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Published: 10 hours ago, 14:21 EST, March 26, 2008
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Scientists discover clue to 2 billion year delay of life on Earth
Earth Scientists from around the world have reconstructed changes in
Earth’s ancient ocean chemistry during a broad sweep of geological time,
from about 2.5 to 0.5 billion years ago. They have discovered that a
deficiency of oxygen and the heavy metal molybdenum in the ancient deep
ocean may have delayed the evolution of animal life on Earth for nearly 2
billion years.
The findings, which appear in the March 27 issue of /Nature/, come as no
surprise to Ariel Anbar, one of the authors of the study and an associate
professor at Arizona State University with joint appointments in the
Department of Chemistry and Biochemistry and the School of Earth and Space
Exploration in the College of Liberal Arts and Sciences.
The study was led by Clint Scott, a graduate student at University of
California Riverside. Scott works with Timothy Lyons, a professor of
biogeochemistry at UCR who is a long-time collaborator of Anbar’s and also
an author of the paper.
“Clint’s data are an important new piece in a puzzle we’ve been trying to
solve for many years,” says Anbar. “Tim and I have suspected for a while
that if the oceans at that time were oxygen deficient they should also
have been deficient in molybdenum. We’ve found evidence of that deficiency
before, at a couple of particular points in time. The new data are
important because they confirm that those points were typical for their
era.”
Molybdenum is of interest to Anbar and others because it is used by some
bacteria to convert the element nitrogen from a gas in the atmosphere to a
form useful for living things – a process known as “nitrogen fixation.”
Bacteria cannot fix nitrogen efficiently when they are deprived of
molybdenum. And if bacteria can’t fix nitrogen fast enough then eukaryotes
– a kind of organism that includes plants, pachyderms and people – are in
trouble because eukaryotes cannot fix nitrogen themselves at all.
“If molybdenum was scarce, bacteria would have had the upper hand,”
continues Anbar. “Eukaryotes depend on bacteria having an easy enough time
fixing nitrogen that there’s enough to go around. So if bacteria were
struggling to get enough molybdenum, there probably wouldn’t have been
enough fixed nitrogen for eukaryotes to flourish.”
“These molybdenum depletions may have retarded the development of complex
life such as animals for almost two billion years of Earth history,” says
Lyons. “The amount of molybdenum in the ocean probably played a major role
in the development of early life.”
This research was motivated by a review article published in Science in
2002 by Anbar and Andy Knoll, a colleague at Harvard University. Knoll was
perplexed by the fact that eukaryotes didn’t dominate the world until
around 0.7 billion years ago, even though they seemed to have evolved
before 2.7 billion years ago. Together, Anbar and Knoll postulated that
molybdenum deficiency was the key, arguing that the metal should have been
scarce in ancient oceans because there was so little oxygen in the
atmosphere in those times.
In today’s high-oxygen world, molybdenum is the most abundant transition
metal in the oceans. That is because the primary source of molybdenum to
the ocean is the reaction of oxygen with molybdenum-bearing minerals in
rocks. So the hypotheses rode on the idea that the amount of molybdenum in
the oceans should track the amount of oxygen.
To test that idea, Scott, Lyons and Anbar examined rock samples from
ancient seafloors by dissolving them in a cocktail of acids and analyzing
the rock for molybdenum content using a mass spectrometer. Many of these
analyses were carried out using state-of-the art instrumentation in the W.
M. Keck Foundation Laboratory for Environmental Biogeochemistry at Arizona
State University. The scientists found significant evidence for a
molybdenum-depleted ocean relative to the high levels measured in modern,
oxygen-rich seawater.
By studying Earth’s ancient oceans, atmosphere and biology we can test how
well we understand the modern environment, according to Anbar. “Our
molybdenum hypothesis was inspired by the theory that biology in the
oceans today is often starved for a different metal – iron – and that the
lack of iron in parts of the oceans affects the transfer of the greenhouse
gas carbon dioxide from the atmosphere to the ocean” he says. “The idea
that metal deficiency in the oceans can affect the entire planet is very
powerful. Here, we are exploring the limits of that idea by seeing if it
can solve ancient puzzles. These new findings strengthen our confidence
that it can.”
Source: Arizona State University
Posted by Modernmystic 8 hours ago
Not rated yet.
I wonder how this will effect "Rare Earth" supporters ideas.
Posted by dedereu 4 hours ago
Not rated yet.
extremely important proof and discovery showing that all lifes are
linked on our earth Gaia.
Iron from inside earth to remove CO2, photosynthesis to obtain O2, which
is supressed by oxydizing Fe during more than 1 billion years up to when
the rate of Fe from inside earth decreases allowing a large increases in
O2, allowing use of molybdenum for multicellular life