Geologic Time Scale Overview

Fill-in-the-blank flashcards covering eons, eras, periods, and key dates of the geologic time scale.

The four eons of Earth's history from oldest to youngest are ___, ___, ___, and ___.

Hadean, Archean, Proterozoic, Phanerozoic

The Precambrian includes the ___, ___, and ___ eons.

Hadean, Archean, Proterozoic

The eon that begins at 0.54 Ga (541 Ma) is the ___.

Phanerozoic

Earth originally formed during the ___ Eon.

Hadean

The three eras of the Phanerozoic Eon in order are ___, ___, and ___.

Paleozoic, Mesozoic, Cenozoic

The era that immediately follows the Proterozoic Eon is the ___ Era.

Paleozoic

The era that comes after the Paleozoic is the ___ Era.

Mesozoic

We are currently living in the ___ Era.

Cenozoic

The periods of the Paleozoic Era in order are ___, ___, ___, ___, ___, and ___.

Cambrian, Ordovician, Silurian, Devonian, Carboniferous, Permian

The period that comes after the Cambrian is the ___.

Ordovician

The period that comes immediately before the Devonian is the ___.

Silurian

The ___ Period directly precedes (comes right before) the Mesozoic Era.

Permian

The periods of the Mesozoic Era in order are ___, ___, and ___.

Triassic, Jurassic, Cretaceous

The period that follows the Triassic is the ___.

Jurassic

The period that directly precedes the Cretaceous is the ___.

Jurassic

The ___ Period ends the Mesozoic Era.

Cretaceous

The periods of the Cenozoic Era in order are ___, ___, and ___.

Paleogene, Neogene, Quaternary

The period that comes after the Paleogene is the ___.

Neogene

We are currently in the ___ Period of the Cenozoic.

Quaternary

Earth formed approximately ___ billion years ago during the Hadean.

4.6

The Proterozoic Eon began about ___ billion years ago.

2.5

The Phanerozoic Eon began about ___ million years ago.

541

The Cambrian Period began about ___ million years ago.

541

The Ordovician Period began about ___ million years ago.

485

The Silurian Period began about ___ million years ago.

445

The Devonian Period began about ___ million years ago.

419

The Carboniferous Period began about ___ million years ago.

359

The Permian Period began about ___ million years ago.

300

The Triassic Period began about ___ million years ago.

252

The Jurassic Period began about ___ million years ago.

201

The Cretaceous Period began about ___ million years ago.

145

The Paleogene Period began about ___ million years ago.

66

The Neogene Period began about ___ million years ago.

23

The Quaternary Period began about ___ million years ago.

2.6

"Precambrian" is ___ an official era (official/unofficial).

unofficial

The two named periods in the Neoproterozoic part of the Precambrian are the ___ and the ___.

Cryogenian, Ediacaran

The event that marks the end of the Precambrian is the start of the ___ Period, also called the ___.

Cambrian, Cambrian Explosion