Presently, there are eight major plates. Earth is 4.5 to 4.6 billion years old, but the oldest known rocks are about four billion years old. Rocks older than three billion years are rare. The oldest fossils of living organisms are less than 3.9 billion years old. Seventy-one percent of Earth's surface is covered with water.
Earth is the only planet on which water can exist in a liquid form on the surface.
The heat capacity of the oceans keeps Earth's temperature stable. Liquid water is also responsible for most of the erosion and weathering of Earth's continents. The tiny amount of carbon dioxide in the atmosphere maintains Earth's surface temperature because of the greenhouse effect. Without this, the oceans would freeze. The interaction of Earth and the Moon slows Earth's rotation by about two milliseconds per century.