We still do not know how the first life appeared on Earth. One suggestion is that the building blocks arrived here from space; now, a new study of several carbon-rich meteorites has added weight to that idea.
Using new analytical techniques that are extremely sensitive for these meteorites, a team led by scientists from Hokkaido University in Japan has detected organic compounds that form the backbone of nucleic acid molecules common to all life. as we know it – DNA and RNA.
The researchers analyzed three carbon-rich meteorites: the Murchison meteorite who landed in Australia in 1969, the Murray meteorite which landed in Kentucky in 1950, and the Tagish Lake meteorite which fell to Earth in 2000, landing in British Columbia.
While meteorites hit our planet fairly recently, they are genuine old space rocks, likely to have existed 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 emergence of DNA and RNA molecules on Earth, the compounds we are particularly interested in are nucleobases – the elements that stack together to form the long chains of genetic information.
There are two major classes of nucleobases: pyrimidines and purines. Using the incredible sensitivity of their analytical techniques, the authors of the new study detected several pyrimidines in their meteorite samples that had escaped detection.
“We detected a wide variety of pyrimidine nucleobases and their structural isomers from the two Murchison extracts, most of which had not been previously detected in meteorites,” the team writes in their article.
Experiments that had simulated the contents of space materials had suggested the presence of various nucleobases “out there”, “suggesting that these classes of organic compounds are ubiquitous in extraterrestrial environments inside and outside the solar system” , the team writes.
Why are these compounds so important? Both DNA and RNA strands have a structural “skeleton” consisting of a sugar-phosphate chain. Nucleobases bind to these sugars; in DNA they pair up in a specific way, forming the “rungs” of the helix-like ladder.
Purine and pyrimidine nucleobases always bond in DNA due to their structure and the types of hydrogen bonds they can form. This means that the ratio of purine and pyrimidine nucleobases is always constant in the DNA molecule.
These nucleobases would have emerged through photochemical reactions between the different materials wandering through space, even before the formation of the solar system.
The authors suggest that during the late period of heavy bombardment from early Earth, around 4 to 3.8 billion years ago, a diverse range of these building blocks could have been delivered to our planet via meteor impacts.
“Therefore, the influx of these organic materials is considered to have played an important role in the chemical evolution of Earth’s primordial stage,” they write.
We’ll have more information on this idea as sample missions to the Ryugu and Bennu asteroids provide us with more extraterrestrial material to study.
The uncontaminated samples will allow researchers to further establish whether these molecules could have been brought here by meteorites. We can’t wait.
The research has been published in Nature Communication.