Re: How Long has Earth been habitable?

Mike Dworetsky <platinum198@[EMAIL PROTECTED]
>:
>  I'm told (via some googling at a few sites) that the best estimates are
that 
>  the atmosphere reached O2 levels similar to today around 400 MY ago. 
It 
>  seems doubtful that humans could have survived during the late
Cambrian, 
>  around 530 MY ago.  There was some oxygen but probably not enough (a
few %). 
>  I don't think the high levels ever disappeared or reduced to below 
>  land-animal survivability once they appeared.

Also, tghe ozone kayer only formed around then, adn with no ozone you
don't really want to walk around on th surface.

/Par


-- 
Par              	                          usenet@[EMAIL PROTECTED]
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