This time period ranged from 4600 - 541 million years ago.

The Precambrian (or Pre-Cambrian) is the large span of time in Earth's history before the current Phanerozoic Eon, and is a Supereon divided into several eons of the geologic time scale. It spans from the formation of Earth about 4600 million years ago (Ma) to the beginning of the Cambrian Period, about 541.0 ± 1.0 Ma, when macroscopic hard-shelled animals first appeared in abundance. The Precambrian is so named because it precedes the Cambrian, the first period of the Phanerozoic Eon, which is named after Cambria, the classical name for Wales, where rocks from this age were first studied. The Precambrian accounts for 88% of geologic time.

THE

INTRODUCTION TO

Trilobites are a well-known fossil group of extinct marine arthropods that form the class Trilobita. Trilobites form one of the earliest known groups of arthropods.

1

PRECAMBRIAN