SESSION I. DISCUSSION 115 



theory describing the thermal history of the Earth but, to satisfy these conditions, it is 

 not necessary to proceed from the assumption that the Earth began by being molten. 

 One may proceed on the basis of a theory that the Earth was not molten and was relatively 

 cold, e.g. that of Schmidt. 



Let us return to the facts. The question of natural radioactivity has now been fairly 

 well studied by physicists. There are methods whereby the presence of radioactivity may 

 be measured with extreme accuracy. Many measurements of radioactivity, both of ter- 

 restrial formations and of meteorites arriving from space, show that, as a rule, radioactivity 

 is present in all formations. Radioactive elements are dispersed. The amount of radio- 

 active material is extremely small, from i to o-oi ppm. However, if these fractions of a 

 gram are considered over thousands of millions of years, they could have heated the 

 depths of the interior of the Earth to some thousands of degrees. 



Goldschmidt's concepts that the atoms of uraniimi and thorium have too great a 

 volimie to enter into any silicate lattice during crystaUization should, it seems, now be 

 reconsidered. Studies of the structure of olivine, a basic component of the Earth show 

 that its structure contains a sufficient number of large holes to accommodate foreign 

 atoms. [This work was carried out by Belov and his colleagues at the Institute of Crystallo- 

 graphy of the Academy of Sciences of the U.S.S.R.] Therefore we cannot beheve that 

 the radioactive atoms are concentrated in the Earth's crust only. They may be widespread 

 over the silicate mantle of the Earth. 



Furthermore, the radioactivity of ^''K has been investigated during the last decade. 

 This is known not to be a rare element but to be widely distributed in nature. The heat 

 given out by the breakdown of potassium played a considerable part in the history of the 

 Earth. Most contemporary students of the thermal history of the Earth (Verbogen, Birch, 

 Jacobs, Allan) consider that there is no reason to suppose that radioactive sources of 

 heat are completely absent at a great depth within the Earth and believe them to be one 

 of the main sources of its heat. They gradually heated the deepest parts of the interior 

 of the Earth without making any associated change in the mean annual temperature of the 

 surface. Our calculations, based on the assumption that the mean composition of the 

 Earth corresponds with the mean composition of stony and iron meteorites, show that 

 the Earth as a whole has never been molten. However, beneath the crust of the Earth 

 the conditions are suitable for the formation of molten foci which might be associated 

 with volcanic activity. In the past the layer in which molten foci could be formed was 

 considerably nearer the surface than it is now and volcanic activity was greater. 



Outflows of lava enabled the continents to extend. This concept is confirmed by the 

 works of Rubey, Wilson, Magnitskii and Vinogradov. The vapours given off during 

 eruptions condensed to water. 



While this was happening the mean temperature of the surface remained much what 

 it is now and this, it would seem, must have been more favourable for the emergence of 

 life than the extremely high temperatures entailed by the hypothesis that the Earth was 

 originally molten. 



V. V. Alpatov (U.S.S.R.): 



I should like to draw special attention to the problem of the optical activity of proto- 

 plasm and its components in connection with the origin of life on the Earth. Pasteur 

 made one of the most outstanding discoveries of the last century in the biological field. 

 He demonstrated a fundamental molecular difference between living and non-Hving 

 matter, namely, the inequality of the number of molecules of the dextro and laevo forms 

 in materials derived from organisms. This dissymmetry of Ufe is not only expressed at 

 the molecular level, it also manifests itself in the structure of the bodies of plants and 

 animals. My experiments, published over the past decade in Dokl. Akad. Nauk S.S.S.R., 

 give reason for the beHef that the dissymmetry of the form of the bodies of organisms is 

 closely associated with the dissymmetry of the molecules of which they are composed. 

 It is interesting to consider the distribution over the surface of the globe of populations 

 of right-handed and left-handed organisms. I shall adduce only two examples from my 

 own personal experiments. Among the colonies of the bactmum Bacillus mycoides, which 



