[meteorite-list] Meteorites Could Have Thickened Primordial Soup

From: Ron Baalke <baalke_at_meteoritecentral.com>
Date: Mon, 8 Dec 2008 13:51:57 -0800 (PST)
Message-ID: <200812082151.NAA27936_at_zagami.jpl.nasa.gov>

http://www.sciencenews.org/view/generic/id/39124/title/Meteorites_could

Meteorites could have thickened primordial soup

High temperatures and pressures of impacts can create complex organic
chemicals, tests show

By Sid Perkins
Science News
December 8, 2008

In recent geological ages, large extraterrestrial bodies colliding with
Earth have been associated with worldwide extinctions, but new
experiments show that massive impacts that occurred early in our
planet's history could have created the raw materials for life.

The hellish temperatures and pressures generated when an
extraterrestrial object strikes Earth at speeds of several kilometers
per second are enough to shatter and vaporize rock (SN: 6/15/02, p.
378). Yet part of such an immense burst of energy can trigger chemical
reactions that generate complex organic substances from basic inorganic
ingredients, says Takeshi Kakegawa, a geochemist at Tohoku University in
Sendai, Japan. He and his colleagues conducted lab experiments intended
to simulate a common meteorite striking one of Earth's early oceans. The
team reports its findings online December 7 in Nature Geoscience.

First, the researchers filled tiny, thick-walled canisters of stainless
steel with various mixtures of carbon, iron and nickel - common
constituents of meteorites - and water, ammonia and nitrogen, significant
components of the ancient ocean and atmosphere. Then, the team fired the
canisters at a solid target. The shock of impact briefly subjected the
enclosed materials to temperatures approaching 4,700?? Celsius and
pressures about 60,000 times that of the atmosphere at sea level. These
temperature and pressures are similar to those that would be caused by a
large meteorite slamming into Earth at about 2 kilometers per second,
says Kakegawa.

After each test, Kakegawa and his team cleaned off the outside of the
canister, drilled a hole in it, and then extracted and analyzed the
contents. In two of the team's five tests, impacts created fatty acids
like those found in cell membranes, and also generated a variety of
amines, the ingredients for amino acids, Kakegawa says. In one test, the
impact generated substantial amounts of glycine, the smallest of the 20
amino acids commonly found in proteins.

None of the organic chemicals generated by the impacts was a contaminant
from any poor handling, Kakegawa proposes. That's because all of the
carbon in those resulting substances was the carbon-13 isotope, the same
rare form that he and his colleagues used for the original mixture.

Scientists estimate that around 4 billion billion (1018) metric tons of
meteorites fell to Earth between 4.4 billion and 3.8 billion years ago.
Even though meteorites only contain, on average, about 0.1 percent
carbon, oceanic impacts during this era could have generated at least
one hundred billion (1011) metric tons of organic substances, the
researchers estimate. Although these chemicals couldn't have survived
the conditions at ground zero of the impact, they probably could have
formed in the more-tolerable temperatures present in the plumes of steam
and vaporized rock that spewed skyward in the aftermath.

The team's new analyses "are a nice piece of work," says George Cody, a
geoscientist at the Carnegie Institution for Science in Washington, D.C.
A number of previous studies have hinted that the building blocks of
life could have been generated by lightning in Earth's ancient
atmosphere (SN: 6/3/00, p. 363) or at deep-sea hydrothermal vents (SN:
9/9/00, p. 175; SN: 2/2/08, p. 67). Having multiple sources of such raw
materials "makes determining the origin of life that much more
difficult," Cody adds. However, he notes, "the more we learn, the more
we see how early Earth was rich with organic compounds."
Received on Mon 08 Dec 2008 04:51:57 PM PST