Meteorites Deliver Nucleobases to Earth
New research, published the week of August 8-12 in the Proceedings of the National Academy of Sciences, indicates that certain nucleobases do reach the Earth from extraterrestrial sources, by way of certain meteorites, and in greater diversity and quantity than previously thought.
Extensive research has shown that amino acids, which string together to form proteins, exist in space and have arrived on our planet piggybacked on a type of organic-rich meteorite called carbonaceous chondrites. But it has been difficult to similarly prove that the nucleobases found on meteorite samples are not due to contamination from sources on Earth.
The research team, which included Jim Cleaves of Carnegie’s Geophysical Laboratory, used advanced spectroscopy techniques to purify and analyze samples from 11 different carbonaceous chondrites and one ureilite, a very rare type of meteorite with a different type of chemical composition. This was the first time all but two of these meteorites had been examined for nucleobases.
“Finding nucleobase compounds not typically found in Earth’s biochemistry strongly supports an extraterrestrial origin,” Cleaves said.
The team tested their conclusion with experiments to reproduce nucleobases and analogs using chemical reactions of ammonia and cyanide, which are common in space. Their lab-synthesized nucleobases were very similar to those found in the carbonaceous chondrites, although the relative abundances were different. This could be due to chemical and thermal processing that the meteorite-origin nucleobases underwent while traveling through space.
These results have far-reaching implications. The earliest forms of life on Earth may have been assembled from materials delivered to Earth by meteorites.
“This shows us that meteorites may have been molecular tool kits, which provided the essential building blocks for life on Earth,” Cleaves said.