The Pop Sci Unscrambler: Making Hard Science a Little Less Hard
The Paper: Carbonaceous meteorites as a source of sugar-related organic compounds for the early Earth. Published in Nature, December 20, 2001.
The Author: George Cooper, et al.
The Gist: It is possible that if it weren't for sugar-bearing meteorites, you wouldn't be here.
When life was first cooked up on Earth billions of years ago, some of the ingredients may have been flown in by extraterrestrial visitors. Not by starship-piloting aliens, but by bits of asteroids and comets that fell from the sky when the planet was still a lifeless ball of rock. Scientists have long known that some meteorites contain basic chemicals needed for life, such as amino acids. Now a study of two 4.5-billion-year-old meteorites has found another ingredient in the primordial soup: sugar.
NASA Ames Research Center chemist George Cooper and colleagues examined bits of carbon-rich asteroid chunks known as Murray and Murchison, meteorites that streaked to Earth in 1950 and 1969, respectively. The scientists found one sugar and a range of sugar-related compounds, all members of the larger class of chemicals called polyols. These sugar molecules are not the same kind you taste when you bite into a doughnut, but they are essential parts of cell membranes, DNA, RNA, and cellular energy sources. Scientists first found polyols in meteorites back in the early 1960s but couldn't be certain the sugars weren't traces of earthly microbes. This time, we know for sure that the polyols came from space.
Cooper's group was able to prove it by isolating the polyols using a technique called gas chromatography/ mass spectrometry. In gas chromatography, a vaporized sample is injected into a pressurized stream of an inert gas, such as helium. The gas is then pushed through a coiled, narrow tube coated with a solvent. The solvent interacts differently with the sample's various components, causing each vaporized chemical to leave the end of the tube at a different time. Each chemical is then identified by a mass spectrometer.
After six years of chemical sorting, Cooper and colleagues identified a profusion of polyols and their isomers, or molecular variants. It's the wide range of isomers that shows these organic chemicals formed not on Earth, but when the meteorites' parent asteroids congealed out of the dust and gases of the early solar system. Life on Earth uses and produces only certain isomers, so those isomers are common while others are rare. But for the polyols found in the meteorites, every isomer is present. Further, the polyols are heavy, with much higher proportions of the isotopes carbon-13 and deuterium than in polyols found on Earth.
Of course, the same processes that created space sugars could have taken place here. We may never know if earthly life started on its own or rode in on a meteorite. But one thing's certain: If meteorites can sugar the Earth, they could do the same on some other planet too.
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