Organic and Pre-Biotic Chemistry of Meteorites and Comets: 1834-1996 by Norman Redington and Karen Ræ Keck
The recent discovery of possible microfossils in ALH84001 has generated another round in the debate about life in meteorites and/or comets. The claims that meteorites contain organic structures is as old as the study of meteorites and has led to at least three possible interpretations of the data: 1) organic compounds are of abiotic origin, but could give insight into the origins of life on earth; 2) they are ``fossils'' of life on the meteorite or on its parent body; and 3) meteorites or comets contain living materials. The last is connected to the idea of panspermia, the dispersion of life through the universe, which finds its contemporary expression in the work of Hoyle and Wickramasinghe. The debate, especially furious in the 1960's, has often centered on carbonaceous chondrites, which may contain the materials of the early solar system and/or prebiologic compounds formed in the solar nebula, in interstellar clouds, or on the chondrite's parent body. Scientists have also reported finding organic structures in other types of meteorites, even in iron meteorites. The length of the cycle of debate about organic materials in meteorites or comets appears in the XX Century to be 25-30 years.