142 ANNUAL REPORT SMITHSONIAN INSTITUTION, 1946 
gether the cosmic-minded geologist and the astronomer. For it means 
that the rocky surface of the earth is essentially coeval with the plane- 
tary system. The measurement of the ages of the oldest rocks is 
therefore a measurement also of the total duration of the earth. The 
astronomer sees little support for the suggestion that all the planets 
may have not been born together. Planetary birth is probably such a 
catastrophic affair that if a second family were produced the violence 
would wreck all preexisting systems of planets and satellites. 
We owe the concept and analysis of the high-speed cooling of the 
original surface of a disruption-produced earth to Harold Jeffreys, 
whose attack on cosmogony has been from the standpoint of geo- 
physics. 
It is worth emphasizing again that the earth is a sidereal body of 
really great antiquity. We shall see later that there is good evidence 
for believing that the pre-Cambrian rocks of our countryside have 
existed, many of them unchanged, throughout most of the history of 
the Pleiades, the Milky Way, and the expanding universe. And it 
is additional good fortune that during the past thousand million years 
there has been left a fairly continuous record of living forms on this 
ancient crust; that continuity of organisms, and especially the char- 
acteristics of plant forms for two or three hundred million years, 
provides the astronomer with his best evidence on the stability of re- 
mote stars. Indeed, the fossil plants, in the sediments dated by radio- 
active processes, have inspired and practically forced our search for 
heat-generating atomic transformations within the stars.° These 
fossils prove the essential constancy of the intensity and quality of 
solar radiation throughout geological time. Many fertile and suc- 
cessful astronomical theories would probably still remain unformu- 
lated if, instead of the paleontological record of the earth’s surface, 
we had a dictum dating organisms, for instance, from only 4000 
B. C. 
NOTE ON SEVERAL COSMOGONIC FAILURES 
The astronomers and geologists who have worked assiduously dur- 
ing the past half century on the theory of the origin of the earth have 
reason to be sincerely satisfied with themselves because they have 
produced so many hypotheses that do not work. By showing what is 
not so, not sufficient, not compatible with the growing body of verifi- 
able observations, they have cleared the field for more competent 
theoretical investigations and indicated in what direction profitable 
astronomical and mathematical researches may lie. 
A serious hindrance to the formulation of any planetary-system 
cosmogony that may be even temporarily successful is the abundance 
® Shapley, H., The age of the earth, Publ. Astron. Soc. Pacific, October 1918. 
