Library: Geology by Credo Reference: History of Earth

Geological Eras

Cenozoic Era: Topic Page
Last major division of geologic time lasting from 65 million years ago to the present. The Cenozoic is divided into the Tertiary (from 65 million years ago until 2 million years ago) and Quaternary (2 million years ago to the present) periods.
Mesozoic Era: Topic Page
[Gr.,=middle life], major division of geologic time (see Geologic Timescale, table) from 65 to 225 million years ago. Great crustal disturbances that marked the close of the Paleozoic and the beginning of the Mesozoic eras brought about drastic changes in the topography of North America.
Paleozoic Era
From The Columbia Encyclopedia
Paleozoic era (pā´´lēәzō´ĭk), a major division (era) of geologic time occurring between 570 to 240 million years ago. It is subdivided into six periods, the Cambrian, Ordovician, Silurian, Devonian, Carboniferous, and Permian.
Precambrian: Topic Page
Name of a major division of geologic time from c.5 billion to 570 million years ago. It is now usually divided into the Archean and Proterozoic eons. Precambrian time includes 80% of the earth's history.
Archean Eon
From Britannica concise encyclopedia
Older of the two divisions of Precambrian time. The Archean begins with the formation of the Earth's crust 4 billion years ago and extends to 2.5 billion years ago.
Proterozoic Eon
From Britannica concise encyclopedia
Younger of the two divisions of Precambrian time, from 2.5 billion to 542 million years ago.

Cambrian Period: Topic Page
The earliest geological period of the Palaeozoic era, lasting from c.590 to 505 million years ago.
Carboniferous Period: Topic Page
Fifth period of the Paleozoic era of geologic time, from 350 to 290 million years ago.
Cretaceous Period: Topic Page
The Cretaceous is the last period of the Mesozoic. It lasted for approximately 80 million years, ending 65 million years ago.
Devonian Period: Topic Page
Fourth period of the Paleozoic era of geologic time between 408 and 360 million years ago.
Jurassic Period: Topic Page
A geological period of the Mesozoic era extending from c.213 to 144 million years ago.
Ordovician Period: Topic Page
The second of the geological periods of the Palaeozoic era, extending from c.505 to 438 million years ago.
Permian Period: Topic Page
A geological period of the Upper Palaeozoic era, extending from c.286 to 250 million years ago.
Silurian Period: Topic Page
The third of the geological periods of the Palaeozoic era, extending from c.435 to 408 million years ago.
Triassic Period: Topic Page
A period of geological time during the early Mesozoic era, lasting from about 240 to 200 million years ago.