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Fraser
2005-May-05, 04:54 PM
SUMMARY: Geologists have built up a suite of tools and techniques that let them peer back in time to watch the formative stages of the Earth and how it's changed over time - by looking inside rocks. By analyzing trapped water and air in rocks, geologists are studying how our atmosphere changed 3.9 billion years ago, when the crust of the planet was just forming, and there wasn't any oxygen in the air.

View full article (http://www.universetoday.com/am/publish/history_atmosphere_rocks.html)

What do you think about this story? Post your comments below.

om@umr.edu
2005-May-06, 12:13 AM
Looking inside rocks to see the Earth's old atmosphere is an interesting idea.

One of my graduate student, Robert Canalas, analyzed noble gases in the oldest known shale sample in the 1960s to see if we could see evidence for the evolution of Earth's atmosphere.

We didn't find what we expected.

Instead we found that fine grained sediments in shales, young and old, selectively adsorbed large amounts of the heaviest noble gas, xenon, out of air.

That finding offered the first viable explanation for the unusually low Xe/Kr ratio observed in Earth's atmosphere.

The finding may also be used to estimate the amount of sedimentary material on Mars.

If Mars once had oceans and precipitated out sedimentary deposits, then Xe would be selectively adsorbed and the Xe/Kr ratio lowered in the Martian atmosphere. So far as I recall, no depletion of Xe has been observed on Mars.

With kind regards,

Oliver
http://www.umr.edu/~om

JESMKS
2005-May-07, 09:15 PM
There was a report in todays newspaper that analysis of uranium, oxygen and sedimentary materials in inclusions in Zircons from Australia indicates that the Earth had an oxygen atmosphere, and water to produce sedimentary material at a very early age in the earths history. Many millions or years earlier than current estimates.
Jack

om@umr.edu
2005-May-07, 11:01 PM
Hi, Jack.

If you get a reference to that report, please post it.

Are you aware that the high nitrogen/oxygen ratio in air is a major puzzle?

Usually odd-numbered elements, like nitrogen, are less abundant than adjacent even-numbered elements like oxygen.

In stars, meteorites, etc., the N/O ratio is <1. In air the N/O ratio is 4. One way to make such a high ratio is by reacting O with other elements and taking it out of air as a precipitate, e.g., carbonates, rust, etc.

With kind regards,

Oliver
http://www.umr.edu/~om

JESMKS
2005-May-08, 04:40 PM
All I have is the newspaper article. Robert S. Boyd, Knight Ridder Newspapers, It&#39;s headed "Stage set earlier for life on Earth--Land Water, Air detected sooner--Zircon evidence revamps estimates" The article starts"A scientific quest called "Mission to Really Early Earth" has unearthed evidence that our planet had an ocean, a continent and an atmosphere suitable for life 500 million years earlier than previously thought."
It quotes Stephen Mojzsis a geochemist at the University of Colorado.It also quotes statments Bruce Watson, a geochemist at Rensselaer Polytectnic Institute in Troy NY and refers to May 6 weeekly online edition of the journal Science. It also quotes from Mark Harrison, an Australian geoscientist.
The article goes on to state that zircons have been dug up in the Jack Hills in Western Australia and that John Valley a geochemist at the University of Wisconsin has made it possible to determine how and when they formed. For example, zircons contain uranium, which decays to lead at a known rate. The Jack Hills zircons contained bits of shale, a sedimentary rock that must have been created previously by erosion by liquid water. In additio, the zircons contain a rare type of "heavy" oxygen that forms only in the presence of water. The article end with a statement by Sonia Esperanca of the National Science Foundation in Washington DC that the Jack Hills zircons are time capsules of processes happening in the earlist times in Earth&#39;s history.
I hope this helps.
Jack