Eighth Edition
by Harold L. Levin

Chapter 9 - page 1

The Proterozoic: Dawn of a More Modern World

Introduction

Proterozoic Eon = 2.5 billion years ago to 542 million years ago.
Comprises 42% of Earth history.

The beginning of the Proterozoic at 2.5 by marks the beginning of:

• More modern style of plate tectonics.
• More modern style of sedimentation.
• More modern global climate with glaciations.
• Establishment of the beginnings of an oxygen-rich atmosphere.
• Emergence of an aerobic biosphere (eukaryotes).

Proterozoic Eon can be divided into three eras:

1. Paleoproterozoic Era (2.5 - 1.6 by ago)
2. Mesoproterozoic Era (1.6 to 1.0 by ago)
3. Neoproterozoic Era (1.0 by ago to the beginning of the Paleozoic, 542 my ago)

Proterozoic rocks are easier to study than Archean rocks because they are less altered.
They are more difficult to study than Phanerozoic rocks because they lack the abundant fossils.

Plate Tectonics

Precambrian provinces of North America were welded (or sutured) together to form a large continent called Laurentia during the early Proterozoic.
Suturing occurred along mountain belts or orogens.
Provinces were assembled by about 1.7 by.
Laurentia continued to grow by accretion throughout the Proterozoic.

Precambrian provinces in North America, with dates.
Oldest (Archean) rocks are shown in orange.
Younger (Proterozoic) rocks are shown in green.

Late in the Proterozoic, the continents became assembled into a supercontinent called Rodinia.

Sedimentation

Sedimentation on and around the craton consisted of shallow water clastic and carbonate sediments deposited on broad continental shelves and in epicontinental seas.

Climate

Proterozoic glaciations occurred during the:

1. Paleoproterozoic, about 2.4-2.3 by ago (Huronian glaciation).
2. Neoproterozoic, 850-600 my ago (Varangian glaciation).

Overview of events of the Proterozoic.