74 The Sea 
THE EARTH COOLS OFF 
Whether or not the earth was born from the sun, it is evi- — 
dent that its early history was a hot one. At one time (three 
to four billion years ago) it was in a molten state. Harold 
Jeffreys, British mathematical physicist, estimates that it 
took about 15,000 years before the molten mass began to 
solidify. The heavier portions settled toward the center of 
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the earth, and the lighter parts remained floating upon the ~ 
surface to form our present day crust. 
Most of the light gases that were present in the outer por- 
tions of the earth while still in the molten state were prob- 
ably lost to outer space. That means that our present day at- ‘ 
mosphere and ocean may not be the same as the primitive — 
gas and water vapor that covered the young earth. Much of 
the original water vapor of the earth must have gone into the 
formation of igneous rocks. Silica and water are supposed to 
be miscible at high temperatures, according to Dr. Harold — 
Jeffreys. This amazing fact means that, when heated het 
enough, rock and water will mix in all proportions. 
The present day ocean and atmosphere are supposed to 
have been formed by the excessive volcanic action of these : 
early times. Water vapor and carbon dioxide are plentiful in — 
volcanic gases. The water vapor condensed to form the 
oceans and the atmosphere was largely carbon dioxide. The — 
oldest Pre-Cambrian granites are supposed to be about one 
and one half billion years old, the age being determined by 
the extent of decay of certain radioactive elements present 
in the rocks. The earliest forms of life appeared about one 
billion years ago. Eventually the plants converted most of 
the carbon dioxide of the atmosphere to oxygen, and the 
