BBC News
Thursday, 20 December, 2001, 00:00 GMT 

Life's sweet start
Did life's building blocks fall from the skies?
By BBC News Online science editor Dr David Whitehouse 

Life on Earth may have got off to a sweet start
nourished by sugar from space. 

The suggestion is based on the discovery of sugar in two
meteorites that are billions of years old. 

Researchers from the American space agency,
Nasa, say their study of the two space rocks has
revealed a range of organic substances called polyols -
the technical name for sugars. 

These sugar compounds were found in the Murchison
and Murray meteorites, which are believed to be
fragments broken off a much larger body. 

Backbone of life 

The Murchison meteorite was recovered in Australia in
1969; the Murray meteorite was picked up in Kentucky
in 1950. 

Both are examples of carbonaceous chondrite
meteorites and are believed to be fragments of much
older and larger bodies that once resided in the
asteroid belt between the orbits of Mars and Jupiter. 

It is known that meteorites contain many carbon-based
compounds - such as amino acids - that could
become the building blocks of primitive life. Analysis of
the Murchison meteorite found over 90 types of
amino acids. 

But to date, no conclusive evidence of sugars - also
crucial for life - have been found in meteorites. Claims
have been made, as far back as 1962, but there
was always the suspicion that terrestrial
contamination was the real source. 

However, the Nasa researchers, writing in the journal
Nature, say their detection method is "relatively
definitive". They add that as well as sugars common on
Earth, they have detected forms of sugar that are rare
on our planet. 

First steps 

According to Mark Sephton, of the UK's Open University:
"Sugars are important biologically because they provide
the carbon skeletons for many other molecules." 

Perhaps the most famous example here is DNA -
sugars provide part of the backbone for "molecule of
life". 

The presence of amino acids implies that life on Earth
might have been "seeded" by organic compounds
falling on to the planet. The discovery of sugar
molecules in the meteorites suggests that another
essential building block of life may have come from
space as well. 

The sugars may have been formed before the Solar
System itself was formed, by the action of starlight on
molecules resting on cold grains of dust drifting in
between the stars. 

When our Solar System was created, the sugar could
have become incorporated into small bodies, like
asteroids, that formed in the system's cold outer
reaches. 

When the asteroids broke up, fragments would have
fallen to Earth and delivered their life-forming
molecules. 

Mark Sephton says the findings suggest how "the first
chemical steps towards sweet life" were taken.

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