A discovery by a NASA scientist of sugar and several related organic
compounds in two carbonaceous meteorites provides the first evidence
that another fundamental building block of life on Earth may have
come from outer space. A carbonaceous meteorite contains carbon as
one of its important constituents.
Previously, researchers had found in meteorites other organic,
carbon-based compounds that play major roles in life on Earth, such
as amino acids and carboxylic acids, but no sugars. The new research
is reported in a paper, "Carbonaceous Meteorites as a Source of
Sugar-related Organic Compounds for the Early Earth," by Dr. George
Cooper and co-workers at NASA's Ames Research Center, in California's
Silicon Valley. The work is published in the Dec. 20 issue of Nature.
"Finding these compounds greatly adds to our understanding of what
organic materials could have been present on Earth before life
began," Cooper said. "Sugar chemistry appears to be involved in life
as far back as our records go." Recent research using ratios of
carbon isotopes have pushed the origin of life on Earth to as far
back as 3.8 billion years, he said. An isotope is one of two or more
atoms whose nuclei have the same number of protons but different
numbers of neutrons.
Scientists have long believed meteorites and comets played a role in
the origin of life. Raining down on Earth during the heavy
bombardment period some 3.8 billion to 4.5 billion years ago, they
brought with them the materials that may have been critical for life,
such as oxygen, sulfur, hydrogen and nitrogen. Sugars and the closely
related compounds discovered by Cooper, collectively called
"polyols," are critical to all known life forms. They act as
components of the nucleic acids RNA and DNA, constituents of cell
membranes and cellular energy sources.
"This discovery shows that it's highly likely organic synthesis
critical to life has gone on throughout the universe," said Kenneth
A. Souza, acting director of astrobiology and space research at Ames.
"Then, on Earth, since the other critical elements were in place,
life could blossom."
Cooper identified a small sugar called "dihydroxyacetone" and several
sugar-like substances, known as sugar acids and sugar alcohols, in
his study of the Murchison and Murray meteorites. All these are
important for life today. He also found one sugar alcohol, glycerol
(also known as glycerin), that is used by all contemporary cells to
build cell walls. In addition, Cooper discovered preliminary evidence
of other compounds that may contain larger sugars critical in
cellular metabolism, such as glucose.
There still are many unknowns though about the chemistry that existed
before the origin of life on Earth, according to Cooper. "What we
found could just be interesting space chemistry, and polyols could be
just relatives of the compounds that actually gave rise to early
life." More research on the meteorites is essential to determine the
significance of these findings, he concluded.
The Murchison meteorite, found in Australia in 1969, is a famous
example of a carbonaceous meteorite that contains numerous amino
acids and a variety of other organic compounds that are thought to
have played a role in the origin of life. The Murray meteorite, which
fell to Earth in 1950, is similar to Murchison in its organic content.
Related information about the Cooper paper in Nature can be found at:
http://www.nature.com
Further information about the Murchison meteorite is available at:
http://www.touchanotherworld.com/CurrentPhoto/CPcarbonaceous.htm
NASA's Exobiology Program provided funding for the research.
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