Washington (dpa) - Biologically significant sugar molecules could have rained with meteorites to Earth. Researchers conclude this from analyzes of very primitive sky stones.
The team led by Yoshihiro Furukawa from Tohoku University in Sendai (Japan) discovered, among other things, the sugar ribose, the central building block of the genome molecule RNA (ribonucleic acid). The ratio of the various carbon variants (isotopes) in the sugar clearly show an extraterrestrial origin, the team reported in the "Proceedings" of the US Academy of Sciences ("PNAS").
Sugars are central to all life forms we know and are involved in many biological processes. Last but not least, they set the framework of the hereditary molecules RNA and DNA. For a long time scientists have been studying the possibility that biologically important sugars from space have come to the young earth.
Already in the 1960s, researchers had found biological sugars such as glucose and arabinose in so-called carbonaceous chondrites, a group of carbonaceous, prehistoric meteorites. However, an extraterrestrial origin could not be proven at that time. In the early 2000s, scientists detected extraterrestrial sugar acids and sugar alcohols on the Murchison meteorite, a carbonaceous chondrite that hit Australia in 1969. However, the proven compounds have no particularly great biological importance, the researchers write Furukawa.
The team again examined the Murchison meteorite and two other carbonaceous chondrites. The researchers were able to detect all four types of so-called aldopentoses. These are certain sugars whose backbone contains five carbon atoms each: ribose, arabinose, xylose and lyxose. In each case, the scientists found a noticeable excess of the isotope carbon-13 in comparison to the earthly distribution, which proves an extraterrestrial origin. By contrast, sugars from soil samples around the impact point of the Murchison meteorite even show a markedly low proportion of carbon-13, which also speaks against contamination of the meteorite on Earth.
The researchers conclude from their analyzes that these biologically essential sugar molecules can arise under non-biological conditions in space. They identified in the laboratory for a process similar to the so-called formose, which produces sugar from aldehydes (dehydrated alcohols). Central sugars such as ribose may have rained from space to Earth, Mars and other young planets, contributing to the formation of biomolecules such as RNA, the researchers said.