium helps trace the origin of Martian meteorite
> > BY ASHLEY FOX
> > Yale Daily News
> > October 28, 2004
> >
> > While cleaning out his rock collection in 1999, Los Angeles resident and
> > rock-enthusiast Bob Verish came across two unusual looking stones he had
> > picked up on a hike in the Mojave Desert 20 years earlier. The stones,
> > which Verish named "Miguel" and "Gabriel," were soon recognized by UCLA
> > scientists as remnants of a meteorite from Mars.
> >
> > Four researchers from Yale's Geology and Geophysics Department, led by
> > post-doctoral fellow Kyoungwon Kyle Min, have taken up the quest to
> > uncover the story behind these unlikely space travelers, a story that
> > began around three million years ago.
> >
> > "We wanted to know the time-temperature history of meteorites, not just
> > when they were formed," said Peter Reiners, a member of the Yale team
> > and a professor of geology and geophysics. "This tells us about their
> > history in space and on other planets. We want to know how often things
> > bump into each other and how hard."
> >
> > In order to draw such conclusions about the Martian meteorite, now
> > referred to as the "Los Angeles" or "LA," the team had to think outside
> > the box -- or, in this case, outside the planet. They identified a
> > method of helium dating which is used on terrestrial rocks and applied
> > it to the meteorite from Mars, Reiners said.
> >
> > The team knew that a meteor had hit Mars prior to the time that the LA
> > was ejected from the red planet, Min said. When this meteor hit Mars, it
> > caused a change in the constitution of the rock on the planet, known as
> > impact-related shock metamorphism. The team was fortunate that the
> > interior of the LA meteorite preserved its original Martian signatures,
> > including those from the original Martian impact, making the LA a
> > virtual time capsule from the impact of the meteorite on Mars, Min said.
> >
> > During the impact, helium atoms, products of spontaneous uranium and
> > thorium decay, would have been completely diffused out of the rock,
> > Reiners said. As a result, the team, which also included Yale
> > researchers Stefan Nicolescu and James Greenwood, was able to determine
> > when the meteorite hit Mars by measuring the uranium, thorium and helium
> > content of the sample.
> >
> > Min said the study was innovative in its use of helium measurements from
> > only single grains of the meteorite. By employing this method, Min and
> > his colleagues discovered that the impact occurred on Mars around three
> > million years ago. They were also able to conclude that the maximum
> > temperature of impact was between 450 and 500 degrees Celsius, Reiners
> said.
> >
> > The helium age was then compared to the LA's exposure age, the amount of
> > time that the sample has been exposed to cosmic rays. Since the LA was
> > underground until its ejection from Mars, the exposure age equals the
> > amount of time since it left Mars, Min said. The exposure age was also
> > found to be about three million years. He said a main conclusion of the
> > study was the similarity of the helium and exposure ages.
> >
> > "Thus, we showed that the impact that launched it [the LA] off the
> > planet also heated it up to pretty high temperatures," Reiners said.
> >
> > According to the study, this new method of meteorite analysis allows
> > scientists to better understand the time and temperature impact
> > processes. The method has a variety of applications to terrestrial and
> > extraterrestrial materials, higher thermal sensitivity than other
> > techniques and an accessible age range that spans from the birth of the
> > solar system to the beginning of modern human history, according to the
> > study.
> >
> > Although Min's technique cannot directly answer the question of
> > extraterrestrial life, it could aid scientists in this search.
> >
> > "It could tell us about how material that could potentially contain
> > traces of life from Mars could or could not be transported to earth,"
> > Reiners said.
> >
> > By accurately determining the temperature, pressure and time of shock
> > metamorphism, scientists can gauge the probability of finding evidence
> > of life in meteorites, Min said.
> >
> >
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Received on Thu 28 Oct 2004 03:15:30 PM PDT