Ocean
Collier's New Encyclopedia (1921)
the sea, using that term in its widest sense. Properly speaking, there is but one ocean or sea, all the salt water on the globe, with a few trifling exceptions like the Caspian, the Sea of Aral, and the Dead Sea, being more or less in complete communication with each other. Different portions of the ocean have received distinctive names. The Arctic, the Atlantic, the Indian, the Pacific, and the Antarctic oceans, five in all; or if the Atlantic and Pacific be separated into a N. and a S. portion by the equator, then there are seven in all. The unequal heating of portions of the vast expanse of water on the globe, the rotation of the earth, and other causes tend to keep the water in constant circulation and preserve it from being stagnant and impure. The attractions of the moon and sun cause tides. The area of the ocean is about 155,000,000 square miles, or nearly three-fourths of the whole surface of the earth. This space is distributed (in square miles) among the principal seas as follows: Arctic, 5,000,000; Antarctic, 10,000,000; Indian, 20,000,000; Atlantic, 40,000,000; Pacific, 80,000,000. This gre great volume of water largely modmod ifies the temperature of the adjacent lands, tempering the heat of summer and the cold of winter. As far as observation has yet extended, the average depth of the ocean is somewhat above two miles. At 62° F., the relative density of salt and fresh water is as 1.0275 to 1. The ocean has been salt through all known geological periods. The origin of this saltness is a difficult geological problem. While on land the temperature rises as mines or borings become deeper, the opposite occurs with the ocean. As a rule, the surface water is the warmest. The level of the ocean remains permanent from age to age. It is the land that is upheaved or subsides.
What Has Changed in the Last Century
Collier's 1921 statement that "the level of the ocean remains permanent from age to age. It is the land that is upheaved or subsides" is the line that has aged worst: global mean sea level has risen roughly 20 cm (8 inches) since 1900 and is now climbing over 3 mm a year as ice sheets melt and the warming water expands. The 1921 guess at average depth, "somewhat above two miles," stands up well against the modern figure of about 3,700 m; the deepest point, the Challenger Deep at nearly 11,000 m, was first reached by men in the bathyscaphe Trieste in 1960. What Collier's could not imagine was the floor itself, revealed from the 1950s onward as a globe-circling system of mid-ocean ridges where new crust is made — the evidence that established plate tectonics and explained why the basins change shape over geological time. The "difficult geological problem" of saltness is now routine chemistry (rock weathering plus volcanic and hydrothermal input), and a new worry has replaced it: the ocean has absorbed enough carbon dioxide to measurably acidify its surface waters, and has taken up the great majority of the excess heat trapped by greenhouse gases.
Written for this edition, 2026.