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Name: _____________________________________Date: ________________
Earth Science
Mr. Herman
Exeter SHS
Chapter 13.1 Precambrian Time
Describe the history of Precambrian time.
Compare Earth’s original atmosphere and geosphere to its atmosphere and
geosphere today
Explain how scientists know about the conditions on Earth during the
Precambrian time.
Anticipatory Questions
1. Where do we find the closest exposed Precambrian rock?
2. What was Earth’s original atmosphere made up of?
3. Why was there life during the Precambrian?
Precambrian History
 The Precambrian encompasses immense geological time, from Earth’s distant
beginnings 4.56 billion years ago until the start of the Cambrian period, over 4
billion years later.
Precambrian Rocks
 Shields are large, relatively flat expanses of ancient metamorphic rock within the
stable continental interior.
 Much of what we know about Precambrian rocks comes from ores mined from
Precambrian Atmosphere
 Earth’s original atmosphere could not support life as we know it now.
The atmosphere was composed of gases similar to those released by volcanoes;
water vapor, CO2, N2 and several other trace gases. No O2
 Later organism evolved that used photosynthesis and released O2
 Oxygen began to accumulate in the atmosphere about 2.5 million years ago
Precambrian Fossils
 The most common Precambrian fossils are stromatolites.
 Stromatolites are distinctively layered mounds or columns of calcium carbonate.
They are not the remains of actual organisms but are the material deposited by
 Many of these ancient fossils are preserved in chert—a hard dense chemical
sedimentary rock.
Precambrian Pennsylvania
During the Precambrian, Pennsylvania was mainly a low, featureless plain sloping
gently southeastward toward the sea.
Most of Pennsylvania's exposed Precambrian rocks are metamorphic and igneous,
and thus lack fossils.