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Re: Mystery of Mass Extinctions Is No Longer Murky

A moist greenhouse (or wet greenhouse) is inevitable because the sun is 
gradually warming as it burns hydrogen, but calculations I saw predicted that 
it would take 1.1 billion years, at which point the sun would be 11% brighter. 
The theory is that the oceans will gradually evaporate, and water vapor will 
rise into the stratosphere, where solar ultraviolet will split the water 
molecules into hydrogen and oxygen and the oxygen will escape. 

Any proper model of climate in deep geologic time has to consider the lower 
solar flux earlier in the Earth's history. It's only a few percent back in the 
Cretaecous, but becomes more significant earlier. 

At 6:22 PM +1000 7/6/08, Adam wrote:
>Hi Guys
>Having studied atmospheres a bit I concur - Earth can't get so hot that it 
>wouldn't rain anymore. I'm not entirely sure the Earth would even be 
>dehydrated the same way Venus is supposed to have lost its ocean. Hydrodynamic 
>outflow of gases from Venus' exosphere in the early days of the Solar System 
>was driven partly by the much higher UV put out by the early Sun.
>However a "wet Greenhouse" is hotter than a high-pressure autoclave, even if 
>the oceans are still around - with about 10 bars worth in the atmosphere. 
>Could Earth be tipped towards that end-state? We really don't know, but the 
>end of the Cryogenian glaciations via a massive greenhouse was the worst seen 
>since the hot times of the Archean - and the Earth didn't tip then. Would our 
>little perturbation really be enough to push the Earth's systems past that 
>point? Maybe not, but it could end up with 50 C temperatures in the Caribbean 
>like during the Cretaceous...
Jeff Hecht, science & technology writer
jeff@jeffhecht.com  http://www.jeffhecht.com
Boston Correspondent: New Scientist magazine
525 Auburn St., Auburndale, MA 02466 USA
tel. 617-965-3834