Wednesday 12/16/15 Learning Goal: Explain how fossils form, how scientists determine a fossil’s...
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Transcript of Wednesday 12/16/15 Learning Goal: Explain how fossils form, how scientists determine a fossil’s...
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Wednesday 12/16/15Learning Goal: Explain how fossils form, how scientists determine a fossil’s age, and the Geologic Time Scale.
Warm-up:How do most fossils form?
Homework:Chapter 6 test on Wednesday!
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How do most fossils form?
A dead organism becomes buried in sediment
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Chapter 6 Section 3
The Fossil Record
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FossilsThe preserved remains or traces of
organisms that lived in the past
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How Do Fossils Form?
Hard parts of organisms form fossilsBones, Shells
Most fossils form when organisms that die become buried in sediments (particles of soil and rock)
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Types of FossilsPetrified Fossils
Remains of organisms that are actually changed to rock
Molds and CastsMold: a hollow space in sediment in the shape
of an organism (cake pan)Cast: a copy of the shape of the organism that
made the mold (cake)Preserved Remains
Can be preserved in other substances other than sedimentsICE
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Determining a Fossil’s AgeRelative Dating Radioactive Dating
a technique used to determine which two fossils are older
• Oldest layer at bottom• Younger layer at top
a technique used to determine the actual age of fossil on the basis of the amount of a radioactive element it contains
• Radioactive elements: unstable elements that decay, or break down, into different elements
• Half-life: the time it takes for half of the atoms in a radioactive element to decay
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Radioactive Decay
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What Do Fossils Reveal?
Fossil record: the millions of fossils that scientists have collected
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Extinct OrganismsExtinct: no members of that species are
still aliveMost of what scientists know about extinct
species is based on the fossil record
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The Geologic Time ScaleThe calendar of Earth’s historyThe largest span of time in the Geologic
Time Scale is Precambrian TimeThis is when living things appeared on Earth
Page 194-195
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Mass ExtinctionsExtinction of many types of organisms at
the same timeCretaceous Period, about 65 million years
ago (plants, animals, dinosaurs)
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Gradualism
A theory that proposes evolution occurs steadily in tiny changes over long periods of time
This is how Darwin thought evolution occurred
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Punctuated Equilibria
the theory that species evolve during short periods of rapid change