Geological Time Scale

Geologic Time Scale

A system that organizes major stages in Earth's history over more than 4.6 billion years, defined by fossil succession,  constructed in the 19th century by William Smith

Eon

largest division of unit

Era

subdivision of eons

Period

Fundamental time intervals associated with distinct fossil clues.

Epoch

Subdivisions of periods, characterized by major landscape changes and climate shifts.

Devonian Period

“Devonshire, England,” when insects moved onto land

approximately 90%

Amount of Earth’s geological history that Precambrian Eons take up

Hadean Eon

Earth formed by an accretion disc of space debris; mostly a harsh, molten surface.

Archaean Eon

Earth's crust finally solidifies and cools; the emergence of the very first simple life forms.

Proterozoic Eon

Single-celled organisms evolve into primitive photosynthetic bacteria.

Phanerozoic Eon

Derived from the Greek term for “visible life,” abundant fossils were unearthed in the rocks and deposits in the Phanerozoic eon

Paleozoic Era

The first and longest era of the Phanerozoic Eon

Green algae

what plants evolved from in the ocean

Ordovician Period

When plants moved onto land

Amphibians

what developed 50 million years later after the Devonian Period

Carboniferous Period

when trees and reptiles had developed, associated with coal-bearing rocks

Paleozoic Era Timeline

Marine life → Land plants → Insects → Amphibians → Reptiles

Mesozoic Era

also known as the “Age of Dinosaurs,”

Triassic Period

Dinosaurs and mammals evolved

Jurassic Period

Birds evolved from dinosaurs

Late Jurassic - early cretaceous

when cone-bearing plants evolved

Mesozoic Era Timeline

reptile ancestors → dinosaurs and mammals → birds

Cenozoic Era

“Age of mammals,” covers the last 66 million years. Also when the flowering plants expanded

Paleogene Epoch

when the earliest primates evolved

Late Neogene Period

when the genus homo evolved

How we name periods:

1. Location where rocks of that age were first described

2. Rocks or rock characteristics

Mass Extinction

Large number of species disappear over a relatively short period of geologic time. The phanerozoic eon experienced five major mass extinctions.

Permian Mass Extinction

largest mass extinction, there were changes in fossil records and evidence for boundaries in the geologic time scale

Glaciation Escalator

Early Eocene, Oligocene, Miocene, Pleistocene

Early Eocene Epoch

the Earth was very warm

Oligocene Epoch

Glaciers first appear in Antarctica

Miocene Epoch

Glaciers appear in Greenland

Pleistocene Epoch

covers much of North America and Europe, ended 11,700 years ago