New Analysis of Meteorite Shows Key Ingredients for Life on Earth May Have Been Delivered by Comets

An object that fell to Earth more than 136 years ago has revealed new
clues about the origin of meteorites in space and new information about
how life may have started on early Earth. The new study by researchers
at Scripps Institution of Oceanography at the University of California,
San Diego, and their colleagues shows that the Orgueil meteorite, which
fell in France in 1864, may be the first meteorite traced to a comet,
rather than from an asteroid, the source widely believed to produce
meteorites.

The contents within Orgueil, the study says, may have been just the type
of fundamental ingredients necessary to help generate life on Earth.
Scientists have generally believed that a wide variety of amino acids
were required for the origin of life on Earth.

“Recent research suggests, however, that only a few types of simple amino
acids may have been required, and that is exactly what we have found
to be present in Orgueil,” said Jeffrey Bada, a professor of marine
chemistry at Scripps.

The study appears in the Feb. 27 issue of the Proceedings of the National
Academy of Sciences and is authored by Bada, Daniel Glavin, and Oliver
Botta of Scripps; Pascale Ehrenfreund of the Leiden Observatory in the
Netherlands; and George Cooper of the NASA Ames Research Center.

Although the Orgueil meteorite, named after the French town near where
it fell in 1864, had been analyzed decades ago, Bada and his colleagues
conducted a new study using sophisticated techniques and instruments
aimed at detecting trace levels of amino acids. Amino acids are the
fundamental components of proteins and are synthesized in living cells.

After obtaining a pristine piece of the interior portion of Orgueil, the
researchers found that it contained a relatively simple mixture of amino
acids, consisting primarily of glycine and beta-alanine. They also
analyzed the sample’s carbon isotope concentration and found that the
amino acids were not derived from earthly contamination.

“We found that the amino acids in Orgueil are abiotic. They were formed
without the help of biology, only chemical reactions,” said co-author
Botta. “We think these amino acids were synthesized in space.”

The research team then compared their results with three other
meteorites: Murchison and Murray, which have been studied extensively,
and Ivuna, a meteorite that fell in Tanzania, Africa, in 1938 that had
not been analyzed for amino acids.

The research team broke the meteorites down into two classes. The
Murchison and Murray meteorites were placed in a category containing a
complex mix of amino acids made up of more than 70 different types of
amino acids. Orgueil and Ivuna, however, were categorized with a much
simpler composition made up primarily of just two amino acids.

Based on the unique amino acid composition within Orgueil, the
researchers were able to deduce information about the meteorite’s past.
Murchison and Murray are widely believed to be pieces of an asteroid,
as are virtually all meteorites scientists have studied. However the
paper suggests Orgueil and Ivuna show evidence that they are likely
derived from a comet. The amino acid signatures within Orgueil and
Ivuna suggest that these compounds were likely synthesized from
components such as hydrogen cyanide, which have been recently observed
in the comets Hale-Bopp and Hyakutake.

“This suggested to us that what we may be seeing in Orgueil and Ivuna
are the products of reactions that once took place in the nucleus of
a comet,” said Bada.

“If it’s true, this would be the first time that a meteorite from the
nucleus of a comet has been identified,” said co-author Glavin. “There
is really a lot we don’t understand about the chemistry of a comet
nucleus and this would be our first insight.”

Thus, the paper suggests, the amino acids that helped generate life on
Earth may have been delivered by meteorites that were derived from the
remnants of comets.

The study was funded by the National Aeronautics and Space Administration
Specialized Center of Research and Training in Exobiology at Scripps, the
Austrian Academy of Sciences, and the Netherlands Research School for
Astronomy.

Scripps Institution of Oceanography, at the University of California, San
Diego, is one of the oldest, largest, and most important centers for global
science research and graduate training in the world. The National Research
Council has ranked Scripps first in faculty quality among oceanography
programs nationwide. The scientific scope of the institution has grown
since its founding in 1903 to include biological, physical, chemical,
geological, geophysical, and atmospheric studies of the earth as a system.
More than 300 research programs are under way today in a wide range of
scientific areas. The institution has a staff of about 1,300, and annual
expenditures of approximately $100 million, from federal, state, and
private sources. Scripps operates the largest U.S. academic fleet with
four oceanographic research ships and one research platform for worldwide
exploration.