HOW life on Earth began is a question that keeps people up nights. Without
the answer, we鈥檙e somehow doomed to stay rootless.
Not surprisingly, it鈥檚 inspired some astonishing experiments and theories.
Back in the 1950s, for example, at the University of Chicago, Stanley Miller had
a go at recreating the early Earth鈥檚 atmosphere in a jar. Not having any
lightning to hand, he passed a high voltage through the jar鈥攁nd produced
amino acids. Here was evidence of how biological molecules could have been
created on a barren Earth.
Unfortunately, getting from this clutch of amino acids to an organism capable
of self-replication and evolving into the complex cells we see today, replete
with DNA, RNA and proteins was鈥攁nd is鈥攓uite another matter.
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One of the most outlandish ideas emerged in 1977, when Fred Hoyle and Chandra
Wickramasinghe proposed that simple life forms were born in space and brought
here by comets. The idea was too much for many.
But then, in 1994, astronomers found the tell-tale spectral lines of the
amino acid glycine shining out from an interstellar cloud called Sagittarius B2.
Such clouds are where stars, planets and even comets form. For Hoyle and
Wickramasinghe, it was a first step towards vindication.
This week, Indian scientists have unveiled what looks to be a further boost
for the life-from-space theory
(see p 4). Using a computer model they found that
interstellar clouds can produce vast amounts of adenine, one of the four
chemical bases that make up DNA.
Unfortunately, finding spectral evidence of DNA bases floating in space is
likely to be difficult, because the energy that bathes these clouds is often too
low for substances such as adenine to generate a detectable signal. But there
may be another way to test the idea鈥攂y simulating nebular chemistry here
on Earth.
Early attempts to do this in the 1970s did produce adenine. Today,
researchers, such as Lou Allamandola and his colleagues at NASA Ames Research
Center in California, have perfected the art of recreating space in the lab.
They generate high vacuums and ultra-cold temperatures, add in the gases and
dust found in interstellar clouds, and bathe them in ultraviolet 鈥渟tarlight鈥�.
They have managed to produce not only common biochemicals, but also tiny
vesicles that resemble empty cells. Allamandola suggests that in the heart of
comets, essential biological molecules may be jiggled into these vesicles, so
when the comets hit Earth, they are ready to spring into life.
It will be intriguing to see if, with the same starting point as the Indian
theoreticians, Allamandola鈥檚 team, or one similar, can detect adenine. If they
can, it won鈥檛 prove Hoyle and Wickramasinghe right, but it will take us a step
closer in the quest for our first ancestor.
