Precambrian Time
Precambrian Time, a major division of geologic time. Precambrian time began approximately 4,600,000,000 years ago with the formation of the earth and ended about 570,000,000 years ago with the beginning of the Cambrian Period, the first period of the Paleozoic Era. On each continent there is a large, stable, low-lying region, called a shield, that is composed mostly of rock formed during Precambrian time. Precambrian rocks contain important deposits of ores of various metals, including iron, gold, nickel, and uranium.
Life on earth first appeared during Precambrian time. The detection and study of the record of Precambrian life is difficult, because living things with parts that readily fossilize did not appear until the Cambrian Period. Nevertheless, traces of single-celled organisms have been found in rock more than 3,000,000,000 years old. By the end of Precambrian time, multicelled organisms had developed.