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| OVERVIEW |
Approximate
Dates: 2.5 bya–542 mya |
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| Defining Characteristics:
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Secondary Characteristics:
- • 4 major mountain-building
episodes
- • oldest known glaciation
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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.
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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
Department of Paleobiology Home |
National Museum of Natural History Home
Smithsonian Institution Home
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