Carl Sagan once famously said that “We are made of star stuff.” The great astronomer was referring to the various elements formed long ago in the hearts of exploding stars, but scientists now think that his statement may prove to be just as true of life itself. Recent analysis of a large meteorite which burst into pieces over California in April last year has revealed the presence of potentially “prebiotic” organic molecules – the kind which may have provided the essential ingredients for life to evolve on Earth.
Could the building blocks for primordial life have come from outer space? Sandra Pizzarello, a biochemist at Arizona State University and lead author of a study on organic compounds found in the 2012 Sutter’s Mill meteorite, thinks it is a distinct possibility. Organic compounds, including some found among life on Earth, have been detected in many meteorites, and Pizzarello says that their composition indicates that “the precursors to the origins of life could have come from the extra-terrestrial material of meteorites.” Pizzarello told Space.com that "Since the origins of life are utterly unknown, the idea has its merits."
Initially, Pizzarello’s team found relatively few organic compounds when the Sutter’s Mill fragments were treated with solvents, but when the procedure was repeated under conditions mimicking an early Earth environment, the dissolved fragments released organic materials not seen before in meteorite studies. The find is significant because there now appears to be a far greater range of organic molecules which may have been delivered to our planet’s surface from outer space, and furthermore, those discovered in the latest tests are of a type which can bind together to form even more complex molecules.
Scientists generally believe that life would only have been possible if dissolved compounds were able to accumulate and cohere, and according to Pizzarello, the organic materials found in the Sutter’s Mill fragments “could be good for such a purpose, because they can form rudimentary enclosures to contain compounds useful to prebiotic evolution."
Extraterrestrial organic molecules were first detected in the Murchison meteorite which crash-landed in Australia in 1969, and ever since then, the idea that life’s building blocks originated in outer space has gathered momentum. Earlier this year, researchers announced that a computer model of the solar nebula – the cloud of dust and gas from which our Sun and Planets formed – revealed evidence that frozen water, ammonia, carbon dioxide and other molecules found in the cosmic cloud, may have combined to form organic materials when irradiated by the young Sun.
According to Fred Ciesla, a planetary scientist at the University of Chicago, and Scott Sanford, a NASA astrophysicist, the turbulent conditions of the solar nebula were ideal for breaking down and then recombining molecules to form complex compounds. The scientists say that over millions of years the process could have produced organic compounds such as amino acids and nucleobases – foundation materials for the production of proteins and DNA.
These materials would then have found their way into small rocky bodies which combined to form asteroids, comets and planets – including the Earth. Fred Ciesla suggests that our world may have always contained some of the critical molecules necessary for life, which were then topped up over millions of years by processes in the primordial soup and by visiting meteorites and comets.
Given that strikes by meteorites and the like were almost certainly more common hundreds of millions of years ago, might it not be possible that some of the building blocks of life were seeded from the stars? Studies such as that carried out on the Sutter's Mill meteorite fragments suggest that, at the very least, the suggestion is not to be easily dismissed. As Sandra Pizzarello says, "The analyses of meteorites never cease to surprise you ... and make you wonder."