THE building blocks of DNA could have formed in space before Earth was born,
providing a starter kit of genetic material for life to evolve rapidly on Earth,
claim astrochemists in India. Their computer models of chemicals evolving in
space may explain why life emerged only 600 million years after the Earth formed
4.5 billion years ago.
The model also suggests that comets are packed with the building blocks of
life. If true, it backs up the idea that comets seed evolution when they smash
into planets.
Sandip Chakrabarti and his wife Sonali at the S. N. Bose National Centre for
Basic Sciences in Calcutta modelled how chemicals would evolve in an
interstellar cloud collapsing under gravity. The model began with a typical
cloud 7 light years across, containing a dozen elements including hydrogen,
carbon, oxygen and nitrogen.
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The model mimicked the cloud collapsing to 10 million kilometres across, over
a million or so years. The computer worked out the variations in temperature and
density of the cloud as this happened, and calculated the rates at which
different chemicals in the cloud would react.
The Chakrabartis focused on a series of four reactions for making the DNA
base adenine from hydrogen cyanide, a compound abundant in interstellar clouds.
And at the end of the simulation, the cloud was littered with adenine. In fact,
the Earth would have been showered with millions of tonnes of the DNA base if it
had formed in a chemical environment like this.
鈥淒NA bases produced in the collapsing cloud could have contaminated the
Earth,鈥� the Chakrabartis will report in the journal Astronomy and
Astrophysics. 鈥淭here should be many such planets in each galaxy where
DNA-based life should flourish.鈥�
But the idea remains controversial. Tom Millar of the University of
Manchester Institute of Science and Technology, whose database of chemical
reactions formed the basis of the new work, questions whether there would be
enough energy to drive the adenine reactions in the chilly depths of space at
just 10 degrees above absolute zero. Even if adenine did form, it might break
down again in some other process.
But Millar adds that the new results will prompt chemists to try their hand
at recreating the adenine-producing reactions in the lab. Sandip Chakrabarti
agrees that this is the way forward. 鈥淓verything hinges on the reaction rates,鈥�
he told 快猫短视频.
British researchers who suggested in 1977 that the ingredients of life
originated in space and were dispersed by comets are delighted by the Indian
findings. 鈥淚t鈥檚 yet another indication that the chemical feedstock of life could
be produced throughout the Universe, and nothing on Earth would reproduce that
grandeur of scale,鈥� says Chandra Wickramasinghe of the University of Wales at
Cardiff, who suggested the idea along with his colleague Fred Hoyle.
Max Bernstein, an astrochemist at NASA鈥檚 Ames Research Center in California,
agrees. 鈥淚t is reasonable to suggest that this molecule could have made the trip
by having been preserved in a comet,鈥� he says. He thinks the Indian study should
give further impetus for lab experiments to study the reactions, as well as
searches for signs of adenine in space.
