Phanerozoic vs. Precambrian — What's the Difference?

The Phanerozoic Eon is the current geologic eon in the geologic time scale, and the one during which abundant animal and plant life has existed. It covers 538.8 million years to the present, and it began with the Cambrian Period when animals first developed hard shells preserved in the fossil record.

The Precambrian (or Pre-Cambrian, sometimes abbreviated pꞒ, or Cryptozoic) is the earliest part of Earth's history, set before the current Phanerozoic Eon. The Precambrian is so named because it preceded the Cambrian, the first period of the Phanerozoic Eon, which is named after Cambria, the Latinised name for Wales, where rocks from this age were first studied.

Of, relating to, or being the geologic time period from approximately 542 million years ago to the present, comprising the Paleozoic, Mesozoic, and Cenozoic Eras, and marked by an abundance of fossil evidence of life, especially higher forms, in the corresponding rocks. See Table at geologic time.

Of, relating to, or being the geologic time period between Hadean Time and the Cambrian Period, often subdivided into the Archean and Proterozoic Eras, comprising most of the earth's history and marked by the appearance of primitive forms of life. See Table at geologic time.

The Phanerozoic Eon.

The Precambrian Eon.

Alternative form of Phanerozoic

The eon following the Hadean time and preceding the Phanerozoic eon; from about 3,800 million years ago until 544 million years ago

The period from about 5,400 million years ago until the present