PureInsight | December 3, 2006
In a study previously published in the International Journal of Astrobiology,
researchers state that a meteorite that fell to Earth over northwestern
Canada in January 2000 contains a previously unseen type of primitive
organic material that was formed long before our own solar system came
into being.
The Tagish Lake meteorite fell to Earth over the Yukon Territory of
Canada on Jan. 18, 2000. The Tagish Lake meteorite is a carbonaceous
chondrite, a rare type of meteorite that is rich in organic
(carbon-bearing) compounds. Organic matter in meteorites is a subject
of intense interest because this material formed at the dawn of the
Solar System and may have seeded the early Earth with the building
blocks of life.
The Tagish Lake meteorite is especially valuable for this work because much of
it was collected immediately after its fall over Canada in 2000 and has
been maintained in a frozen state, minimizing terrestrial
contamination. The collection and curation of the meteorite samples
preserved its pristine state.
Through extensive testing using, in part, electron microscopes, the
researchers found numerous hollow, bubble-like hydrocarbon globules in
the meteorite. They believe these organic globules, the first found in
any natural sample, are very similar to those produced in laboratory
simulations designed to recreate the initial conditions present when
life first formed in the universe.
"While not of biological origin themselves, these globules would have
served very well to protect and nurture primitive organisms on Earth,"
said Dr. Michael Zolensky, an author of the paper and a researcher in
the Office of Astromaterials Research and Exploration Science at NASA's
Johnson Space Center in Houston. "They would have been ready-made homes
for early life forms."
The type of meteorite in which the globules were found is also so
fragile that it generally breaks up into dust during its entry into
Earth's atmosphere, scattering its organic contents across a wide swath.
"If, as we suspect, this type of meteorite has been falling onto Earth
throughout its entire history, then the Earth was provided with these
hydrocarbon globules at the same time life was first forming here,"
Zolensky said. "We were exceedingly fortunate that this particular
meteorite was so large that some pieces survived to be recovered on the
ground."
In 2001, researchers at NASA's Ames Research Center in Moffett Field,
Calif., announced that they had made basically identical hydrocarbon
globules in the laboratory from materials present in the early solar
system and interstellar space.
"What we have now shown is that that these globules were in fact made
naturally in the early solar system, and have been falling to Earth
throughout time," Zolensky said. The researchers believe the Tagish
Lake meteorite came from the outer asteroid belt, toward Jupiter, and
that similar organic materials may have been falling onto the moons of
Jupiter, including Europa.
"It is interesting to speculate about the presence of these organics in
the ocean we believe may be present under the ice cap of this moon,"
Zolensky said.
In a paper published in the Dec. 1 issue of the journal Science,
a team headed by NASA space scientist Keiko Nakamura-Messenger, reports
that the Tagish Lake meteorite contains numerous submicrometer hollow
organic globules.
"Similar objects have been reported from several meteorites since the
60's. Some scientists believed these were space organisms, but others
thought they were just terrestrial contamination," said
Nakamura-Messenger. The same bubble-like organic globules appeared in
this freshest meteorite ever received from space. "But in the past,
there was no way to determine for sure where these organic globules
came from because they were simply too small. They are only 1/10,000
inch in size or less."
In 2005, two powerful new nano-technology instruments were installed in
the scientists' laboratory at Johnson Space Center. The organic
globules were first found in ultrathin slices of the meteorite with a
new JEOL transmission electron microscope. It provided detailed
structural and chemical information about the globules. The organic
globules were then analyzed for their isotopic compositions with a new
mass spectrometer, the Cameca NanoSIMS, the first instrument of its
kind capable of making this key measurement on such small objects.
The organic globules in the Tagish Lake meteorites were found to have
very unusual hydrogen and nitrogen isotopic compositions, proving that
the globules did not come from Earth.
"The isotopic ratios in these globules show that they formed at
temperatures of about -260° C, near absolute zero," said Scott
Messenger, NASA space scientist and co-author of the paper. "The
organic globules most likely originated in the cold molecular cloud
that gave birth to our Solar System, or at the outermost reaches of the
early Solar System."
The type of meteorite in which the globules were found is also so
fragile that it generally breaks up into dust during its entry into
Earth's atmosphere, scattering its organic contents across a wide
swath. "If, as we suspect, this type of meteorite has been falling onto
Earth throughout its entire history, then the Earth was seeded with
these organic globules at the same time life was first forming," said
Mike Zolensky, NASA cosmic mineralogist and co-author of the paper.
The origin of life is one of the fundamental unsolved problems in
natural sciences. Some biologists think that making a bubble-shape is
the first step on the path to biotic life. "We may be a step closer to
knowing where our ancestors came from," Nakamura-Messenger said.
References:
http://www.nasa.gov/centers/johnson/news/releases/2002/j02-122.html
http://www.nasa.gov/centers/johnson/news/releases/2006/J06-103.html
