Note: The following article was published in late August in the New York Times. It's highly interesting because it runs on two parallel levels, i.e., as a "straight" account of an important scientific discovery and also as a tale of professional jealousy. I've tried to demarcate the two levels by assigning them different color type here, but basically it's a story worth reading and information worth knowing.
A
collection of tubular microfossils found in 3.4-billion-year-old sandstone from
Western Australia (photograph: David Wacey)
By:
NICHOLAS WADE
A team of Australian and British
geologists have discovered fossilized, single-cell organisms that are 3.4
billion years old and that the scientists say are the oldest known fossils on
earth.
Their assertion, if sustained,
confirms the view that life evolved on earth surprisingly soon after the Late Heavy Bombardment, a reign of destruction in which waves of asteroids slammed
into the primitive planet, heating the surface to molten rock and boiling the
oceans into an incandescent mist. The bombardment, which ended around 3.85
billion years ago, would have sterilized the earth’s surface of any incipient
life.
The claim is also a new volley in a
long-running conflict over who has found the oldest fossil.
The new microfossils are described
in Sunday’s issue of Nature Geoscience by a team led by David Wacey of the
University of Western Australia and Martin D. Brasier of the University of Oxford. The fossils were found in sandstone at the base of the
Strelley Pool rock formation in Western Australia.
The sandstone, 3.4 billion years
ago, was a beach on one of the few islands that had started to appear above the
ocean’s surface. Conditions were very different from those of today. The moon
orbited far closer to earth, raising huge tides. The atmosphere was full of
methane, since plants had not yet evolved to provide oxygen, and greenhouse
warming from the methane had heated the oceans to the temperature of a hot
bath.
It was in these conditions, the
geologists believe, that organisms resembling today’s bacteria lived in the
crevices between the pebbles on the beach. Examining thin slices of rock under
the microscope, they have found structures that look like living cells, some in
clusters that seem to show cell division.
Cell-like structures in ancient
rocks can be deceiving — many have turned out to be artifacts formed by
nonbiological processes. In this case, the geologists have gathered
considerable circumstantial evidence that the structures they see are
biological. With an advanced new technique, they have analyzed the composition
of very small spots within the cell-like structures. “We can see carbon,
sulfur, nitrogen and phosphorus, all within the cell walls,” Dr. Brasier said.
Crystals of fool’s gold, an
iron-sulfur mineral, lie next to the microfossils and indicate that the
organisms, in the absence of oxygen, fed off sulfur compounds, Dr. Brasier and
his colleagues say.
Microfossils — the cell-like structures
found in ancient rocks — have become a highly contentious field, both because
of the pitfalls in proving that they are truly biological and because the
scientific glory of having found the oldest known fossil has led to pitched
battles between rival claimants.
Microfossils
discovered in Western Australia by J. William Schopf, University of
California, Los Angeles. A photograph of each specimen appears with an
interpretive drawing of the structure. (Photograph courtesy of J.
William Schopf).
The honor of having found the most
ancient microfossil has been long been held by J. W. Schopf, a paleobiologist
at the University of California, Los Angeles. In 1993, Dr. Schopf reported his discovery of fossils 3.465 billion years
old in the Apex chert of the Warrawoona
Group in Western Australia, about 20 miles from where the new fossils have been
found. Those would be some 65 million years older than the new find, but Dr.
Schopf’s claim was thrown in doubt in 2002 when Dr. Brasier attacked
his finding, saying the fossils were not
biological but just mineral artifacts.
With the new discovery, Dr. Brasier
has dropped the second shoe, claiming to find microfossils that are or may be
the oldest known, if and when Dr. Schopf’s are knocked out of the running.
The Nature Geoscience article
published on Sunday does not claim discovery of the earth’s oldest
microfossils. That assertion was made in a press release issued by the
University of Oxford, where Dr. Brasier is a professor in the department of
earth sciences.
Dr. Brasier said the article
submitted to Nature Geoscience had made such a claim, but the reviewers
questioned the advisability of doing so, and the senior author, Dr. Wacey,
“decided to acquiesce on this particular point.”
Dr. Schopf did not respond to an
e-mail seeking his comments. “Bill Schopf still very strongly defends his
original claim, and is working to validate it,” said Roger Buick, an earth
scientist at the University of Washington.
Dr. Buick said there was no
consensus on Dr. Schopf’s microfossils, but that “the majority opinion is that they are probably not biological and probably not as old as claimed.”
The team led by Dr. Wacey and Dr.
Brasier has made a “pretty good case,” Dr. Buick said, because the many
different analytic techniques they have used “lend credence to the argument in
a way that many other previously reported discoveries of particularly ancient
microfossils have not.”
Does that mean the new microfossils
are the oldest known? “If these are valid, and if we discount the Schopf
microfossils, these would be the oldest known, though not by much,” Dr. Buick
said.
Artist's rendering of Earth during the Archean eon, i.e., 2.5 billion years ago. (Peter Sawyer, Smithsonian Institution).
Rocks older than 3.5 billion years
have been so thoroughly cooked as to destroy all cellular structures, but
chemical traces of life can still be detected. Chemicals indicative of life
have been reported in rocks 3.5 billion years old in the Dresser Formation of
Western Australia and, with less certainty, in rocks 3.8 billion years old in
Greenland.
“This struggle to be the owner of
the world’s oldest microfossils is really not the crux of the battle for
understanding the early development of life anymore,” Dr. Buick said.
Andrew H. Knoll, an earth
scientist at Harvard, said in a brief e-mail from a Moscow airport that the
researchers had not proved their point that the fossils, when alive, fed on
sulfur compounds. But he did not take sides on the dispute between Dr. Brasier
and Dr. Schopf.
Dr. Buick said: “You’ve got to
realize how divisive this microfossil war has been over the last decade. Most
people just want it to be over. If claim and counterclaim go back and forth for
a decade, it sounds like we don’t know what we’re doing.”
Ship's chronometer used on HMS Beagle during Charles Darwin's 1831 - 1836 voyage. This instrument was made by Thomas Earnshaw (1749-1828) and is on permanent display in Rooms 38-39 (Clocks and Watches) of the British Museum, London.
