Is the Early Evolution of Life Related to the Development of the Earth's Core?

The Bakerian lecture, 1967 reversals of the Earth's magnetic field

This paper is an account of the Bakerian Lecture given to the Royal Society on 15 June 1967. Reversals of the Earth’s magnetic field can be studied in the magnetization of lavas and sediments on land, in the magnetization of deep sea cores and in the magnetic pattern on the ocean floor. The lavas give radiometric dates but not a continuous sequence; the cores give continuity, great detail and a resolution as fine as 1000 years; the magnetic pattern gives information all through the Tertiary and connects the spreading of the ocean floor with the radiometric time scale. The dynamo theory of the Earth’s magnetic field may be able to account for reversals as an instability in the dynamo, but only models with a finite number of degrees of freedom have been investigated. Spreading of the ocean floor is believed to be associated with convective motions in the upper mantle, although there are difficulties connected with the equality of the oceanic and continental heat flows. There is some evidence for the extinction of radiolaria at times of reversal of the magnetic field; it has been suggested that this is due to the effect of the field on cosmic rays but this appears impossible. If the extinctions are due to the reversals, the mechanism is unknown. Reversely magnetized rocks are more highly oxidized than normally magnetized ones. The cause of this is unknown and is one of the outstanding problems of Earth science.

Criteria for the emergence and evolution of life in the solar system

During the past years we have explored most of the bodies of the solar system by means of the Apollo, Venera, Viking, Voyager, and other space missions. We are now in a better position to be able to compare the conditions of other planets and satellites with those of the Earth in order to determine what is unique about our planet which permitted the emergence and evolution of life on it. On the basis of this and other available scientific information we have arrived at the conclusion that there are at least some twentyfive specific conditions or requirements which have to be fulfilled in order for life as we know it to appear and evolve in a planetary system such as ours. Most of these necessary conditions or requirements are mutually interdependent, but in order to discuss their role in depth they have been divided into five major general areas which are discussed in some detail herein. Planetary criteria, which relate to the physical properties of the planet as it is formed and as it becomes a differentiated cosmic body and potential abode of life. The mass, orbital characteristics and energetic relationships with the central star as well as the discrete separation of gas, liquid and solid phases of the planet are of utmost importance. Chemical criteria, which are concerned with the composition, availability of effective energy sources, and chemical constraints (solvent, pH range, redox potential) of the environment(s) where reactions take place for the prebiological formation of biochemical compounds. Protobiological criteria, which relate to the prebiologically synthesized oligomeric and polymeric biomolecules, how they interact cooperatively to form protobiological structures and functions (replication, catalysis, information transfer, etc.) and self-assemble to give rise to a living system. Evolutionary criteria, which are concerned with the processes responsible for the increase in complexity of organisms by genomic multiplication, symbiotic integration and cellular differentiation, as well as with the negentropic ability of organisms to continuously recycle all the volatile biogenic elements. Altogether these processes made possible the development and evolution of life from the simplest prokaryotic cell ancestor to a cognitive and manipulative multicellular organism (man). In order to extend this inquiry to other systems beyond our solar system a fifth set of requirements based on astronomical observations is also discussed, namely, the Stellar criteria, which relate to the elemental composition mass, lifetime, and other features of Main Sequence stars which may be surrounded by planetary systems similar to our own. Finally, a brief review is made on the probability of the existence of extraterrestrial life as well as of civilizations capable of interstellar communication in our Galaxy.

Origin of organic compounds on the primitive earth and in meteorites

The role and relative contributions of different forms of energy to the synthesis of amino acids and other organic compounds on the primitive earth, in the parent bodies or carbonaceous chondrites, and in the solar nebula are examined. A single source of energy or a single process would not account for all the organic compounds synthesized in the solar system. Electric discharges appear to produce amino acids more efficiently than other sources of energy and the composition of the synthesized amino acids is qualitatively similar to those found in the Murchison meteorite. Ultraviolet light is also likely to have played a major role in prebiotic synthesis. Although the energy in the sun's spectrum that can be absorbed by the major constituents of the primitive atmosphere is not large, reactive trace components such as H2S and formaldehyde absorb at longer wavelengths where greater amounts of energy are available and produce amino acids by reactions involving hot hydrogen atoms. The thermal reaction of CO + H2 + NH3 on Fischer-Tropsch catalysts generates intermediates that lead to amino acids and other organic compounds that have been found in meteorites. However, this synthesis appears to be less efficient than electric discharges and to require a special set of reaction conditions. It should be emphasized that after the reactive organic intermediates are generated by the above processes, the subsequent reactions which produce the more complete biochemical compounds are low temperature homogenous reactions occurring in an aqueous environment.