The Precambrian or Pre-Cambrian; sometimes abbreviated pЄ is the largest 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 4.6 billion years ago (Ga) to the beginning of the Cambrian Period, about 541.0 ± 1.0 million years ago (Ma), when hard-shelled creatures first appeared in abundance.