A MEETING WITH THE UNIVERSE

Appendix A-6



Exobiology

Amino acids have been synthesized non-biologically under conditions that simulate those postulated for the primitive Earth, followed by the synthesis of most of the biologically im portant molecules.

A laboratory model was developed for the evolution of cell structure from nonbiological precursors.

Ammonia and water molecules were detected in interstellar space with radio telescopes, followed by the discovery of many more important organic molecules and precursors.

Amino acids and other biologically significant organic substances have been found to occur indigenously in meteorites and to be of nonbiogenic origin.

Analysis of rock and soil samples returned from the Moon provided no evidence for past or present life and only traces of the precursors of amino acids.

Simulations of the atmospheric chem istry of the outer planets showed that these atmospheres may be sites where extensive abiotic synthesis of organic molecules is presently occurring.

Spectroscopic observation of comets has revealed the presence of biolog ically important ions, molecules, and fragments.

Viking lander experiments found no existing life or organic chemicals in the soil at two locations on Mars.

The Martian soil was found to possess intriguing chemical properties that mimic, in some respects, certain reactions of biological systems.

A third kingdom of microorganisms, the Archaebacteria, was shown to be distinct from the prokaryotes and eukaryotes, thus altering concepts of the earliest lines of descent of species on the Earth.

Clay minerals were found to markedly influence the rate and direction of chemical evolution processes.

Algae, bacteria, and fungi were discovered living inside rocks from the coldest and driest deserts of the Antarctic, which represent the closest terrestrial analog to the environment of Mars.

Microfossils were discovered in rocks 3.5 billion years old, a finding that pushed back the estimate of the time when life originated on the Earth to within the first billion years after the Earth was formed.

Nucleic acid polymers in the biologica size range were synthesized in a non-random manner, under geologically plausible conditions.



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