The hypothesis that meteorite bombardment of prehistoric Earth might have kick-started the development of biological life on the planet is alive and well, and has been slowly gaining increasingly more support from the scientific community over the years.
Now, an international team of researchers has detected ribose and other bio-essential sugars, including arabinose and xylose, in two individual carbon-rich meteorites called NWA 801 (type CR2) and Murchison (type CM2).
While certain other components of life-as-we-know-it have already been found in meteorites in the past, sugars have remained elusive.
“The research provides the first direct evidence of ribose in space and the delivery of the sugar to Earth. The extra-terrestrial sugar might have contributed to the formation of RNA on the prebiotic Earth which possibly led to the origin of life,” said lead author Yoshihiro Furukawa of Tohoku University in Japan.
One of the leading hypotheses regarding the emergence of the first replicator from non-organic matter holds that DNA – the template for all life on Earth – was preceded by RNA due to its various exclusive features, such as the ability to make copies of itself without the involvement of any other molecules.
The new study provides some indirect support for the above hypothesis due to the absence of 2-deoxyribose (the sugar present in DNA) in the powdered samples of the aforesaid meteorites, suggesting a potential “delivery bias of extra-terrestrial ribose to the early Earth”.
One explanation for the findings would have causality reversed and maintain that meteorites were “seeded” via contact with Earth, rather than vice versa, yet the carbon isotope present in NWA 801 and Murchison (13C) would suggest otherwise, because almost 99% of the carbon found on Earth is of the lighter 12C variety.
As a next step, the team plans to analyse whether the extra-terrestrial sugar molecules have a “left-handed” or a “right-handed” bias, as that might provide some clues as to why our own planet uses “right-handed” sugars to the exclusion of their “left-handed” counterparts.
The paper was published in the Proceedings of the National Academy of Sciences of the United States of America (PNAS) on 18 November 2019.