OFF: Snowball Earth (was The dangers of Cosmic Rock)

[Brian Halligan]

Hi,
I remembered reading a new development in the snowball earth theory, and
after a quick search on ScientificAmerican.com this is what it came up with.

Brian

> New Data Kicks Up 'Snowball Earth' Fight
> Dec. 5, 2001
>
> In 1998, Paul F. Hoffman and Daniel P. Schrag at Harvard University put forth
> a chilling description of earth's climate some 650 million years ago. Their
> theory, dubbed snowball earth, held that between 750 million and 580 million
> years ago, ice repeatedly enveloped our planet, coating the seas from pole to
> pole and killing off early life almost completely. During the past few years,
> the idea has stirred up a great deal of debate. And new data published in the
> December issue of Geology only further throws snowball earth into question.
>
> Lead author Martin Kennedy at the University of California, Riverside, and
> colleagues collected limestone and dolomite rocks from Precambrain glacial
> deposits in northern Namibia, central Australia and the North American
> Cordillera. When they analyzed these samples, they discovered that the ratio
> of the carbon isotope 13C to 12C was higher during the glaciation than after
> the ice had melted. This pattern, they say, suggests that the oceans supported
> a healthy ecosystem at the time‹which would be hard to do were they frozen
> over.
>
> "If there was no photosynthesis or life in the ocean, the carbon isotope
> values would be the same as the mantle," Kennedy says. "Only the presence of
> life causes a difference in those values. We did not find isotopic evidence
> that a global ice sheet impacted overall marine productivity. We would think
> that if an ice sheet covered the oceans it would have had an impact on marine
> production or photosynthesis and we find no carbon isotopic evidence for this.
> The oceans just look normal."‹Kristin Leutwyler