Simple, single-celled life is believed to have existed on Earth 3.9 billion years ago – almost immediately, when the Earth was cold enough for liquid water to surface. How could life arise so quickly? Researchers may have taken a big step forward in answering this question: a team from Japan and the USA discovered so-called nuclear bases in three meteorites – important building blocks for the DNA of genetic material. Scientists explain that these complex molecules may have formed in space before the formation of the solar system in the magazine Nature Communications.
“Our investigations show that there is a large variety of nuclear bases in meteorites,” according to the report of researchers led by Yasuhiro Oba of Hokkaido University in Japan. “These nuclear bases may have served as building blocks for the formation of DNA and RNA on early Earth.” For organisms to be able to reproduce and adapt to their environment through evolution, their blueprint must be storable and scrollable. The carrier of this plan is usually DNA, while RNA helps to copy this information. The actual information is stored in the sequence of nuclear bases.
Carbon is the central building block of all life on Earth: four more atoms can bond to a carbon atom and complex compounds, long molecular chains, and molecular rings can form. In chemistry, these carbon-based compounds are called “organic” because they form the basis of life. It has long been known that many organic substances can form in space. Even amino acids and sugar molecules have been detected in clouds of gas and meteorites that have fallen to Earth.
It can be said that the molecules are stable enough to survive the turbulent early stages of the planets
As a result, the hypothesis gained weight that the rapid emergence of life on Earth was driven by the influx of life’s building blocks from space. But how far has this cosmic support gone? Too far, as the study by Oba and colleagues now shows: With the help of new methods of analysis, researchers have been able to discover a large variety of nuclear bases in three intensively studied meteorites. These include adenine, thymine, guanine and cytosine – these four substances are the main information carriers in DNA.
The key to the Japanese team’s success has been the sensitivity of its measurement tools. “Our analysis method has been optimized to detect nucleobases at the lowest concentration down to one molecule in a trillion,” the scientists say. In fact, they find nuclear bases at concentrations as high as one in a billion. The detected abundance coincides with predictions from models of chemical evolution in the dense gaseous clouds that make up stars and planets.
Oba and colleagues conclude that the building blocks of DNA formed before the formation of the Sun and Earth. It appears to be stable enough to survive the turbulent formation of planets, accumulating in fragments of dust and rock, and then making its way to Earth through meteorites.
In turn, the formation of such molecules on young Earth is difficult. “Therefore, we suspect that the nuclear bases obtained from space contributed to the emergence of the genetic characteristics of the first life on Earth,” say the researchers.
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