Chapter 8- Earth’s History
CUE WORDS or QUESTIONS
What is the study of the earth?
X
What is uniformitarianism?
What are the three types of
rock and how did they form?
NOTES WRITTEN
Geology- study of the earth
Uniformitarianism- the same geologic processes that operate today
operated in the past (and these processes take a long, long time!)
Three types of rock:
1. Igneous- forms from molten material (lava or magma)
2. Sedimentary- forms from sediment (broken down rock)
 May contain fossils
3. Metamorphic- forms from existing rocks with heat and pressure
Rock cycle- process by which rocks change from one type of rock into
another
What is relative dating?
Law of superposition-
X
How are index fossils chosen?
Relative age of rocks- age compared to age of other rocks
Law of superposition- newest rock layers on top, oldest on bottom
Unconformity- a gap in the fossil record; new rock layers meet older rock
layers (due to erosion)
Index fossil- fossils that are used to determine relative age of rocks
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What is the difference between
absolute dating and
relative dating?
Fossils are widely distributed (found in many areas)
Existed briefly (only occurs in one layer)
Absolute age of rocks- age of rocks based on half-life
Element- all atoms in one type of matter (like carbon or nitrogen)
Atom- tiny particles that make up everything
Radioactive decay- process of elements breaking down
Half-life- time it takes for half of the radioactive atoms in an element to decay
How old is the Earth?
Scientists used radioactive dating to determine earth is 4.6 billion years old
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SUMMARY
X
Partly based on moon rocks and meteorites
CUE WORDS or QUESTIONS
NOTES WRITTEN
Geologic time scale- record of life forms and geologic events throughout
Earth’s history
X
What is an era?
Era- unit of time from Precambrian to present
 divided into periods, periods divided into epochs
 determined by major changes on Earth (catastrophic events that
 caused mass extinctions
What is Precambrian time?
Precambrian Time- 4.6 bya- 544 mya
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What happened in the
Paleozoic era?
X What happened in the
Mesozoic era?
What happened in the
Cenozioc era?
SUMMARY
X
Longest period of time
3.5 bya-bacteria (first living thing)
600 mya- first animal (jelly fish)
Paleozoic Era- 544 mya- 245 mya
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“ancient life”
Invertebrates and vertebrates evolve
Life moves to land and reptiles evolve
Ends with a mass extinction (Pangaea forming changed the climate)
Mesozoic Era- 245- 66 mya
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“age of dinosaurs” (dinosaurs dominate the land)
“middle life”
Ends with mass extinction (asteroid impact)
Cenozoic Era- 66 mya- present time
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Most recent and shortest era
“age of mammals” (mammals dominate the land)
Humans evolve (about 100,000 ya)