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The Fossil Record Chapter 6 Section 3.

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Presentation on theme: "The Fossil Record Chapter 6 Section 3."— Presentation transcript:

1 The Fossil Record Chapter 6 Section 3

2 Fossils The preserved remains or traces of organisms that lived in the past

3 How Do Fossils Form? Hard parts of organisms form fossils
Bones, Shells Most fossils form when organisms that die become buried in sediments (particles of soil and rock)


5 Types of Fossils Petrified Fossils Molds and Casts Preserved Remains
Remains of organisms that are actually changed to rock Molds and Casts Mold: 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 sediments ICE

6 Determining a Fossil’s Age
Relative 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

7 Radioactive Decay

8 What Do Fossils Reveal? Fossil record: the millions of fossils that scientists have collected

9 Extinct Organisms Extinct: no members of that species are still alive
Most of what scientists know about extinct species is based on the fossil record

10 The Geologic Time Scale
The calendar of Earth’s history The largest span of time in the Geologic Time Scale is Precambrian Time This is when living things appeared on Earth Page

11 Mass Extinctions Extinction of many types of organisms at the same time Cretaceous Period, about 65 million years ago (plants, animals, dinosaurs)

12 Gradualism A theory that proposes evolution occurs steadily in tiny changes over long periods of time This is how Darwin thought evolution occurred

13 Punctuated Equilibria
the theory that species evolve during short periods of rapid change

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