UTS Voice
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Meteorites have provided crucial information about prebiotic chemistry.
The carbonaceous meteorite which fell at Murchison, Australian 1969 has provided valuable
clues abiotic synthesis. This meteorite formed very early, at the beginning of the formation
of the solar system and contains besides carbon and hydrated minerals several amino acids.
Many of these occurs in racemic proportion and the nitrogen isotopic ratios provide definite
evidence that they are not terrestrial contaminants acquired after the fall of meteorite.
Urey-Miller synthesis of formation of complex organic molecules in reducing environment
containing CO2, CH4, H2O, etc. have shown that it is easy to form these building blocks of
life by abiotic processes. However, initiation of biotic processes, if at all it can occur
from abiotic processes, is expected to take a long time. We know that earth formed early,
within 50 or 60 million years of formation of the solar system by collisional accretion of planetismals.
Thus, there was hardly any time available for transition from abiotic processes which is supposed to take
a long time.
In this context the hypothesis of Panspermia advanced by Helmholtz, Arrhenius and recently
favored by Hoyle and Wickramsinghe is noteworthy. If life seeds are present everywhere
in the universe, then life must occur wherever the conditions are conducive, within our
planetary system and outside. If we survey various bodies of the solar system we find that
Moon, Mars, Europa, Ganymede, Titan and comets in Kuiper belt or Oort’s cloud have frozen water on
or below their surface.
Life possibly began in space as shown by recent probes inside comets, a new study by scientists from
Cardiff University has said. Professor Chandra Wick-ramasinghe and colleagues at the
University’s Centre for Astrobiology have long argued the case for panspermia-the theory that
life began inside comets and then spread to habitable planets across the galaxy Now the team has
claimed that findings from space probes sent to investigate passing comets have revealed how the
first organisms could have formed. They said ‘The 2005 Deep Impact’ mission to Comet Tempel
discovered a mixture of organic and clay particles inside the comet.
One theory for the origins of life proposes that clay particles acted as a catalyst,
converting simple organic molecules into more complex structures. Incidentally, the
2004 ‘Stardust Mission’ to Comet Wild 2 found a range of complex hydrocarbon molecules potential
building blocks for life.
Wickramasinghe said radioactive elements could keep water in liquid form in comet
interiors for millions of years making them potentially ideal incubators’ for early
life. He said billions of comets in our solar system and across the galaxy contain far
more clay than the early Earth did. As such, the odds of life starting on Earth rather
than inside a comet stood at one trillion trillion (10 to the power of 24) to against one, he said.
“The findings of the comet missions, which surprised many, strengthen the argument for
panspermia. We now have a mechanism for how it could have happened. All the necessary
elements like clay, organic molecules and water are there. The longer time scale and the
greater mass of comets make it overwhelmingly more likely that life began in space than on earth,”
said Wickramasinghe. Inspite of absence of any evidence so far for origin of life, the subject
remains extremely fascinating. It is hoped that with improved technology, the coming century may
provide an answer to the question.
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