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We're all aliens... how humans began life in outer space

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The mystery of how the building blocks of biology came to be on Earth may finally have been solved

As scientific mysteries go, this is the big one. How did life on Earth begin? Not how did life evolve, but how did it start in the first place? What was the initial spark that lit the fire of evolution?

Charles Darwin solved the mystery of life's wondrous diversity with his theory of natural selection. But even he was flummoxed by the ultimate mystery of mysteries: what led to the origin of life itself?

In trying to answer the problem, scientists have turned to the stars, or at least the "builders' rubble" of meteorites and comets left over from the formation of our solar system some five billion years ago. These space rocks, they believe, could help to explain why life began here on Earth.

In fact, a growing body of evidence is now pointing to deep space as the possible source of the raw materials that formed the building blocks of life. The latest study, which focused on a class of meteorites that fell on to the Antarctic ice sheet, also suggests that life's origins may have been extraterrestrial.

An analysis of the meteorites has revealed that these rocks can be induced, under high pressures and temperatures, to emit nitrogen-containing ammonia, a vital ingredient for the first self-replicating molecules that eventually led to DNA, the molecule at the heart of all life.


Tests have also shown that the nitrogen in the ammonia released by the meteorite is composed of unusual isotopes, indicating an extraterrestrial origin rather than contamination from a terrestrial source.

Professor Pizzarello and her colleagues believe that similar meteorites falling to Earth about 4 billion years ago could have produced a constant and replenishable supply of ammonia, and hence nitrogen, which was so necessary for the formation of the first self-replicating molecules.

Previous studies of fossilized microbes in ancient rocks have shown that primitive life must have existed at least 3.5 billion years ago. Yet little is known of the time before that when life originated, except that it must have been very inhospitable.

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