Extraterrestrial sugar found in meteorites suggests origins of life on Earth
An international team of scientists found sugars essential to life in two different meteorites. According to NASA, "the new discovery adds to the growing list of biologically important compounds that have been found in meteorites, supporting the hypothesis that chemical reactions in asteroids––the parent bodies of many meteorites––can make some of life’s ingredients. If correct, meteorite bombardment on ancient Earth may have assisted the origin of life with a supply of life’s building blocks."
The team discovered ribose and other bio-essential sugars––like arabinose and xylose––in two different meteorites. Ribose is a crucial component of RNA (ribonucleic acid) which acts as a messenger, copying and carrying instructions from DNA molecules for controlling the synthesis of proteins.
“Other important building blocks of life have been found in meteorites previously, including amino acids (components of proteins) and nucleobases (components of DNA and RNA), but sugars have been a missing piece among the major building blocks of life,” said Yoshihiro Furukawa of Tohoku University, Japan, lead author of the study published in the Proceedings of the National Academy of Sciences November 18.
Furukawa also stated that “the research provides the first direct evidence of ribose in space and the delivery of the sugar to Earth. The extraterrestrial sugar might have contributed to the formation of RNA on the prebiotic Earth which possibly led to the origin of life.”
The new research gives support to the possibility that RNA coordinated the structure of life before DNA. DNA carries the instructions for how to build and operate a living organism, however, RNA also carries information. Many researchers think RNA evolved first and was later replaced by DNA, given that RNA molecules have capabilities that DNA lacks. RNA can make copies by itself without "help" from other molecules, and it can also initiate or speed up chemical reactions as a catalyst.
The team plans to analyze more meteorites to have a better idea of the abundance of the extraterrestrial sugars, and see if the extraterrestrial sugar molecules have a left-handed or right-handed bias. As the NASA release explains, some molecules come in two varieties that are mirror images of each other, like your hands. Life on planet Earth uses left-handed amino acids and right-handed sugars. "Since it’s possible that the opposite would work fine––right-handed amino acids and left-handed sugars––scientists want to know where this preference came from. If some process in asteroids favors the production of one variety over the other, then maybe the supply from space via meteorite impacts made that variety more abundant on ancient Earth, which made it more likely that life would end up using it."