We still don’t know just how the first life on Earth originated. One suggestion is that the building blocks arrived here from space; Now, a new study of several meteorites rich in carbon has added weight to this idea.
Using new and highly sensitive analysis techniques for these meteorites, a team led by scientists from Hokkaido University in Japan has discovered organic compounds that form the backbone of the DNA molecules common to all life as we know it — DNA and RNA.
Researchers analyzed three carbon-rich meteorites: the Murchison meteorite that landed in Australia in 1969, the Murray meteorite that landed in Kentucky in 1950, and the Tagish Lake meteorite that fell to Earth in 2000, and landed in British Columbia.
While meteorites have impacted our planet recently, they are really ancient space rocks, likely present in the early stages of the solar system or even earlier.
Carbon-rich meteorites are a treasure trove of organic compounds. When it comes to the appearance of DNA and RNA molecules on Earth, the compounds we’re particularly interested in are the nucleobases — the pieces that clump together, forming long chains of genetic information.
There are two main classes of nucleobases: pyrimidines and purines. Thanks to the astonishing sensitivity of their analysis techniques, the authors of the new study detected several pyrimidines in meteorite samples from which they previously escaped.
“We detected a variety of pyrimidine nucleobases and their structural isomers from Murchison extracts, most of which had not been previously detected in meteorites,” the team wrote in their paper.
The team wrote that experiments that simulated the contents of space materials suggested that many nuclear bases existed “outside,” “suggesting that these classes of organic compounds are ubiquitous in extraterrestrial environments both inside and outside the solar system.”
Why are these compounds so important? DNA and RNA strands possess a structural “backbone” consisting of the sugar phosphate chain. Nuclear bases stick to these sugars; In DNA, they pair up in specific ways, forming the “rungs” of the helical ladder.
The nuclear bases of purines and pyrimidines are always linked together within DNA because of their structure and the types of hydrogen bonds that can form. This means that the ratio of purine and pyrimidine nuclear bases is always constant within the DNA molecule.
These nuclear bases had emerged through photochemical reactions between different materials circulating in space, even before the formation of the solar system.
The authors suggest that during the Late Heavy Bombardment of the early Earth, roughly 4 to 3.8 billion years ago, a variety of these building blocks could have been delivered to our planet via meteorite collisions.
“Therefore, the influx of such organic matter played an important role in the chemical evolution of the primitive phase of the Earth,” they wrote.
We will gain more insight into this idea as sample missions to the asteroids Ryugu and Bennu provide us with more extraterrestrial material to study.
The uncontaminated samples will allow researchers to determine if these particles could have been brought here by meteorites. We can’t wait.
The search was published in Nature Communications.