Key Takeaways:
- Meteorites that have fallen to Earth contain all five of the bases that store genetic information in DNA and RNA.
- These nucleobases are adenine, guanine, cytosine, thymine, and uracil, which are essential for life on Earth.
- The presence of these bases in meteorites adds to the evidence that life’s building blocks may have originated in space.
- Researchers developed a sensitive technique to extract and analyze organic compounds in meteorite dust, allowing for the detection of these bases.
- While some compounds in meteorites may have originated from space, others could be due to Earthly contamination.
Meteorites that have impacted Earth within the past century have yielded a remarkable discovery: they contain all five of the bases responsible for storing genetic information in DNA and RNA. This groundbreaking finding, reported by scientists in Nature Communications on April 26, provides valuable insights into the origins of life on our planet.
The five nucleobases in question – adenine, guanine, cytosine, thymine, and uracil – are fundamental components of the genetic code found in all known life forms on Earth. The mystery of whether these essential building blocks of life originated in space or formed through the intricate chemistry of our planet has long intrigued scientists. While this discovery doesn’t definitively answer that question, it significantly strengthens the hypothesis that life’s precursors may have their roots beyond Earth.
Scientists have been detecting traces of adenine, guanine, and other organic compounds in meteorites since the 1960s. However, the presence of uracil, cytosine, and thymine had remained elusive until now. According to astrochemist Daniel Glavin from NASA’s Goddard Space Flight Center in Greenbelt, Maryland, “We’ve completed the set of all the bases found in DNA and RNA and life on Earth, and they’re present in meteorites.”
The breakthrough was made possible by a novel extraction technique developed by geochemist Yasuhiro Oba and colleagues at Hokkaido University in Sapporo, Japan. This method gently extracts and separates various chemical compounds from liquified meteorite dust, enabling precise analysis. Notably, this technique has significantly higher sensitivity than previous methods.
Previously, Oba’s team used this technique to discover ribose, a sugar essential for life, in three separate meteorites. In their latest study, they collaborated with NASA astrochemists to analyze four meteorite samples, including one of those previously found to contain ribose. Using their innovative extraction approach, they measured the abundances of nucleobases and other life-related compounds in meteorites that fell decades ago in Australia, Kentucky, and British Columbia.
The results were astonishing. In all four meteorite samples, the researchers detected and measured adenine, guanine, cytosine, uracil, thymine, as well as several compounds closely related to these bases and a handful of amino acids. The technique’s mild extraction process, using cold water rather than harsh acids, helped preserve these fragile nucleobases, making it more akin to a cold brew than a hot tea.
To further validate their findings, the researchers compared the chemical abundances in the meteorites with those in soil collected from the Australian impact site. While some compounds showed higher levels in the meteorites, indicating their possible extraterrestrial origin, others, such as cytosine and uracil, were up to 20 times more abundant in the soil. This discrepancy raises the possibility of terrestrial contamination, as noted by cosmochemist Michael Callahan of Boise State University.
Although not all experts are entirely convinced of the extraterrestrial origin of these compounds, Glavin and his team point to specific detected chemicals that support this hypothesis. They identified isomers of the nucleobases, which have the same chemical formulas but different molecular arrangements, in the meteorites but not in the soil. This absence in the soil suggests that tese isomers likely came from space, strengthening the argument for an interplanetary origin.
To gain further clarity on this matter, scientists are looking to pristine asteroids as potential sources of these meteorites. Yasuhiro Oba’s team is already using their extraction technique on samples from the surface of the asteroid Ryugu, brought to Earth by Japan’s Hayabusa2 mission.
“We’re really excited about what stories those materials have to tell,” Glavin says, emphasizing the potential for these celestial samples to provide crucial insights into the origins of life on Earth and the possibility of life beyond our planet.
