Advertisement.

EnchantedLearning.com is a user-supported site.
As a bonus, site members have access to a banner-ad-free version of the site, with print-friendly pages.
Click here to learn more.

ad
(Already a member? Click here.)


ZoomDinosaurs.com
Dinosaur and Paleontology Dictionary
A B C D E F G H I J K L M N O P Q R S T U V W X Y Z

Click on an underlined word for more information on that subject.
If the dinosaur or paleontology term you are looking for is not in the dictionary, please e-mail us.

Earth The Precambrian

The Precambrian is the geological time span that preceded the Cambrian period (before 540 million years ago). This time period comprises most of the Earth's history (roughly 7/8 of the time sime the Earth formed).

The Precambrian is defined as the time from when the Earth formed (about 4.5 billion years ago, the earliest-known rocks) until the beginning of the Cambrian period (540 million years ago). The Precambrian used to be defined as the time from when the Earth's rocks formed until the earliest life forms evolved, but as the date of the earliest fossils gets earlier and earlier, this definition has also changed.

The first life forms on Earth were simple. single-celled life forms (like blue-green (photosynthetic) algae, archaeans, and bacteria) that evolved in the seas. The earliest-known fossils are of cyanobacteria-like organisms that are roughly 3.5 billion years old. Microfossils from the Archean Eon of the Precambrian have been found in South Africa and Western Australia. The first billion years of life on Earth saw only these simple forms.

The Precambrian:
EON ERA PERIOD EPOCH PIVOTAL EVENTS
Proterozoic Eon
2.5 billion years ago to
540 mya
- Vendian Period
600 to 540 Million Years Ago
Vendian biota (Ediacara fauna), multi-celled, animals appear, including sponges. A mass extinction occurred. The continents had merged into a single supercontinent called Rodinia.
- First multicellular life: colonial algae and soft-bodied invertebrates appear. Oxygen build-up in the Mid-Proterozoic.
Archeozoic Eon
(Archean)

3.9 to 2.5 billion years ago
- - "Ancient Life" - The first life forms evolve - one celled organisms. Blue-green algae, archaeans, and bacteria appear in the sea. This begins to free oxygen into the atmosphere.
Hadean Eon
4.6 to 3.9 billion years ago
- - "Rockless Eon" - The solidifying of the Earth's continental and oceanic crusts.

For a complete timeline of geologic time, click here.


Enchanted Learning®
Over 35,000 Web Pages
Sample Pages for Prospective Subscribers, or click below

Overview of Site
What's New
Enchanted Learning Home
Monthly Activity Calendar
Books to Print
Site Index

K-3
Crafts
K-3 Themes
Little Explorers
Picture dictionary
PreK/K Activities
Rebus Rhymes
Stories
Writing
Cloze Activities
Essay Topics
Newspaper
Writing Activities
Parts of Speech

Fiction
The Test of Time

Biology
Animal Printouts
Biology Label Printouts
Biomes
Birds
Butterflies
Dinosaurs
Food Chain
Human Anatomy
Mammals
Plants
Rainforests
Sharks
Whales
Physical Sciences: K-12
Astronomy
The Earth
Geology
Hurricanes
Landforms
Oceans
Tsunami
Volcano
Languages
Dutch
French
German
Italian
Japanese (Romaji)
Portuguese
Spanish
Swedish
Geography/History
Explorers
Flags
Geography
Inventors
US History

Other Topics
Art and Artists
Calendars
College Finder
Crafts
Graphic Organizers
Label Me! Printouts
Math
Music
Word Wheels

Click to read our Privacy Policy

E-mail


Enchanted Learning Search

Search the Enchanted Learning website for:



Advertisement.

Advertisement.


Copyright ©1996-2018 EnchantedLearning.com ------ How to cite a web page