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Life is Sweet: Sugar-Packing Asteroids May Have Seeded Life on Earth
By Robert Roy Britt
Senior Science Writer
posted: 02:00 pm ET
19 December 2001
Asteroids may have delivered the sugar on which life first licked its lips.
A new study has found sugar-like substances in meteorites that are chips off old asteroid that fell to Earth. The newly found chemicals are considered critical ingredients for all living things, and the discovery adds to a growing pile of evidence suggesting that life on Earth was seeded from space billions of years ago.
It also implies a greater chance that asteroids seeded life on other planets, including Mars.
Add water and sugar
Theory holds that Earth was harsh, dry and barren after its formation roughly 4.5 billion years ago. Comets may have brought water that filled the oceans. And in recent years, a growing number of scientists have warmed to an idea generated in the 1960s that comets and asteroids delivered other ingredients needed to jumpstart life. Catastrophic impacts could have supplied amino acids and other organic compounds used in biology.
Many of the necessary ingredients for life's recipe have been found to exist in comets and asteroids by studying them from afar. Harder evidence has come from space rocks that fell to Earth.
One class of ingredients had not been found, however.
Polyhydroxylated compounds, or polyols, include the sugar you buy in a store, sugar alcohols and sugar acids that are vital to all known life forms. The compounds act as energy sources for all organisms, they help build proteins and cell membranes, and they are components of RNA and DNA, the software of life.
| The new study found a variety of polyols in two meteorites, both thought to have originated in the main asteroid belt between Mars and Jupiter.
The study was led by George Cooper of NASA's Ames Research Center in California and will be presented in the Dec. 20 issue of the journal Nature.
"By discovering sugar compounds in meteorites, we now know that one more ingredient for the recipe of life was present in the early solar system," said Mark A. Sephton of the British Open University.
Murchison, which landed in Australia in 1969, has been the subject of much study and speculation.
A group of Russian researchers claims to have found signs of extraterrestrial organisms in the rock. But other scientists have dismissed the claims, saying the apparent fossilized life forms were likely due to terrestrial organisms taking up residence in the rock shortly after it hit the ground.
Murchison lives in the media shadow of another meteorite, called ALH84001, in which NASA researchers said in 1996 that they saw signs of ET, likely of Martian origin. Those claims, too, are disputed and no consensus has been reached.
The new study, however, appears not to be as controversial. And it clears up confusion generated by previous similar findings of sugar-like substances, which involved meteorites that had been on Earth for several decades before being found and studied. Scientists say those rocks may have been contaminated with sugars that originated on Earth. And studies of them did not yield a complex array of sugars and so remained inconclusive.
The new study found a variety of sugars with varying structures, some very rare on Earth, Sephton told SPACE.com. While some contamination cannot be ruled out, he said, some of the sugars very likely are of extraterrestrial origin.
Life on other planets
Further work is needed to determine the precise extent to which sugars exist in asteroids, he said. Meanwhile, the findings show that space rocks could be the cosmic storks that carry life's seeds elsewhere, too.
"As the delivery of meteorites is a process that is not exclusive to the Earth, similar materials will have arrived on other planets such as early Mars or as-yet undiscovered worlds in other solar systems," Sephton said. "The possibility of discovering life elsewhere in the solar system or universe is now greater."
Other studies have shown that meteorites travelling between planets could carry dormant life from one place to another. If life forms or fossils are ever found on Mars, scientists will be eager to learn whether they are related to life on Earth.
Origin of sugar
The new study leaves a nagging question: If there is sugar in space, how did it get there?
Cooper, the study leader, suggests along with his colleagues a root source for the sugars found in the meteorites. Precursors to the sugars may originally have formed in interstellar space, where dust, ice water, ammonia and carbon monoxide were stirred by starlight in a giant cloud that later formed our Sun and solar system.
These simpler sugar-like substances, if they survived the formation of the Sun, could then have gotten caught up in asteroid formation, Sephton said.
"What happened next is less clear," says Sephton. But there is ample evidence, he added, that "simple interstellar molecules were stewed in water and condensed to form more complex molecules, perhaps helped along by inorganic catalysts."
Astronomers have long said we are all stardust; all the elements and compounds known to exist were forged in stars. Increasingly, it appears we may also owe our existence to space rocks.
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