Chapter 6-3

The Chemicals of Life

In addition to searching for extraterrestrial life, we pursue the search for extraterrestrial life-related molecules in order to establish the universal nature of prebiotic chemical synthesis.

Recent discoveries show that comets, which seem to have remained unchanged since the formation of the solar system, may represent a unique storehouse of information about organic synthesis at the time of formation. We now have evidence that the organic molecules believed to be precursors of molecules essential for life are prevalent in comets. These discoveries have provided further support for the view that chemical evolution has occurred widely beyond the Earth. Comets may even have played a major role in the organic chemical evolution of the primitive Earth itself. Significant amounts of important precursor molecules could have been deposited on the primitive Earth by cometary impacts.

Meteorites, which provide us with solid samples of extraterrestrial material, represent another source of information about the occurrence of prebiotic chemistry beyond the Earth. In 1969, meteorite analyses provided the first convincing proof for the existence of extraterrestrial amino acids, a group of molecules necessary for life. Since then, a large body of information has accumulated to show that many more of the molecules necessary for life are also present in meteorites, and it now seems clear that the chemistry of life is not unique to the Earth. Future studies of meteorites should greatly contribute to the eventual understanding of the conditions and processes during the formation of the solar system and should provide clues to the relations between the origin of the solar system and the origin of life.

scale photo of the Murchison meteorite
Clue in a cosmic mystery.
A fragment of the Murchison meteorite, which fell on Australia in 1969. Organic matter of a type not produced biologically was found in the meteorite.

The atmospheres of the outer gas giant planets (Jupiter, Saturn, Uranus and Neptune) represent yet another extraterrestrial environment in which prebiotic chemistry can occur. In fact from our knowledge of the composition of Jupiter's atmosphere, many scientists consider it to be a good model for the primordial atmosphere of the Earth. Jupiter's atmosphere contains the same gases (hydrogen, methane, ammonia) that may have been present when the Earth's atmosphere formed, and violent lightning flashes were detected in Jupiter's clouds by the Voyager spacecraft.

With its abundant organic molecules and electrical energy, Jupiter may be the site of extensive prebiotic chemical reactions that reproduce what occurred on our own planet 4 to 4.5 billion years ago. We expect that further important information on this question will be provided by the Galileo spacecraft as it makes direct analyses of the turbulent atmosphere of this giant gaseous world.

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