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Fraser
2005-Apr-21, 04:41 PM
SUMMARY: The planets in our Solar System formed more than 4.6 billion years ago from cloud of dust and gas that collapsed under gravity. Scientists have speculated that this cloud lasted anywhere from 1 to 10 million years, but new research has pegged that period at 2 million years. An international team of researchers studied a variety of meteorites that had formed just before the planets. One group, called calcium aluminum-rich inclusions are known to have formed early in the solar nebula, and others, called chondrules, formed right at the end - 2 million years later.


View full article (http://www.universetoday.com/am/publish/solar_nebula_2_million.html)

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GOURDHEAD
2005-Apr-21, 04:55 PM
From the article:
CAIs were formed in an oxygen-rich environment and date to 4.567 billion years old, while chondrules were formed in an oxygen setting much like that on Earth and date to 4.565 billion, or less, years old. How were the time intervals calculated? I'm astonished that we are that good at dating events that far back.

om@umr.edu
2005-Apr-21, 05:48 PM
You're right, Gourdhead. They do not explain how they obtained an age difference of 0.002 billion years.

It is probably based on dating with a short-lived isotope - probably something like Al-26 - present when fresh, poorly-mixed supoernova debris started to form the solar system.

The report raises many questions. Confusion may come from

a.) a recent report in Nature that the Sun itself contains at least 2% more O-16 than the Earth, and

b.) an older report that the amounts of some short-lived isotopes varied with helio-centric distance.

The lead author is a well-respected scientist. However, he still seems to imagine one interstellar cloud forming the solar system while another mysterious source injected mono-isotopic O-16:

“Over this span of about two million years, the oxygen in the solar nebula changed substantially in its isotopic makeup,” Hutcheon said. “This is telling us that oxygen was evolving fairly rapidly.”

“By the time chondrules formed, the O-16 content changed to resemble what we have on Earth today,” Hutcheon said.

With kind regards,

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