How life arose on Earth in the first place is one of science’s deepest mysteries, according to New Atlas. Evidence is mounting that critical building blocks may have been transported to Earth from space. A new study makes this seem more likely,Because scientists have now found the last two DNA nucleobases in meteorites, two nucleobases that had not previously been found in extraterrestrial samples.
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DNA and RNA are made up of five organic molecules called nucleobases — adenine, cytosine, guanine, thymine and uracil. Adenine, guanine and uracil have all been found in meteorite fragments before, but researchers in the new study have now identified cytosine and thymine in meteorites for the first time.
The team said that the two nucleobases had not been discovered in the past, possibly because their structure is more fragile than other nucleobases. Typically, when scientists want to examine a meteorite sample for compounds, they put the meteorite particles in hot formic acid and then analyze the molecules in the resulting solution. But this process destroys some compounds.
So in the new study, the researchers tried cold water instead of hot “meteorite tea.” This gentler process, coupled with more sensitive analytical instruments that can detect smaller numbers of molecules, allowed the team to finally find the fragile cytosine and thymine.
Although all the ingredients to make DNA and RNA may have been present in ancient asteroids and comets, it is unlikely that they would have started forming these complex polymers in space. But it does support the idea that these ingredients originated in space before being deposited on Earth, where they could then be used by emerging life forms.
“We now have evidence that by the time life emerged, the full set of nucleobases used in life today may already have been on Earth,” said Danny Glavin, co-author of the study.
The full set of five nucleobases joins a growing list of life-critical compounds detected in meteorites and comets. This includes amino acids and their precursor molecules, sugars, organic compounds, molecules with life-specific structures, and even entirely new proteins.
The team also said that new colder, gentler extraction techniques could be used to make future analyses of extraterrestrial samples, including those returned by probes like Hayabusa-2 and OSIRIS-REx, more accurate.
The research was published in the journal Nature Communications.