from the book, "Petrified Lightning"
About three billion years ago, after more than one and one—half billion years of cooling down, the earth became blanketed with a dense cloud that included much hydrogen and oxygen. The cooling persisted until the gases that surrounded it condensed into water and fell as rain. The downpour continued unabated for about 60,000 years, filling ocean basins and lowlands with an estimated 326 million cubic miles of water. And no matter how much is used, polluted, or wasted, the earth retains all of the water ever created.
At present over 70 percent of the earth's surface is covered by water, 97 percent of which is contained in the oceans. Of the remaining 3 percent that is freshwater, over 2 percent is held in ice caps and glaciers in high mountains, and less than 1 percent is in reserves below the earth's surface, in the atmosphere, and in rivers, lakes, and inland seas.
Most of the world's great river systems, from the Amazon to the Ganges, the Rhone to the Columbia, originated in glaciers. Nearly three—fourths of all the freshwater in the world, just under seven million cubic miles, is stored in the form of glacial ice. Authorities estimate that this reserve is the equivalent of about 60 years of rainfall over the entire globe.
Greenland and Antarctica alone are capped by five million cubic miles of ice. If global warming proceeds as predicted, this ice will gradually melt, causing the sea level to rise nearly 300 feet worldwide and adding to the percentage of saltwater. And coastal cities such as Boston and New York will be visited only by persons in scuba gear or on a submarine.
During the ice age that ended 10,000 years ago, over 30 percent of the land surface was covered by ice sheets thousands of feet thick. This moving glacial ice constantly supplied the coastal seas with gigantic icebergs. Then, as now, when the ice moved from the land into the sea, these enormous chunks of ice would break off, a process called calving. They float away from the shore, and thus are born icebergs. Considering that so much ice covered the lands during the last ice age, the northern seas must have been heavily dotted with massive icebergs. These ice age icebergs may have reached as far south as the latitude of Mexico City, well within the Torrid Zone. This would indicate that the oceans maintained a rather frigid temperature.
Since ice is so heavy and solid, observers of icebergs, and of ice cubes hugging the surface of cool drinks, wonder just why ice floats on the very water from which it came. The behavior of water as it cools toward the freezing point is amazing. Almost all materials contract as they cool, reaching their greatest density at freezing. Not so with water! It contracts as it cools down, but only to 4 degrees centigrade; at this point it begins to expand until it freezes at 0 degrees. Because expansion decreases its density, the ice that results takes more space than the water from which it came.
A particular volume of ice is lighter than an equal volume of water. A cubic foot of water weighs 62.5 pounds; a cubic foot of ice weighs 56.9 pounds, a difference of about 5.5 pounds. As do all lighter substances, the lighter ice will float on the heavier water. Moreover, since the ice consists of freshwater (which is lighter than seawater) the icebergs float partly above the surface.
The physical change of water into ice creates a force so powerful that water pipes break, car radiators crack, carbonated beverages explode, and caps on bottles of frozen milk sit on an ice tower several inches high. Great chunks of rock come tumbling down mountainsides, split off by the expansion of freezing water between the cracks in the bedded rock (a process known as frost wedging). The result of this characteristic of water is that lakes and rivers freeze at the surface instead of from the bottom up. The living creatures remain comfortable in the relatively warm waters, even when the surface of the lake or river is frozen solid. This fact accounts for all aquatic survival, perhaps all life!
Another important property of water is its ability to absorb free oxygen; this increases as the water temperature decreases. One would assume that warm tropical waters are the home of most sea animals, just as tropical forests are more densely populated than polar regions. Actually cold waters contain the most abundant sea life because cold water tends to hold more oxygen than warm. In fact the solubility of oxygen in water at 0 degrees centigrade is approximately twice that of water at 30 degrees; for this reason, marine life becomes more abundant as seawater gets colder. Surveys show that sea animal populations increase greatly toward the poles and lessen near the equator. Exceptions occur where upwellings of cold water exist.
The photographs one often sees of a warmly dressed angler fishing through a hole bored in the ice, with a large catch of fish sitting alongside, are usually not fabricated. The fish beneath the ice are hungry and very energetic. Invigorated by waters abundant in dissolved oxygen, they are always ready for the next meal.