Primordial Air Mau Have Been Breathable

[Richard W Travsky <rtravsky@uwyo.edu>]

For those interested in a slightly older phase of the Earth:

http://www.csiro.au/index.asp?type=mediaRelease&id=Prpisoliths

The Earth may have had an oxygen-rich atmosphere as long ago as three
billion years and possibly even earlier, three leading geologists have
claimed.

Their theory challenges long-held ideas about when the Earth's atmosphere
became enriched with oxygen, and pushes the likely date for formation of
an atmosphere resembling today's far back into the early history of the
planet.
...
The researchers' theory has been lent additional weight by evidence from
the Western Australian Pilbara region for the presence of sulphates in
rocks up to 3.5 billion years old.  These, too, could not have formed
without an oxygen-rich atmosphere.