Page:Concepts for detection of extraterrestrial life.djvu/7

 Preface

The principal objective of the search for life on another celestial body is to determine the state of chemical evolution if life has not yet arisen, or the state of biological evolution if life is present. A study of such life might contribute to a universal concept of the origin and nature of living systems. In addition, chemical and microscopic examination of any fossils from a pre-existing biota could provide equally valuable information.

This subject has provoked excessive speculation by some scientists, while others seem unaware of the implications of seriously confronting it. The quest for life in space rests on a reasonable degree of geological plausibility. A widely accepted theory argues that the known planets condensed under conditions compatible with the retention of water, ammonia and methane as gases in the primitive atmospheres. Laboratory experiments have demonstrated that primeval energy sources would have synthesized numerous biologically-significant molecules from these gases. Life developed on Earth when these gases and energies were also available to the other planets. Furthermore, it is both factual and perplexing that (except for helium) there is a closer resemblance between the elemental composition of living systems and the universe than there is between that of living systems and the rocky material in the terrestrial crust on and in which such systems are in intimate residence. Indeed, living matter on Earth displays a “unity of biochemistry” which may well be a principle with cosmic as well as terrestrial validity.

These arguments do not prove the hypothesis, but suggest that we cannot avoid the experiment. It is the purpose of this publication to describe briefly this experiment for the academic community and the public. Some of the methods which have been considered thus far for the detection of extraterrestrial life and life-related substances in the near reaches of space are presented.

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