Download P337\Section 4

P337\Section 4
Geologic Time Scale
• 1a How long ago did the Earth form?
• 4.6 billion years ago
• Summarize the process by which scientists
determined the age of Earth.
• Scientists studies rock layers and fossils
worldwide and placed Earth’s rock layers in
order by relative age. Later, radioactive dating
helped them determine the absolute ages of
the divisions.
• What are the basic units into which the
geologic time scale is divided?
• The geologic time scale is divided into eras
and periods.
• Study figure 14. (p336) Which major division
of time was the longest?
• Precambrian
• When did it begin?
• 4.6 BYA
• When did it end?
• 544 MYA
• Place the following in the correct order from
earliest to latest: Tertiary, Jurassic,
Quaternary, Triassic, and Cretaceous.
• Triassic, Jurassic, Cretaceous, Tertiary, and
Quaternary
Section 5
Early Earth
p. 341e
• 1a How long ago did the Earth form?
• The Earth formed about 4.6 billion years ago
• Summarize the process by which scientists
determined the age of the Earth.
• Scientists used radioactive dating of rocks
from Earth and moon to determine the age of
the Earth.
• What physical features formed during Earth’s
first several hundred million years?
• Oceans, the atmosphere, and continents were
formed.
• How did volcanic eruptions and comets
change early Earth?
• Volcanic eruptions released carbon dioxide
into the atmosphere, and comets released
water vapor.
•
What caused water erosion to begin on Earth’s
surface?
• Rain
• What do scientists think were the first
organisms to evolve on Earth?
• Organisms similar to our present day bacteria
were probably the first life forms.
• How would Earth’s atmosphere be different if
organisms capable of photosynthesis had not
evolved?
• The Earth’s atmosphere would have little or
no oxygen. A by-product of photosynthesis is
oxygen.