At 10:54 AM 8/16/99 -0700, Dale Goble wrote:

>An article appeared in the New York Times on Friday, August 13:
>
> Date for First Complex Life Is Pushed Back
> by William K. Stevens

> Australian scientists say they have found evidence that complex
>forms of life existed on the earth 2.7 billion years ago, 500 million to 1
>billion years earlier than previously thought.

Thanks to Dale and others for replying to my off-topic question. I
realized after I sent my query this morning that I had heard the tail-end
of a report on molecular fossils on the radio last week, but not enough to
get the picture. Today my issue of Science arrived in my mailbox with the
full story.
Molecular fossils (steranes) indicative of eukaryotic (nucleated) cells
were found in 2.7 billion-year-old shales from the Pilbara Craton in
Australia, along with 2a-methylhopanes, which are indicative of
cyanobacteria (formerly known as blue-green algae), the friendly little
photosynthesizers that brought us oxygen in the atmosphere and gave rise to
chloroplasts, permitting photosynthesis in eukaryotic algae and plants. The
molecular fossils are indeed a billion years older than the next oldest
similar sterane fossils, and half a billion years older than Grypania, the
oldest eukaryotic cellular fossils (from Michigan). Eukaryotes have often
been thought to have originated relatively recently (< 1 billion years
ago), although an alternative view, supported by the present results, is
that they are much older. Cyanobacteria, on the other hand, may be more
than 3.5 billion years old, based on cellular fossils of probable
cyanobacteria from western Australia and isotopic evidence of
photosynthesis from Greenland.

Paul Talbert
Seattle
tuisto at oz.net