In article <1ib6f9k.4s93omih5yugN%herwin@[EMAIL PROTECTED]
>,
Harry Erwin <herwin@[EMAIL PROTECTED]
> wrote:
>Paul Ciszek <nospam@[EMAIL PROTECTED]
> wrote:
>
>> When did Earth first have an atmosphere with enough O2 and a low enough
>> CO2 level that an unprotected human could breathe? Have there been any
>> times since then that these conditons were not met?
>
>They don't really know.
>
>On the other hand, agriculture seems to have been infeasible during
>glacial periods--the climate was too chaotic--so you might find that
>there were other factors that would rule out settlement.
Basically, I am looking for a snappy comeback when climate change
skeptics say, "Oh, the Earth's climate and CO2 level have changed
a lot more than this." I want to be able to say something like,
"Yes, there have been times when you couldn't even breathe. Are
you sure that helps your argument?" Although, not being about to
practice agriculture is a good point too. Do you know, by any chance,
if gr***** suffered during the Eocene thermal maximum? I like to
use that as an example of what could happen if there is a sudden
(by geological standards) release of a lot of CO2.
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