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 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, Moffett Field, Calif. 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.
NASA's Exobiology Program provided funding for the research.