News: Looking for signs of early life
- From: "Robert Karl Stonjek" <rstonjek@xxxxxxxxxxxxxx>
- Date: Fri, 10 Jul 2009 13:11:36 -0400 (EDT)
Looking for signs of early life
(PhysOrg.com) -- Deciphering the very early history of life on Earth is
difficult. In the darkest recesses of the first billion years there are no
'body' fossils - no physical remains. Instead, scientists use chemical
signals left behind in the rock record.
Methanogens are single cell microorganisms that make their energy by
converting either simple organic compounds or carbon dioxide and hydrogen to
methane. Nickel, an important nutrient for these organisms, may be a useful
chemical signal to pinpoint the early origins of life on Earth, according to
researchers at the University of Bristol, UK, and Penn State University, US.
Dr Vyllinniskii Cameron, lead author on the paper published recently in
PNAS, said: "Life has had a profound chemical impact on our planet - the
most spectacular effect being the high oxygen content of our atmosphere,
which is a result of photosynthesizing algae, plants and some bacteria
producing oxygen as a waste product.
"But photosynthesis as a means of producing energy for life is a relatively
new kid on the block in terms of evolution, probably originating no more
than about 2-2.5 billion years ago. Before that, other life modes such as
methanogens dominated."
Methanogens and their metabolisms are probably key to development of the
early Earth. Not only are they one of the most primitive organisms on Earth,
but their waste product - methane - may have been the dominant greenhouse
gas on the early planet. Many scientists believe that it was methane that
made early temperatures on Earth equable, despite the fact that the Sun was
about 30% weaker in the early stages of the Solar System.
A chemical marker for methanogens in rocks is therefore to be greatly sought
after. Cameron and colleagues suggest that the isotopes of nickel may
represent such a marker.
Fractionation of an element into its component stable isotopes occurs
because each isotope is slightly different in mass. Biological organisms
tend to favour one isotope over another and preferentially create stores of
heavy or light isotopes that researchers can measure. The presence of a
specific isotopic fraction can indicate that a biological process took
place. Previous researchers have looked at transition metals other than
nickel as potential biomarkers.
For this work the researchers did not look at ancient fossil cells, but grew
modern day methanogens in the laboratory, controlling their habitat and
recording their rate of methane production. They showed that these microbes
take up the isotopes of nickel in a very specific way, suggesting that a
search for this distinctive nickel (bio)signature might serve as a marker
for the existence of methanogens on the early Earth - and, perhaps, on other
planets.
More information: A biomarker based on the stable isotopes of nickel by
Vyllinniskii Cameron, Derek Vance, Corey Archer and Christopher H. House.
PNAS, July 7, 2009.
http://www.pnas.org/content/early/2009/06/23/0900726106.abstract
Provided by University of Bristol (news : web)
http://www.physorg.com/news166284392.html
Posted by
Robert Karl Stonjek
.
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