CHAPTER XVI
THE EARTH
A Planet at Close Range
Diameter—7927 miles
Volumes could not cover the extremely complex history of the earth, nor picture with justice the exquisite construction of even its smallest features. It is here that the astronomer puts away his glass and turns detective with the geologist on his own home ground.
Astronomers, basing their computations of the earth's age upon the rate at which the sun is shrinking or contracting, have placed it at 25,000,000 years, but geologists claim that this is too short a time to account for the enormous thickness of stratified deposits, the salinity of the ocean, and other similar evidence which seems to prove that it is probably 100,000,000 years old, or even older. Later estimates based upon other modes of production of solar heat may extend this estimate several hundred fold.
The moon is believed by some to have once been a part of the earth and that it was formed through a division of the earth's ball when our world was in an early stage of evolution. Becoming two separated bodies, they have remained bound together by mutual attraction, and thus move around the sun.
According to the Nebular Hypothesis expounded by La Place, the earth and moon once shone like stars but, through the long ages of time they have gradually cooled, and, their lights extinguished, two cold-surfaced globes now wend their way around the sun. The smaller of these two globes is now scarred and old but
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