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The Precambrian Era lasted for 4 billion years. It is the longest period in Earth's history. It consists of the Archaean eon and the Proterozoic eon. At the end of the Precambrian (the Proterozoic) life began to appear and to evolve. But the fossils from most of the Precambrian era are very few in number and very rare, so little is known about life on Earth at that time still.