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Meteorites could be life’s messengers
Posted: 10 August 2011

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Chemicals that existed in the early Solar System, which could have been an important source of the organic compounds that gave rise to life on Earth, have been found locked up within meteorites.

The new research strongly indicates that nucleobases, which are the building blocks of our genetic material, are capable of being transported to Earth within meteors that plunge through the atmosphere. Past research has revealed that amino acids, which join together to form proteins, exist in space riding on organic-rich meteorites called carbonaceous chondrites. It has, however, been difficult to prove that the nucleobases discovered on samples are not due to the contamination from sources on Earth.

Meteorites contain a large variety of nucleobases, an essential building block of DNA. Image: NASA’s Goddard Space Flight Center/Chris Smith.

The research team, which includes Jim Cleaves of Carnegie’s Geophysical Laboratory, were funded by the NASA Postdoctoral Program and used spectroscopy techniques to purify and analyse varies samples from 11 different carbonaceous chondrites and one ureilite, a rare type of meteorite with unusual chemical compositions that possibly come from colliding asteroids. It was discovered that two of the chondrites contained nucleobases and compounds that are structurally similar, serving as analogues of nucleobases, and at least three of these analogues are rare in terrestrial biology with very small concentrations in soil and ice samples in close proximity to where the meteorites were discovered.

“Finding nucleobase compounds not typically found in Earth’s biochemistry strongly supports an extraterrestrial origin,” says Cleaves, whose research is set to be published this week in the Proceedings of the National Academy of Sciences.

In order to test their conclusion the team devised an experiment to reproduce nucleobases and their analogues with the help of chemical reactions involving ammonia and cyanide; two ingredients that can be found in space. While the synthesised material was similar to the nucleobases found in carbonaceous chondrites, there was one main difference – the relative abundances varied and is believed to be due to the thermal and chemical processes that a nucleobase-ladened meteorite is subjected to on its journey through space.

With these results the scientists believe that the earliest forms of life here on our home planet may have arisen thanks to the materials that the meteorites delivered to our soil. “This shows us that meteorites may have been molecular tool kits which provided the essential building blocks for life on Earth,” says Cleaves.