Geologic Ages
Precambrian Era

Topics covered in this section:

Introduction
Precambrian Era

Introduction

The Precambrian Era takes us all the way back to the very beginning of our planet more than 4 billion years ago.

Precambrian Era

Hadean Time

Hadean Time covers the birth of our planet, more than 4 billion years ago. There is no geologic record this old.

Archean Eon

During the Archean Eon, between 4 billion and 2.5 billion years ago, the planet's continents, atmosphere, and ocean formed. Of course, the continents were not in the same positions that they're in now.

The beginnings of life appeared in the form of one-celled organisms known as prokaryotes. These are the distant ancestors of present-day bacteria and cyanobacteria.

Proterozoic Eon

Some 2.5 billion to 570 million years ago, the atmospheric oxygen increased, allowing more complex forms of life to evolve.

Organisms, known as eukaryotes, possessed a cellular nucleus and nuclear membrane. Multi-cellular organisms made their appearance.

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