DNA Space-Raced to Earth?

By William Scribe

Claims that life fell to Earth from outer space have received a boost this week. A new analysis of a meteorite has revealed that it contains chemical precursors of DNA and RNA which must have formed in space.

This is another piece in a fast-growing jigsaw which points to life being seeded on Earth from outer space soon after the planet formed 4.5 billion years ago.

In recent years astronomers have discovered organic chemicals hanging about in clouds of dust between stars as well as catching a lift on comets – astral bodies which could easily transport life across the vast tracts of space.

The chemicals discovered in the meteorite are uracil, a component of RNA, and xanthine which is often formed from guanine. Whilst xanthine is occasionally found in genetic material, guanine is one of the four major components of both RNA and DNA. The report appears in the journal Earth and Planetary Science Letters.

"The two [molecules] present in the meteorite are definitely extraterrestrial," says astrobiologist and lead author Zita Martins of Imperial College London.

She says it's unclear whether they were synthesised on the meteorite's parent asteroid or were formed in space and then stuck to the meteorite. "But we know that they may be formed in a variety of cosmic environments."

From there, the molecules "were delivered ready-made to the early Earth," says astrobiologist and co-author Mark Sephton, also of Imperial College London. "If the early solar system was a store cupboard, it would have many of the simplest ingredients for the recipe of life."

That life may have arrived on Earth from space is not a new idea. Millennia before Sir Fred Hoyle and Chandra Wickramasinghe popularised the idea in the late 1970s, the Ancient Greek philosopher Anaxagoras was wondering if life was seeded from the cosmos in 460 BC.

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