Cryptozoic EonCryptozoic Eon

Some geologists subdivide the Cryptozoic Eon into the Archean and Proterozoic Eras. This arrangement is based primarily on the distinguishing characteristic shown in the box below.

The prefix crypto- comes from the Greek word for “hidden”, referring to the fact that very few fossil remains are found in Cryptozoic rocks. For reasons that will become apparent in the following discussion, the entire Cryptozoic Eon is commonly referred

to as the pre-Cambrian..

Proterozoic EraProterozoic Era2.5 billion to 550 million years ago

Distinguishing characteristic: shallow-water marine life forms

Archean EraArchean Era 4.5 to 2.5 billion years ago

Distinguishing characteristic: no large continents exist

Phanerozoic EonPhanerozoic Eon

The prefix phanero- comes from the Greek word meaning “apparent” and refers to the abundant fossil remains found in these rocks. Historically, the dividing line

between the Cryptozoic and Phanerozoic eons has been placed at the first appearance of abundant fossil remains about 550M years ago. As a result, the

Phanerozoic Eon represents the last 550M years of Earth history.

For reasons that will become apparent in the following discussion, the entire Cryptozoic Eon is commonly referred to as the pre-Cambrian.

Avoid term confusion!

Geologists Technical Term = Cryptozoic Eon

Commonly Used Term = pre-Cambrian

Cryptozoic Eon = pre-Cambrian