The origin of life

Life is improbable, but under the favorable physicochemical conditions of the early Earth it did begin. These conditions included an appropriate surface temperature, the presence of liquid water, the availability of appropriate chemical ingredients, the presence of a magnetic field, and an environment in which there were redox contrasts, all set in the context of a dynamic planet experiencing periodic resurfacing. 

Life is also complex and the detailed chemistry of how the organic molecules which sustain and regulate life were formed is yet to be worked out. However, there was process in which simple molecules were synthesized to form complex polymers useful in the process of replication and the transmission of genetic information. Many believe that the nucleic add RNA was a precursor to the modem DNA and that life first developed in an RNA world. In addition the relevant energy sources were harnessed to facilitate life. Now these come mostly from sunlight, but in the early Earth they were probably chemical. 

Archaean, by 2.7 Ga microbial life was diverse and abundant. However, tradng the record further back in time brings greater uncertainties, but there is good evidence of sulfate reducing bacteria as far back as 3.5 Ga and some evidence for photosynthe-sising cyanobacteria as old as 3.8 Ga in the Isua sediments. 

A favored habitat for the emergence of life on Earth is in an oceanic hydrothermal system. This is consistent with the thermophilic character of the most ancient members of the tree of life. Such systems were abundant in the Archaean and would have provided the energy, nutrients and catalysts needed for complex organic synthesis, and hence for life. They may even have provided a mineralogical mechanism for the formation of the first living cells. 

Seeking to understand the origin of life is one of the greatest scientific questions we can ever pose, and for us as humans it is perhaps the most pertinent. For even a cursory examination of the complexities involved leads almost to incredulity. As Nisbet pointed out two decades ago in his book The Young Earth 

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After retirement he went to the Centre for Theoretical Studies at Coral Gables, Florida, where one of his main interests was the question of the origin of life. He died at Coral Gables on October 5, 1976. 

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... 

Chang, S., Desmarias, D., Mack, R., Miller, S. L., and Strathem, G. E. (1983). Prebiotic organic synthesis and the origin of life. In "Earth s Earliest Biosphere, Its Origin and Evolution" (J. W. Schopf, ed.), pp. 53-88. Princeton University Press, Princeton, New Jersey. 

This is a serious matter for further thinking and could have implications for pre-biotic chemistry and eventually, for the origin of life. 

In addition to the catalytic action served by the snRNAs in the formation of mRNA, several other enzymatic functions have been attributed to RNA. Ribozymes are RNA molecules with catalytic activity. These generally involve transesterification reactions, and most are concerned with RNA metabofism (spfic-ing and endoribonuclease). Recently, a ribosomal RNA component was noted to hydrolyze an aminoacyl ester and thus to play a central role in peptide bond function (peptidyl transferases see Chapter 38). These observations, made in organelles from plants, yeast, viruses, and higher eukaryotic cells, show that RNA can act as an enzyme. This has revolutionized thinking about enzyme action and the origin of life itself. 

Singer, T. P. In Biochemical Evolution and the Origin of Life, p. 203 edited by Schoffeniels, E. Amsterdam North Holland 1971. 

The ability of STM to image at the atomic scale is particularly exemplified by the two other chapters in the book. Thornton and Pang discuss the identification of point defects at Ti02 surfaces, a material that has played an important role in model catalyst studies to date. Point defects have been suggested to be responsible for much of the activity at oxide surfaces and the ability to identify these features and track their reactions with such species as oxygen and water represents a major advance in our ability to explore surface reactions. Meanwhile, Baddeley and Richardson concentrate on the effects of chirality at surfaces, and on the important field of surface chirality and its effects on adsorption, in a chapter that touches on one of the fundamental questions in the whole of science - the origins of life itself ... 

In the earlier years, in the absence of exact knowledge of microorganisms or chemistry, there had arisen much skepticism and bitter feeling over the question of the origin of life. One scientist who still held to the ancient ideas says of the views of another who doubted,... 

For a fuller discussion of this view of the origin of life, see Rose (1997)-... 

The learning process with respect to the problem of the origin of life took place in a manner similar to the three stages described by the French philosopher Auguste Comte (1798-1857) for the linear history of progress in human culture. These three stages are ... 

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 ... 

Various definitions have been proposed, and, depending on one s scientific standpoint, a suitable one may be available. Several of these definitions will be presented below. A completely satisfactory answer will, however, probably only be found when more detailed results on the origin of life become available. 

Haldane JBS (1928) The Origin of Life. Rationalist Annual 148 3. Reprinted in Science and Human Life, Harper Brothers, New York, 1933 Herrera AA (1942) Science 96 14... 

Oparin AI (1924) The Origin of Life, 1. Edition (Russian Proiskhozdenic Zhizni). Moskovskiy Rabochii, Moskau... 

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. 

Kasting JF, Eggler D (2002) 13th International Conference on the Origin of Life, Oaxaca, abstr p 45... 

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). 

The chondrules contained in the chondrites contain olivine, pyroxene, plagiok-lase, troilite and nickel-iron they can make up 40-90% of the chondrites. Chondrules are silicate spheroids, fused drops from the primeval solar nebula. Because of their differing constitution, chondrites are further subdivided one group in particular is important for the question of the origin of life, and has thus been intensively studied—that of the carbonaceous chondrites. 

These experiments provided the first proof that the question of the origin of life is a scientific problem which can be approached (and possibly solved) by using scientific methodology. 

However, there are also biogenesis models which do not require phosphate, such as the inorganic hypothesis of the origin of life proposed by Cairns-Smith (see Sect. 7.1), the thioester world proposed by de Duve (see Sect. 7.4) or the sulphur-iron world suggested by Wachtershauser (see Sect. 7.3). The RNA world (see Chap. 6), however, cannot exist without phosphate. 

In today s discussion of the origin of life, the RNA World (Chapter 6) is seen as much more important, and is much better publicized, than the protein world . However, nucleic acids and proteins are of equal importance for the vital metabolic functions in today s life forms. Peptides and proteins are constructed from the same building blocks (monomers), the aminocarboxylic acids (generally known simply as amino acids). The way in which the monomers are linked, the peptide bond, is the same in peptides and proteins. While peptides consist of only a few amino acids (or to be more exact, amino acid residues), proteins can contain many hundreds. The term protein (after the Greek proteuein, to be the first) was coined by Berzelius in 1838. 

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