How did life first emerge on the once-barren rock we call Earth? It’s one of science’s most tantalising and enduring questions.
Over the past few decades, scientists have started to identify the organic molecules necessary for life on meteorites – chunks of rock from comets or asteroids that survive the perilous fall to Earth. Now, a new study from Hokkaido University, Japan, provides further evidence that life’s essential building blocks may have travelled here from space.
Nucleobases are necessary for building DNA, the strands of genetic material that carry the instructions to build a living creature, and RNA, a type of messenger molecule that, in most living things, carries these instructions from DNA to control the synthesis of proteins.
Nucleobases like guanine and adenine, core components of DNA, have been detected in meteorites in the past. But other nucleobases, known as pyrimidines, haven’t been detected in meteorite samples until now.
In this new study, published today in Nature Communications, the researchers used state-of-the-art analytical techniques to enable them to identify traces of nucleobases on a tiny scale. The researchers analysed three carbon-rich meteorites: the Murchison meteorite, which crash-landed at Murchison, Victoria, in 1969, the US-based Murray meteorite, which landed in Kentucky in 1950, and the Tagish Lake meteorite, which landed in Canada in January 2000. Alongside the nucleobases already detected in other meteorites, the researchers identified previously undetected pyrimidines, including cytosine and thymine, the other two bases found in the DNA molecule.
That amounts to, “the detection of all primary DNA/RNA nucleobases in the same meteorite,” says lead author Yasuhiro Oba, of Hokkaido University. It’s a remarkable find.
“This means such nucleobases would have been provided to Earth before the onset of life, and could have played a role in the emergence of genetic function in the environment.”
So how did these organic compounds, so crucial to the formation of life, emerge on floating rocks in the middle of space?
Oba believes these compounds may have been generated by photochemical reactions on rocks floating in interstellar space, before being incorporated into asteroids as the solar system formed. Their eventual delivery to Earth, hitch-hiking aboard the meteorites that commonly struck Earth during its early formation, may have been the spark that kicked off the evolution of early life.