Bert,
"Complex life" in this instance means "eukaryotes". It
doesn't mean multicellular forms (well, some bacteria have
multicellular forms too), plants or metazoans. The evidence
is based on detecting sterols, which is taken to be indicative
of eukaryotic life. There is no information about the structure
of the cells which may have produced these sterols. Thus it
is unknown whether these sterol-containing organisms had a
nucleus, mitochondria, or chloroplasts: eg. structural features
with which we identify eukaryotes of today.
Even so, and if this report is true, there are still between one
or two billion years separating the first appearance of life
(bacterial) and the first evidence of eukaryotic life. If
anything, it extends the "calendar time for gradualistic
development" of subsequent eukaryotic life (leading to
multicellular forms).
James Mahaffy mentioned that he would like to see the
results corroborated with fossil evidence. There is one
problem with this. It's not clear that an early eukaryote
would look all that different from a bacterium. Previously,
size differences were thought to be sufficient for
distinguishing between the two, but we've since found bacteria
that are as large (or larger) than some eukaryotic organisms.
There may be some microfossils which are clearly eukaryotic,
but there will always be a grey zone for others.
Regards,
Tim Ikeda
tikeda@sprintmail.hormel.com
(despam address before use)