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

[j.divelbiss 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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