Subject: oldest eukaryotes? (off topic)
Date: Aug 16 10:54:50 1999
From: Dale Goble - gobled at uidaho.edu




On Mon, 16 Aug 1999 tuisto at oz.net wrote:

> that are more than 1.7 billion years old. Did anyone notice this news story
> go by?


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.
The life forms are single-celled creatures called eukaryotes, the
first known cells to have nuclei and specialized internal strcutures for
processing energy. Present-day descendants of this group include all the
higher kingdoms of life, like plants, animals, fungi, as well as
sinble-celled creatures like amoebae.
The first life, simple bacteria with no nuclei, is believed on th
ebasis of fossils to have appeared by 3.5 billion years ago and possibly
3.8 billion years ago. The earth is about 4.6 billion years old.
The new findings, reported in todyas issue of the journal Science,
are based on fatty molecules known to be produced by living cells that
were found in ancient shale in northwestern Australia by a team lead by
Jochen J. Brocks, a geoscientist at the University of Sydney. The
chemicals, called sterols, are found in the membranes of eukaryotes.
Although it is possible that simpler organisms produced the
sterols, the Australian researchers wrote in Science, the abundance of
this class of chemicals "is convincing evidence for the presence of
eukaryotes" aroun 2.7 billion years ago.
Other scientists noted that it was not known whether the cells
that produced the fatty moleculrs had yet developed the other
characteristis of eukaryotes. These includes structures call
chloroplasts, which enable plants to draw energy from the sun through
photosynthesis, and mitchonsria, which enable plant and animal cells to
process energy.
"All we can say is that one important attribute of eukaryotes was
in place" by 2.7 billion years ago, Andrew H. Knoll, a paleontologist at
the Harvard University Botanical Museum, said in an interview.
Nevertheless, Dr. Knoll wrote in a commentary in Science, the
fiding highlights two points. First, there was a very long interval --
1.5 billion years or more, if eukaryotes did arise as long ago as the new
study suggests -- between their first appearance and the beginning of
their flowering into higher organisms 1.2 billion to 1 billion years ago.
Second, the findings push back still farther the frontier of
investigation of early life. For generations, Dr. Knoll wrote, an
explosion of higher forms of life about 544 million years ago, at the
beginning of the Cambrian period, marked a terra incognita beyond which
little or nothing was known about life. This "line of paleontological
frustration," as he called it, lated receded to 2 billion years ago, and
had now receded even further.
The Brocks findings, Dr. Knoll, wrote, dramatically lenghten "both
the geological record of eukaryotic biology and the list of questions we
need to ask about early evolution."

[the typos are mine alone]

Dale Goble
Moscow