Transcript History of the Earth

History of the Earth
CA Standard 8e
Chapter 17
17-1 The Age
of the Earth
• Earth’s age is estimated at 4.6
billion years.
• James Hutton in 1788- proposed
that features of the earth were
influenced by volcanoes, erosion,
etc.. These things all act very
slowly
• In 1830, Charles Lyell agreed
that the earth had been shaped
over a long period of time…but
also stressed the importance of
explaining theory in terms of
scientific method.
Geologic Time Scale
• Relative Dating- the age of
some rocks “relative” to others
based on their position.
NEWER: RECENTLY DEPOSITED
OLDER: DEPOSITED EARLIER
• Absolute Dating: using
scientific techniques to find the
approximate actual age of
artifacts.
• Radioactive Dating: using the
known rate of decay to calculate
the age of artifacts. (14C)
Element
Half Life
Rubidium-87
50 billion years
Thorium-232
13.9 billion years
Uranium-238
4.5 billion years
Potassium-40
1.3 billion years
Uranium-235
713 million years
Carbon-14
5770 years
17-1 The Fossil Record
• Fossils- preserved remains of
ancient organisms
• Formation of fossils- when
animals are buried in some
medium that prevents decay
–mud, sand, silt, tar pits
–Sedimentary Rock
Problems with the
Fossil Record:
• Specific conditions are required
for fossils to form
–mountains vs. rivers and streams
–many organisms never fossilize
• Not all fossils have been found
• The quality of fossils varies
greatly
• As a result, the fossil record is
not as complete as
paleontologists would like
Cabrian: 500 million
Triassic:
250 million
Jurassic: 200 million
Trilobite
The Fossil Record
• Collectively, the millions of
fossils that have been collected
make up The Fossil Record
• Many pieces are missing
• Scientists have been able to
construct detailed paths of change
through time for many species
• Evidence indicates that Earth’s
climate has changed significantly
over time
• Evidence also shows that species
of plants and animals changed to
fit those environments, or
perished.