Table of Geological Periods

Modern science generally accepts that planets are formed by the accretion of gas and dust in a cosmic cloud with no way of really estimating the length of this process. Our Earth acquired its present size, more or less, between 4 billion and 5 billion years ago. Life on Earth originated about 2 billion years ago, but there are no good fossil remains from periods earlier than the Cambrian, which began about 490 million years ago.
The known geological history of Earth from the Precambrian on is subdivided into three eras. These in turn are divided into a number of periods. They, in turn, are subdivided into epochs and stage ages. Many of the epochs are especially well known because of rich fossil finds.

New Geological Period

In 2004 geologists added a new time period to Earth's chronology called the Ediacaran Period which lasted for about 50 million years, from 600 million years ago to about 542 million years ago. It was the last period of the Precambrian's Neoproterozoic Era and multicellar organisms first appeared during this time.

Precambrian Time

The Precambrian's lower limit or beginning is not defined, but it ended about 542 million years ago. The Precambrian encompasses about 90% of Earth's history.

Eonothem Eon	Duration	Eras	Events
Archaean	@ 2,500? Million years	Eoarchean Paleoarchean Mesoarchean Neoarchean	Formation of oceans and atmosphere Bacteria develop

Paleozoic Era

Period	Duration	Epochs	Events
Cambrian	@ 54 Million Years	Lower Cambrian Middle Cambrian Upper Cambrian	Invertebrate sea life proliferate during this and the following
Ordovician	@ 45 Million Years	Lower Ordovician Upper Ordovician	Diverse marine life, including vertebrates Vascular plants also begin their development
Silurian	@ 28 Million Years	Lower Silurian Upper Silurian	Coral Reefs Giant Scorpions Early Jawed Fish
Devonian	@ 57 Million Years	Lower Devonian Upper Devonian	Numerous fishes, other sea life Many plants including first trees Wingless insects
Carboniferous	@ 60 Million Years	Upper, Middle, and Lower Mississippian Upper, Middle, and Lower Pennsylvanian	Maximum coal formation in swampy forests Insects, amphibians, reptiles, fishes, clams, crustaceans

Mesozoic Era

The Mesozoic Era began about 251 million years ago and lasted about 186 million years. This is the so-called “Age of Reptiles”

Period	Duration	Epochs	Events
Triassic	@ 51 Million Years	Lower Triassic Middle Triassic Upper Triassic	Early dinosaurs, crocodiles, turtles First mammals
Jurassic	@ 54 Million Years	Lower Jurassic Middle Jurassic Upper Jurassic	Many seagoing reptiles Early large dinosaurs Flying reptiles (pterosaurs) Earliest known birds
Cretaceous	@ 80 Million Years	Lower Cretaceous Upper Cretaceous	Dinosaurs and other reptiles dominate Seed-bearing plants appear

Cenozoic Era

The Cenozoic Era began about 66 million years ago and includes the geological present. This is the so called “Age of Mammals”

Period	Duration	Epochs	Events
Paleogene	@ 42 Million Years	Paleocene Eocene Oligocene	Rich insect fauna Early bats Many mammal and bird species
Neogene	@ 23 Million Years	Pliocene Pleistocene Holocene - the last 10,000 years to the present.	Further development of mammals and birds Various forms of humans, including Homo sapiens