Smithsonian National Museum of Natural History Geologic Time The Story of a Changing Earth
Presented by the Department of Paleobiology.
The Proterozoic
Contents
Eon Overview
Earth's Crust as a Platform for Prokaryotic Life
Eukaryotes and the First Multicellular Life Forms
Changes in the Earth's Atmosphere
Proterozoic Mountains and Glaciers
Evidence
Rangea from the Ediacaran Fauna, Namibia.
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sample
First eukaryotes
Ediacaran Fauna 1
Ediacaran Fauna 2
Ediacaran Fauna 3
Ediacaran Fauna 4
Banded Iron Formations
Stromatolites
references and links
Foundational Concepts
Dating Methods
Earth Processes
Life Processes
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OVERVIEW
Approximate Dates: 2.5 bya–542 mya
Defining Characteristics:
  • • first multicellular animals at end of interval
  • • Map of the Proterozoic World
Secondary Characteristics:
  • • 4 major mountain-building episodes
  • • oldest known glaciation

The term Proterozoic comes from the Greek words proteros (meaning “first”) and zoon (meaning “life”). Although early fossils are now thought to occur in older, Archean rocks, for many years the oldest evidence of life was known from Proterozoic strata. The Proterozoic represents the last stage of what was once called the Precambrian—the 3.7-billion-year-long period before the Paleozoic Era. Rocks of this age are known from Australia, Canada, and China.

During the Proterozoic, larger continental landmasses continued to form by the accretion of smaller ones, often leading to extensive mountain-building. As the continents began to erode, sediments were washed into the oceans, producing shallow-water marine environments where life could flourish and diversify. Many of these life forms developed the ability to photosynthesize. As a byproduct of photosynthesis, they created oxygen, and over billions of years this oxygen transformed the Earth’s atmosphere. Because oxygen was toxic to some early life forms, many went extinct. Others thrived and evolved into the first multicellular organisms, which are preserved as the Ediacaran fauna. Both the beginning and end of the Proterozoic were marked by widespread glaciation.



Eon Overview | Earth's Crust as a Platform for Prokaryotic Life | Eukaryotes and the First Multicellular Life Forms | Changes in the Atmosphere | Proterozoic Mountains and Glaciers



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