CHAPTEK XI. 
THE OCEAN IN WHICH WE LIVE. 
The foregoing chapters have treated briefly of 
the earth as a molten globe, its gradually forming 
crust of rock strata, and of the plants and animals 
that followed in successive ages. But that is not all 
there is of our globe. It is surrounded by an en¬ 
velope of air which is called the atmosphere; an 
envelope practically not over fifty miles deep, al¬ 
though atmospheric gases in a rarefied form may float 
out from the earth for a distance of two hundred 
miles. 
In pre-Archaean times the atmosphere was prob¬ 
ably more than a thousand miles deep ; but in the 
succeeding ages a great part of the vapors settled and 
formed oceans ; the gases were absorbed until there is 
nothing left but oxygen and nitrogen. If the moon 
is to be taken as an example, not only the waters on 
the earth’s surface but also the atmosphere will be 
gradually absorbed by the globe, so that at some time 
there will be no water and no air on this earth. 
Animal and vegetable life will have passed away and 
the earth will be dead indeed. But this will not hap¬ 
pen, if it does at all, for at least millions of years 
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