The Origin of Life on Earth

People have sought to explain the origin of organisms since at least the beginning of historical times. At the time of the Renaissance most Europeans believed that living organisms devel- 

Scientists do not believe that life is arising from non-life on Earth today, but, if life originated on Earth, as it apparently did, it must have developed from non-living materials. Current scientific views of when and how life might have originated and evolved are based upon imaginative chemical experiments in the laboratory, combined with studies of the fossil record and ways of dating events in the remote past. 

Early students of the origin of life were misled because they believed that Earth was very young, in part because no methods were available for dating ancient events. Today, suitable methods exist for determining the age of materials that are billions of years old, and the fossil record of ancient organisms has vastly improved. The evolution of living organisms 

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The deciding impulse which introduced biogenesis into scientific discussion came from Russia. After the upheavals of the civil war, that country was the subject of worried observation by the rest of the world. It was assumed that no great scientific achievements would be possible there. Then, in 1924, a book on the material basis of the origin of life on Earth appeared in Red Russia . Its author was Alexandr Ivanovich Oparin (1894-1980) from the Bakh Institute of Biochemistry in Moscow (Oparin, 1924). Basically, the Oparin hypothesis makes the following assumptions ... 

The question of the origin of life on Earth leads directly to the question of the formation of our planet, of the solar system and of the universe. The ancient philosophers, as we have seen, attempted to answer such questions, but the models which we discuss and argue about today were proposed by scientists only in the last century. 

While accepting the high quality of these results, Everett L. Shock from the Department of Earth and Planetary Research of Washington University, St. Louis, poses the critical question as to whether the many simulation experiments really help us in answering the question of the origin of life on Earth (Shock, 2002). 

Our mission is to explore the molecular universe with an understanding of all of the local molecular environments and constrain possible chemical reactions using the concepts of physical chemistry. With such a wide brief we need a focus and I have chosen the origins of life on Earth and on all planets - astrobiology. 

There is no one correct theory for the origin of life on Earth or any habitable planet, although many have been presented. The current set of ideas is summarised in Figure 1.5. Aside from the theory of creation, which seems particularly hard to test, the testable theories of the origins of life divide into two extraterrestrial or panspermia, the theory that life was seeded everywhere somewhat randomly and terrestrial, that life originated de novo on Earth or other habitable planets around other stars. The theories of terrestrial origin are more favoured but the recent discovery of habitable planets and life within any solar system suddenly makes panspermia more likely. 

Much of the electromagnetic spectrum has been used to investigate the structure of matter in the laboratory but the atmospheric windows restrict astronomical observations from Earth. Irritating as this is for astronomers on the ground, the chemical structure of the atmosphere and the radiation that it traps is important to the origins of life on Earth. The light that does get through the atmosphere, however, when analysed with all of the tools of spectroscopy, tells the molecular story of chemistry in distant places around the Universe. 

In the study of the origin of life on earth, the element carbon is essential. Carbon is a required component of the fundamental molecules of life amino acids, bases, and sugars. In addition, a large variety of carbon compounds is necessary in the complex biochemical cycles of living organisms. The physical and chemical nature and geometry of the carbon atom make it well suited to form the vast array of molecules involved in the chemistry of life. 

The first concerns the origin of life on earth as we know it, of our biological world. The second considers the possibility of extraterrestrial life, within or beyond the solar system. The third question wonders why life has taken the form we know, and it has as corollary the question whether other forms of life can (and do) exist is there artificial life It also implies that one might try to set the stage and implement the steps that would allow, in a distant future, the creation of artificial forms of life. 

The origin of life on Earth has challenged scientists and philosophers for many years. Experimental efforts to reconstruct the early events on Earth that may have led to life have been underway for more than 50 years and much of interest has been learned. Some have suggested that life on Earth arrived from some extraterrestrial source. Wherever it originated, it did so once. We are a long way from understanding the sequence of events, and there must have been a very large number of them, which eventually created life. Life is, after all, the result of an experiment of nature that we have not been able to replicate. 

Clearly, these ideas apply with equal force to RNA molecules. The only basic difference is that the RNA library has one letter different from that of DNA U replaces T. The retroviruses employ RNA as basic genetic material. Among scientists involved in efforts to understand the origins of life on Earth, RNA is widely... 

Conceptual framework of research on the origin of life on Earth... 

The main assumption held by most scientists about the origin of life on Earth is that life originated from inanimate matter through a spontaneous and gradual increase of molecular complexity. 

According to this view, life is made equivalent to a single molecular species, once it is capable of self-replication. It should be noted that this does not correspond to any form of life presently known on Earth and as such should rather be considered as a form of artificial life. The implication in the above definition is, however, that this form of life was the most likely initial source for the origin of life on Earth. Clearly, this operational deflnition emphasizes evolution as the main aspect of life. 

Commeyras, A., Boiteau, L., Vandenabeele-Trambouze, O., and Selsis, F. (2005). From prebiotic chemistry to the origins of life on Earth. In Lectures in Astrobiology, eds. M. Gargaud, B. Barbier, H. Martin and J. Reisse. Springer-Verlag, vol. I, part n, pp. 35-55. 

Q957). The Origin of Life on Earth, 3rd edn. Academic Press. 

Oparin, A.I. (1957). The origin of life on earth, 3rd ed. Oliver Boyd, Edinburgh London. 

Cohen, J. (1995) Getting all turned around over the origins of life on Earth. Science, 267, 1265. 

Berg RL. Some conditions for the appearance of life on earth. In Clarke F, Synge RLM, eds. Proc I Internat Symp The Origin of Life on Earth. New York Pergamon Press, 1959 169. 

By the way, born of water is also the name we might all bear as the origin of life on Earth took place in the oceans... 

More than 30 years of experimentation on the origin of life in the fields of chemical and molecular evolution have led to a better perception of the immensity of the problem of the origin of life on Earth rather than to its solution. At present all discussions on principal theories and experiments in the field either end in stalemate or in a confession of ignorance.2... 

A. N. Belozersky (1959b). Contribution to the discussion at the Symposium The Origin of Life on Earth (in Russian), Izdatelstvo Akademii Nauk SSSR, Moscow, p. 370. 

Somewhere around 9 or 10 million species of animals inhabit the Earth. The exact number will probably never be known. And, since the origin of life on Earth, uncounted millions of species have come and gone, only a small number of which left behind evidence of their passing. 

Photocatalysis is mostly thought of in terms of the photodegradation of molecules initiated either by oxidative or by reductive processes. However, photosynthesis may also result from a photocatalytic process, as observed for the reduction of C02 to formic acid by natural minerals. This reaction is the first step in an abiotic pathway for the synthesis of organic molecules and has been proposed to have played a role in the origin of life on earth [9]. 

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