Section 22'1 Early Earth

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Section 22.1 Early Earth
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Key Concepts
Study Guide
Several lines of evidence indicate that Earth
is about 4.56 billion years old.

• Scientists use Earth rocks, zircon crystals, moon
  rocks, and meteorites to determine Earths age.

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Section 22.1 Early Earth
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Study Guide
Key Concepts

• Likely heat sources of early Earth were
  gravitational contraction, radioactivity, and
  asteroid and meteorite bombardment.
• Cooling of Earth led to the formation of liquid
  water.

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Section 22.2 Formation of the Crust and Continents
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Study Guide
Key Concepts
The molten rock of Earths early surface formed
into crust and then continents.

• Earth differentiated into specific density zones
  early in its formation.
• Plate tectonics caused microcontinents to collide
  and fuse throughout the Proterozoic.

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Section 22.2 Formation of the Crust and Continents
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Study Guide
Key Concepts

• The ancient continent of Laurentia formed as a
  result of many mountain-building episodes.
• Earths first supercontinent formed at the end of
  the Proterozoic.

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Section 22.3 Formation of the Atmosphere and
Oceans
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Study Guide
Key Concepts
The formation of Earths oceans and atmosphere
provided a hospitable environment for life to
begin.

• Earths atmosphere and oceans began forming early
  in Earths history.
• Oxygen gas began to accumulate in the Proterozoic
  by photosynthesizing cyanobacteria.

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Section 22.3 Formation of the Atmosphere and
Oceans
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Study Guide
Key Concepts

• Evidence for atmospheric oxygen can be found in
  rocks.
• The water that filled Earths oceans most likely
  came from two major sources.

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Section 22.4 Early Life on Earth
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Study Guide
Key Concepts
Life began on Earth fewer than a billion years
after Earth formed.

• Scientists think that life on Earth began between
  3.9 and 3.5 bya.
• Stanley Miller and Harold Urey were the first to
  show experimentally that organic molecules could
  have formed on early Earth.

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Section 22.4 Early Life on Earth
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Study Guide
Key Concepts

• Scientists have developed several hypotheses to
  explain how and where life formed.
• Eukaryotes appeared after prokaryotes.
• Earths first multicellular organisms evolved at
  the end of the Precambrian.

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22.1 Section Questions
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The Precambrian Earth
The Precambrian lasted for nearly 4 billion years.
a. true b. false
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22.1 Section Questions
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The Precambrian Earth
Which is used as evidence of Earths age?
a. Moon rock samples b. metamorphic rocks
c. comet fragments d. iron-oxide molecules
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22.1 Section Questions
22
The Precambrian Earth
Earth was extremely hot after it first formed.
What was one of the sources of that extreme heat?
a. solar radiation b. radioactive decay
c. volcanic events d. metamorphism
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22.2 Section Questions
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The Precambrian Earth
What is the process by which a planet develops
layers as denser materials sink toward the center
and less dense materials rise toward the surface?
a. continent formation b. continental drift
c. consolidation d. differentiation
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22.2 Section Questions
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The Precambrian Earth
The microcontinents that formed early in Earths
history still exist as the cores of Earths
continents. What are those cores called?
a. cratons b. plutons c. granite d. basalt
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22.2 Section Questions
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The Precambrian Earth
Rodinia was Earths first supercontinent.
a. true b. false
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22.3 Section Questions
22
The Precambrian Earth
Earths atmosphere contained large amounts of
free oxygen 4.5 billion years ago.
a. true b. false
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22.3 Section Questions
22
The Precambrian Earth
What discovery is strong evidence for the
existence of cyanobacteria 3.5 billion years ago?
a. fossil stromatolites b. sedimentary red beds
c. banded-iron formations d. Archean iron
oxides
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22.3 Section Questions
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The Precambrian Earth
What is the probable source of water in Earths
atmosphere and oceans?
Answer The water probably came from asteroids,
comets, and other space objects, as well as from
volcanic outgassing.
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22.4 Section Questions
22
The Precambrian Earth
Experiments suggest that RNA molecules may have
been the first replicating molecules on Earth.
a. true b. false
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22.4 Section Questions
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The Precambrian Earth
What most likely played a major role in the mass
extinction of eukaryotes about 750 million years
ago?
a. an asteroid impact b. widespread glaciation
c. widespread volcanism d. predation by
prokaryotes
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22.4 Section Questions
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The Precambrian Earth
Why did life not flourish on Earth before about 4
billion years ago?
Answer Until about 4 billion years ago, Earth
was still subject to steady asteroid impacts.
Large impacts could have destroyed many early
life forms.
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Chapter Assessment Questions
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The Precambrian Earth
Using radiometric dating, which material is
likely to be the oldest?
a. iron oxide b. zircon c. granite d. basalt
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Chapter Assessment Questions
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The Precambrian Earth
What was Laurentia?
Possible answer Laurentia was the ancient
continent of North America and one of Earths
largest Proterozoic landmasses. It collided with
Amazonia in the Grenville Orogeny at the end of
the Proterozoic and became part of Rodinia,
Earths first supercontinent.
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Chapter Assessment Questions
22
The Precambrian Earth
What was essential for the formation of Earths
first continental crust?
a. formation of a supercontinent b. presence of
water in the mantle c. asteroid and meteorite
impacts d. oxygen in the early atmosphere
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Chapter Assessment Questions
22
The Precambrian Earth
How did scientists conclude that atmospheric
oxygen did not exist in large amounts until the
Proterozoic Eon?
Possible answer Iron oxides are not found in
rocks that were formed before the Proterozoic
Eon. If Earths atmosphere had contained oxygen,
it would have reacted with the iron in the rocks
to form iron oxides.
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Chapter Assessment Questions
22
The Precambrian Earth
Where is most of Earths iron located?
Answer Most of Earths iron is in or near its
core.
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Standardized Test Practice
22
The Precambrian Earth
Besides being necessary for animal life, why else
is the presence of oxygen in the atmosphere
important?
Possible answer Oxygen forms ozone in the
atmosphere, which provides protection from
ultraviolet radiation from the Sun.
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Standardized Test Practice
22
The Precambrian Earth
What was the main source of Earths atmospheric
oxygen?
a. volcanic outgassing b. photosynthesis
c. ocean formation d. Archean atmosphere
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Standardized Test Practice
22
The Precambrian Earth
Which of Earths layers is the least dense?
a. A b. B c. C d. D
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Standardized Test Practice
22
The Precambrian Earth
In which layer are you most likely to find
granite?
a. A b. B c. C d. D
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Standardized Test Practice
22
The Precambrian Earth
How long did it take for Earth to cool enough for
the first oceans to form?
a. about 200 years b. about 200,000 years
c. about 2 million years d. about 200 million
years