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MOLECULAR PALEONTOLOGY MELVlN CALVIN* The term "molecular paleontology" was invented to describe a rather special kind ofinterest and activity which has been going on for the last decade or so, and I do not think it has been used explicitly before in the sense in which we are using it today. I think it is worthwhile to say a few words to place this general subject in context. First of all, we are concerned , as is almost all science, with the nature oflife on the earth. One approach to the understanding ofthat nature is to ask the question: How did life appear on the earth? Classical paleontology, dealing as it does (or did) with theformed elements thatare visible in the rock, has mostly concerned itselfwith the ways in which various living things have changed during the course of geological time. But an extrapolation of the basic notion of change in evolution—as expressed by Darwin and, of course, others—backward in time must lead to a point at which the living organism (s) consisted simply of one variety of a multitude of varieties of molecular aggregates. It is surely not likely that the shape ofthe molecular aggregates which we now recognize as the foundation ofthe morphology ofthe organism is likely to have left its impression in the rocks, and we must ultimately, ofcourse, look for the shape ofthe molecule itself, rather than ofthe aggregates.This iswhatImeanbymolecularpaleontology—the search for the shapes and detailed intimate architecture of the molecules thatmay beleftin therocks, and to determinefrom that, ifpossible, something about the time and nature ofthe interface in the course ofmolecular evolutionbetween thechemicalpart ofevolutionaryhistory, during which one could not speak ofa "living" organism, and biological evolution [i].»Laboratory ofChemical Biodynamics, University of California, Berkeley, California 94720. The Alumni Fund Lecture, Northwestern University, Evanston, Illinois, November 6, 1968. The work described in this paper was sponsored, in part, by the U.S. Atomic Energy Commission and, in part, by the National Aeronautics and Space Administration. 45 There surely is some kind ofinterface, and evidence ofthat interface is not likely to be found in the form ofmorphological remains but rather in the form of the molecular architecture and architectural changes which occurred during that changeover from prebiological to biological evolution. What we would like to find are criteria, self-contained within the molecular aggregates, or molecular architecture itself, which will distinguish for us the origin, or give us some clue as to the origin, ofthe individual molecules or aggregates. What is the time scale we have to deal with? Figure ? shows a diagram of the geologic periods. The field ofclassical paleontology is concerned with the relatively short time ofthe 600-700 million years in which macroscopic morphological remains have been found in the rocks. (The list in the center offig. 1 gives the names ofthe Precambrian rocks ofwhich I will speak as we go along.) On the right-hand side offigure 1 are some of the bench marks ofevolutionary events. I think it is clear that we will be dealing only with the period before the Cambrian interface, and we will try to extend our molecular search back in time as far as we can go. The more interesting rocks for our purpose would, ofcourse, be Precambrian rocks, and figure 2 gives some idea ofthe distribution ofthe Precambrian outcrops throughout the world. An additional location is the southwest coast ofGreenland, where the formation is called the Ketilidian formation and is dated at about2,000 millionyears. The others ofwhich we are going to speak are scattered in North America (Nonesuch, Gunflint, Soudan, GreenRiver, Antrim, Mud Lake), Australia (Ediocara and Bitter Springs), Britain (Charnwood), and South Africa (Fig Tree—Swaziland and Onverwacht ). The North American rocks include some very young ones such as the Mud Lake in Florida (6,000 years old), the Green River Shale underlying Colorado and Wyoming (60 million years old), the Antrim Shale underlying Michigan (300 million years old), the Nonesuch Shale (1,000 million years old), the Gunflint (2,000 million years old), and the Soudan (2,500 million years old). The Australian rocks (Ediocara and Bitter Springs) are muchyoungerand are only barely Precambrian, being 650 and 800 million years old. The...


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