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Views of Earth’s Past
the BIG idea
Rocks, fossils, and other types of natural evidence tell Earth’s story.
9.1
Earth’s past is revealed in rocks and fossils.
9.2
Rocks provide a timeline for Earth.
9.3
The geologic time scale shows Earth’s past.
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2. 9.1 Earth’s past is revealed in rocks and fossils.
Fossils are traces or remnants of past life. Many fossils are found in rock. Rocks, fossils, and other natural evidence provide information about how Earth and life on Earth have changed over time.
fossil
original remains
ice core
A cast fossil is formed when minerals take the shape of a decayed organism.
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Explore how fossils form.
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3. 9.1 Trace Fossils Earth’s past is revealed in rocks and fossils.
original remains
ice core
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4. Rocks provide a timeline for Earth.
9.2
Rocks provide a timeline for Earth.
Sedimentary rock layers show the order in which rocks formed. The order of the layers is used to determine the relative ages of fossils found in the rock.
relative age
index fossil
absolute age
half-life
Radioactive dating can be used to determine the absolute age of igneous rock.
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Scientists combine information about the relative and absolute ages of rocks and fossils to construct a timeline of Earth.
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5. Rocks provide a timeline for Earth.
9.2
Rocks provide a timeline for Earth.
Scientists combine information about the relative and absolute ages of rocks and fossils to construct a timeline of Earth.
relative age
index fossil
absolute age
half-life
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Watch molten rock cut through layers of sedimentary rock.
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6. The geologic time scale shows Earth’s past.
9.3
The geologic time scale shows Earth’s past.
The geologic time scale divides Earth’s history into eons, eras, periods, and epochs.
The divisions are based on major changes or events that occurred in Earth’s history.
uniformitarianism
geologic time scale
EON
EPOCH
ERA
PERIOD
today
*bya = billion years ago †mya = million years ago
Phanerozoic eon
Cenozoic era
Mesozoic era
Paleozoic era
Proterozoic eon
Archean eon
Hadean eon
Precambrian time
500 mya†
4.6 bya*
3 bya
2 bya
1 bya
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7. Earth’s past is revealed in rocks and fossils.
9.1
Earth’s past is revealed in rocks and fossils.
I. Earth’s past is revealed in rocks and fossils.
fossil
A. Rocks, fossils, and original remains give clues about the past.
original remains
ice core
1. Original Remains
2. Fossil Formation
3. Fossils in Rocks
B. Fossils and other natural evidence show changes in life and the environment.
1. Tree Rings
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2. Ice Cores
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8. Rocks provide a timeline for Earth.
9.2
Rocks provide a timeline for Earth.
II. Rocks provide a timeline for Earth.
relative age
A. Layers of sedimentary rocks show relative age.
index fossil
absolute age
1. Igneous Rock and Sedimentary Layers
half-life
2. Index Fossils
B. Radioactive dating can show absolute age.
1. Half-Life
2. Using Absolute and Relative Age
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9. The geologic time scale shows Earth’s past.
9.3
The geologic time scale shows Earth’s past.
III. The geologic time scale shows Earth’s past.
uniformitarianism
A. Earth is constantly changing.
geologic time scale
B. The geologic time scale divides Earth’s history.
1. Divisions of Geologic Time
2. Phanerozoic Eon
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