Scientists believe the Earth was formed about four billion years ago. Within its primitive atmosphere were the basic elements needed to form water. As the Earth cooled from a mass of molten rock, water formed in the atmosphere and then fell to the ground in a rain that lasted for many years, forming the oceans.
Ever since the formation of the oceans, water has been wearing the Earth into a smooth surface with its flowing and rubbing actions. If other forces on the planet were not counteracting these actions by constantly raising up new hills and mountains, the planet would eventually become one vast, shallow ocean.
The flow of water flattens mountains and cuts canyons deep into the surface of the earth. It hollows out underground caverns and leaves behind attractive formations. Water creates soil by breaking down rocks and
FIGURE 1.2
Distribution of water on Earth's surface
SOURCE: "Distribution of Water on Earth's Surface," in National Water Quality Inventory—1996 Report to Congress, U.S. Environmental Protection Agency, 1998
organic material and depositing it elsewhere. Water in the form of ice redesigned the face of the earth as glaciers advanced and receded many thousands of years ago. The slow, relentless processes of water freezing, melting, flowing, and evaporating will likely make the Earth's appearance as different a million years from today as it was a million years ago.
User Comments Add a comment…