The Homologue of the Geological Record; Spectroscopic Evidence
Another source of evidence for the evolution of organisms is that derived from the study of paleontology; for the successive geological strata constitute a record of the organic forms which have successively inhabited the earth; a record which shows that in all the forms of life there is a considerable degree of continuity, and a (more or less) gradual transition from one form to another.
The homologue of this geological record in inorganic evolution is to be found in the series of stars arranged in order of decreasing temperature; for what the unknown cause of organic evolution has done for organisms, leaving the record in the geological formations, temperature (and perhaps other agencies) have done for the elements, leaving the record in stars of different heat intensities.
Lockyer has shown that the spectroscopic study of the stars, as carried on by himself and others, has revealed evidence of a very important kind for inorganic evolution. Here the results can only be briefly indicated.
As pointed out by Sir Norman Lockyer, the simplest elements appear first.
. . . In the hottest stars we are brought in the presence of a very small number of chemical elements. As we come down from the hottest stars to the cooler ones the number of spectral lines increases, and with the number of lines the number of chemical elements. . . . In the hottest stars of all we deal with a form of hydrogen which we do not know anything about here (but which we suppose to be due to the presence of a very high temperature) hydrogen as we know it, the eleveite gases, and magnesium and calcium in forms which are difficult to get here. . . . In the stars of the next lower temperature we find the existence of these substances continued in addition to the introduction of oxygen, nitrogen and carbon. In the next cooler stars we find silicium added; in the next we note the forms of iron, titanium, copper and manganese, which we can produce at the very highest temperature available in our laboratories; and it is only when we come to stars much cooler that we find the ordinary indications of iron, calcium and manganese and other metals. All these, therefore, seem to be forms produced by the running down of temperature. As certain new forms are introduced at each stage, so certain old forms disappear.[1]
The stellar evidence, like the geological record, is incomplete, because, as stated by Lockyer, of the very small range of the photographs of stellar spectra, and also because
It does not at all follow that the crucial lines of the various chemical substances will reveal themselves in that particular part of the spectrum which we can photograph.[2]
But whatever has been gleaned from the stellar evidence, though incomplete, is, like the information contained in the geological record, very significant in its indications of evolution.
