THE LIFELESS EARTH 25 



published his famous Discours sur Ics Revolutions de la Surface 

 du Globe, the past history of the earth, of its waters, of the 

 atmosphere, and of the sun — the four great complexes of in- 

 organic environment — has been written with some approach to 

 precision. Astronomy, physics, chemistry, geology, and pa- 

 laeontology have each pursued their respective lines of obser- 

 vation, resulting in some concordance and much discordance 

 of opinion and theory. In general we shall find that opinion 

 founded upon life data has not agreed with opinion founded 

 upon physical or chemical data, arousing discord, especially in 

 connection with the problems of the age of the earth and the 

 stability of the earth's surface. 



In our review of these matters we may glance at opinions, 

 whatever their source, but our narrative of the chemical origin 

 and history of life on the earth will be followed by observations 

 on living matter mainly as it is revealed in palaeontology and 

 as it exists to-day, rather than on hypotheses and speculations 

 upon pre-existing states. 



The formation of the earth's surface is a prelude to our 

 considering the first stage of the environment of life. Accord- 

 ing to the planetesimal theory, as set forth by Chamberlin,^ the 

 earth, instead of consisting of a primitive molten globe as pos- 

 tulated by the old nebular hypothesis of Laplace, originated in 

 a nebulous knot of solid matter as a nucleus of growth which 

 was fed by the infall or accretion of scattered nebulous matter 

 (planetesimals) coming within the sphere of control of this 

 knot. The temperature of these accretions to the early earth 

 could scarcely have been high, and the mode of addition of 

 these planetesimals one by one explains the very heterogeneous 

 matter and differentiated specific gravity of the continents and 

 oceanic basins. The present form of the earth's surface is the 



' Chamberlin, Thomas Chrowder, igi6. 



