- 04 May 2011 by Michael Marshall
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Kamis, 05 Mei 2011
Asteroids make life's raw materials
WERE asteroids the factories that created life's building blocks? For the first time, rocks from an asteroid have been shown to power the synthesis of life's essential chemicals.
The asteroid in question fell to Earth on 28 September 1969, landing on the outskirts of the village of Murchison in Victoria, Australia. Tests showed it was laced with amino acids and some of the chemicals found in our genetic material.
The discovery suggested that space was not the chemically sterile place it was once thought to be, and that organic chemistry was widespread. It hinted that the molecules life needed to get started could have been produced in space, before dropping to Earth.
But how did those molecules form? Raffaele Saladino of the University of Tuscia in Viterbo, Italy, and colleagues wondered if they could have been made deep inside the asteroids from which some meteorites break off. The team knew that a simple chemical present in space, called formamide, can be transformed into many biomolecules, so they used that as their starting point.
They obtained 1 gram of the Murchison meteorite, ground it to powder and removed all the organic molecules, leaving just the mineral. They mixed this with formamide and heated it to 140°C for 48 hours. The reaction produced nucleic acids - essential building blocks of DNA and RNA - as well as the amino acid glycine, carboxylic acids and a precursor to sugar (Origins of Life and Evolution of Biospheres, DOI: 10.1007/s11084-011-9239-0). This suggests the meteorite's parent asteroid was a chemical factory, Saladino says.
Crucially, the compounds produced are both metabolic and genetic, covering two key parts of primitive life, says Monica Grady of the Open University in Milton Keynes, UK, who was not involved in the study. "If you can catalyse both reactions in the same place, from the same starting material, that's obviously advantageous."
The ability to produce a range of essential molecules sets the meteorite mineral apart from Earth minerals, says Mark Sephton of Imperial College London. On Earth, the formation of each biomolecule tends to be catalysed by a different mineral, meaning they end up separated and less likely to form life.
Saladino's team also found that the meteorite mineral could stabilise RNA, thought by some to have been the first genetic material. RNA reacts with water and breaks down easily. Most minerals accelerate this process, but the team found that the Murchison mineral did not. "If RNA could be synthesised [inside the asteroid], this environment would stabilise it," Saladino says.