Sweet Meteorites Scientists have discovered sugars in a meteorite,
adding to the list of complex organic molecules that have been
found inside space rocks.
December 20, 2001: Â A NASA scientist has discovered sugar and several related organic compounds in two meteorites -- providing the first evidence that another fundamental building block of life on Earth might have come from outer space.
Dr. George Cooper and co-workers from the NASA Ames Research Center found the sugary compounds in two carbon-rich (or "carbonaceous") meteorites. Previously, researchers had found inside meteorites other organic, carbon-based compounds that play major roles in life on Earth, such as amino acids and carboxylic acids, but no sugars.
Above: Pass the sugar? The carbonaceous Murchison meteorite,
pictured here, harbors sugar-related organic compounds. Image
copyright 2001 by New
England Meteoritical Services.
"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.
Above: Did comets and asteroids deliver the building blocks of life to Earth billions of years ago? New research lends credence to the idea. [more information]
"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 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.
Right : Â Sugars have also been found
in interstellar molecular clouds. Pictured is Jan M. Hollis of
the NASA Goddard Space Flight Center in Greenbelt, MD. Credit:
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.
These discoveries add an important new piece to the puzzle of the origins of life on Earth, and supports the notion that seeds of life might be spread far and wide around the cosmos.
Was Johnny Appleseed a Comet? --(Science@NASA) A new experiment suggests that comet impacts could have sowed the seeds of life on Earth billions of years ago.
Sugar in Space -- (Science@NASA) Scientists have discovered glycolaldehyde, a molecular cousin to table sugar, in an interstellar molecular cloud.
Right: The chemical structure of glucose and other naturally occurring sugars. Glucose is the primary "fuel" molecule used for generating energy in cellular respiration. Sugars like these are larger than the ones Cooper et al found in the Murchison and Murray meteorites. There is, however, preliminary evidence that these larger sugars might be present as well.
Scientists Discover Sugar in Space -- a National Radio Astronomy Observatory press release
Meteorites: One Lump or Two? -- The research paper, "Carbonaceous Meteorites as a Source of Sugar-related Organic Compounds for the Early Earth," appears in the Dec. 20th issue of Nature.
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