1. Table of Contents Darwin’s Theory Evidence of Evolution
The Fossil Record

2. Darwin’s Voyage - Darwin’s Theory
Charles Darwin sailed on the Beagle, from England to the Galápagos Islands.

3. Overproduction and Variation
- Darwin’s Theory
Overproduction and Variation
Natural selection is the process by which individuals who are better adapted to their environment are more likely to survive and reproduce than other members of the same species.

4. Competition and Selection
- Darwin’s Theory
Competition and Selection
Variations among turtles make some of them better able to survive. Turtles that survive to become adults will be able to reproduce.

5. Relating Cause and Effect
- Darwin’s Theory
Relating Cause and Effect
In a graphic organizer, identify factors that cause natural selection.
Causes
Overproduction: More offspring are produced than can survive.
Variations: Members of the same species differ.
Competition: Offspring compete for survival.
Effect
Natural Selection
Selection: Some variations make individuals better fit for survival.
Environmental Change: Changes can affect an individual’s survival.
Genes: Genes that help determine survival are passed from parent to offspring.

6. Links on Charles Darwin
- Darwin’s Theory
Links on Charles Darwin
Click the SciLinks button for links on Charles Darwin.

7. End of Section: Darwin’s Theory

8. Homologous Structures
- Evidence of Evolution
Homologous Structures
The structure of the bones in a dolphin’s flipper, a bird’s wing, and a dog’s leg is similar. Homologous bones are shown in the same color.

9. A Branching Tree - Evidence of Evolution
This branching tree shows how scientists now think that raccoons, lesser pandas, giant pandas, and bears are related.

10. Kaibab and Abert’s Squirrels
- Evidence of Evolution
Kaibab and Abert’s Squirrels
These two kinds of squirrels have been isolated from one another for a long time. Eventually this isolation may result in two different species.

11. Identifying Supporting Evidence
- Evidence of Evolution
Identifying Supporting Evidence
Evidence consists of facts that can be confirmed by testing or observation. As you read, identify the evidence that supports the theory of evolution. Write the evidence in a graphic organizer like the one below.
Evidence
Fossils show that organisms that lived in the past were very different from organisms alive today.
Theory
Patterns of early development show that some different organisms look similar during their early stages.
Evolution
Similar body structures in different species show that the organisms shared a common ancestor.

12. Click the SciLinks button for links on evolution.
- Evidence of Evolution
Links on Evolution
Click the SciLinks button for links on evolution.

13. End of Section: Evidence of Evolution

14. How Do Fossils Form? - The Fossil Record
Most fossils form when organisms that die become buried in sediments.

15. Fossil Formation Activity
- The Fossil Record
Fossil Formation Activity
Click the Active Art button to open a browser window and access Active Art about fossil formation.

16. Radioactive Decay - The Fossil Record
The half life of potassium-40, a radioactive element, is 1.3 billion years. This means that half of the potassium-40 in a sample will break down into argon-40 every 1.3 billion years. The graph shows the breakdown of a 1-gram sample of potassium-40 into argon-40 over billions of years.

17. Radioactive Decay - The Fossil Record Reading Graphs:
What does the red line represent? What does the blue line represent?
The red line represents the amount of potassium-40. The blue line represents the amount of argon-40.

18. Radioactive Decay - The Fossil Record Reading Graphs:
At 2.6 billion years ago, how much of the sample consisted of potassium-40? How much of the sample consisted of argon-40?
Potassium-40–100%; argon-40–0%

19. Radioactive Decay - The Fossil Record Reading Graphs:
At what point in time do the two graph lines cross?
About 1.3 billion years

20. Radioactive Decay - The Fossil Record Interpreting Data:
At the point where the graph lines cross, how much of the sample consisted of potassium-40? How much consisted of argon-40? Explain why this is the case.
50% of each; the half-life of potassium-40 is 1.3 billion years, which means that half will break down into argon-40 every 1.3 billion years.

21. Earth’s History as a Clock
- The Fossil Record
Earth’s History as a Clock
Fossils found in rock layers tell the history of life on Earth. The history of life can be compared to 12 hours on a clock.

22. Precambrian Time and the Paleozoic Era
- The Fossil Record
Precambrian Time and the Paleozoic Era

23. Mesozoic and Cenozoic Eras
- The Fossil Record
Mesozoic and Cenozoic Eras

24. Building Vocabulary - The Fossil Record
After you read the section, write a definition of each Key Term in your own words.
Key Terms:
Examples:
punctuated equilibria
Key Terms:
Key Terms:
Examples:
radioactive element
half-life
fossil record
extinct
gradualism
Examples:
petrified fossil
Fossils that form by minerals replacing remains are called petrified fossils.
The rocks that fossils are found near contain radioactive elements, which are unstable elements that decay, or break down, into different elements.
The theory of punctuated equilibria accounts for the gaps in the fossil record.
mold
A hollow space in the sediment in the shape of an organism or part of an organism is called a mold.
The half-life of a radioactive element is the time it takes for half of the atoms in a sample to decay.
cast
A cast is a copy of the shape of the organism that made a mold.
The millions of fossils that scientists have collected are called the fossil record.
relative dating
Scientists use relative dating to determine which of two fossils is older.
A species is extinct if no members of that species are still alive.
radioactive dating
A technique called radioactive dating allows scientists to determine the actual age of fossils.
Gradualism proposes that evolution occurs slowly but steadily.

25. Click the Video button to watch a movie about fossils.
- The Fossil Record
Fossils
Click the Video button to watch a movie about fossils.

26. End of Section: The Fossil Record

27. Graphic Organizer Fossil Formation An organism dies in water.
The organism is buried under sediment.
Over millions of years, the sediments harden and become rock, and the hard parts of the organism are replaced by minerals.
The fossil becomes exposed on the surface of a rock.

28. End of Section: Graphic Organizer