LESSON 2: ANCIENT EARTH
Essential Questions
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How did gravity affect Earth’s formation?
How did the oceans and atmosphere form?
What conditions made early Earth able to support
life?
How did environmental changes affect the evolution
of life?
Vocabulary
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Hadean eon
Archean eon
Protocontinent
Proterozoic eon
Thermal energy
Earth’s Earliest History
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Gravity and the Solar System
 Before Earth or even the solar system existed, a cloud
of gas, ice, and dust, called a nebula, floated in
space
Earth’s Earliest History
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First: Gravity pulled the particules together into a
flattened disk shape and began to rotate.
Second: the material in the center became dense
and the Sun formed
Third: the remaining pieces of material in the disk
attracted each other and planets were formed
Spherical Earth
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As more particles come together Earth became
larger.
 Thermal
energy is produced by collisions, which
warmed the planet.
 Asteroids continued to crash into the Earth surface,
making it even hotter.
Hadean Eon, Archean Eon, Proterozoic Eon
Hadean Eon
The first 640 million years of Earth history
Hadean Eon
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The first 640 million years of Earth history
Formation of Earth’s Core
A hot Earth cools
Seas of Molten Rock
Changes in the Seas
The Ancient Athmosphere
Archean Eon
From about 4 to 2.5 billion years ago
Archean Eon
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Earth continues to cool and first solid surface appeared, but still
twice as much internal thermal energy was produced at that time,
comparing to nowadays.
Volcanic Activity
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The Earliest Continents
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As magna rised to the surface through cracks in the ocean floor it has
formed Earth first oceanic crust.
Protocontinents: small and early continents which have collied between
each other forming bigger landmasses
Earth’s Oceans Form
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Fossil bacteria and stromatolites are the earliest evidence of life present
in rocks. They are uncommon and difficult to see due to their microscopic
size.
The Archean oceans were extreme environments, most organisms alive
today would not have survived then.
Proterozoic Eon
From 2.5 to 0.542 billion years ago
Proterozoic Eon
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Changes in the Atmosphere: Earth was cooling down
and larger landmasses were formed.
 Increase
in Oxygen
 Snowball Earth
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Supercontinents and Shallow Seas
Proterozoic Life
 Unicellular
organisms in water.
 First multicellular organisms in the ocean, but had no
hard parts, so fossils aren’t abundant.
Homework
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Textbook: Page 94 #2, 3, 4
Workbook: Page