16 June 2008
DNA Precursors In Meteorite Confirmed As Extraterrestrial
by Kate Melville
Panspermia, the theory that life on Earth may have evolved from simple bacteria that arrived via meteorite is still a hotly debated topic amongst astrobiologists, but an important new discovery indicates that the basic building blocks of life - known as nucleobases - may be a far more likely extraterrestrial contender for kick-starting life on Earth.
The scientists involved, from the UK and the USA, say that the nucleobases in question, uracil and xanthine, were found in fragments of the Murchison meteorite which crashed in Australia in 1969. Most importantly, these nucleobases are almost certainly extraterrestrial in origin.
Reporting their findings in the journal Earth and Planetary Science Letters, the scientists explain how they tested the meteorite fragments to determine whether the molecules came from the solar system or were a result of contamination when the meteorite landed on Earth. Their analysis showed that the nucleobases contain a tell-tale heavy form of carbon which could only have been formed in space, as the same materials formed on Earth consist of a lighter variety of carbon.
Lead author, Imperial College's Dr Zita Martins, contends that 4 billion years ago large numbers of rocks similar to the Murchison meteorite rained down on Earth at the time when primitive life was forming. "We believe early life may have adopted nucleobases from meteoritic fragments for use in genetic coding which enabled them to pass on their successful features to subsequent generations," she suggests.
Imperial co-author, Professor Mark Sephton, believes the research is an important step in understanding how early life might have evolved. "Because meteorites represent left over materials from the formation of the solar system, the key components for life - including nucleobases - could be widespread in the cosmos. As more and more of life's raw materials are discovered in objects from space, the possibility of life springing forth wherever the right chemistry is present becomes more likely," he posited.
Source: Imperial College London