THE ORIGIN AND DEVELOPMENT OF THE EARTH 103 
of more than 5,600,000,000 miles. "This ball of gas, which 
supposedly contained all of the material in the solar system 
today, possessed at its beginning a very high temperature 
which it immediately began to lose, just as any hot object will 
lose its heat. This loss of heat caused shrinkage of the mass, 
and therefore increased rapidity of rotation. In the course 
of this rotation great rings of gas, one ring for each of the 
planets, were left by the contracting central mass. These 
rings, it is supposed, resembled those about the planet Sat- 
urn—in fact it is quite probable that the Saturnian rings sug- 
ested this part of the hypothesis. The rings in turn broke 
up, formed spheres, and in time gave off smaller rings to be- 
come the satellites. 
According to this interpretation, the earth was originally a 
globe of very hot vapor which in the course of time cooled, 
contracted, and gave off a ring which went through the same 
process and became the moon. The parent mass continued to 
cool and shrink until it became liquid, and finally formed a 
crust over its outer surface, the interior still remaining very 
hot. At this early stage of the earth’s history the atmosphere 
contained all of the gases which now compose it, great quanti- 
ties of gases that are now united with other elements as parts 
of the rocks, and all of the hydrogen and oxgen that are now 
in the waters of the planet. When the cooling process had 
gone on for so long that gases formerly in the atmosphere 
could stay in the earth, and those falling as water could re- 
main upon it instead of passing back as vapor, the ancestors 
_of our present oceans began to form. 
The hypothesis is skilfully devised, and carefully worked 
out in many of its details. But in many respects it contains 
glaring anomalies, and many of the conditions on which it de- 
pends could never have existed. In the first place, let us con- 
sider the supposed parent nebula a little more closely. The 
total amount of matter which it contained is now in the solar 
system—no more, no less. Its diameter was, of necessity, at 
least 5,600,000,000 miles, and the original hypothesis calls for , 
an even greater figure. Dr. Moulton, of the University of 
Chicago, has comptted that in such a nebula the density 
would be only one two-hundred-forty millionth of that of air 
at sea-level—thousands of times more rarified than the most 
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