Chapter 17
The History of Life

In this chapter, students will read about the major periods and events in the history of life on Earth. Students will also read about the use of fossil stratigraphy and radioactive dating to establish the chronology of the fossil record and major patterns of macroevolutionThe links below lead to additional resources to help you with this chapter. These include Hot Links to Web sites related to the topics in this chapter, the Take It to the Net activities referred to in your textbook, a Self-Test you can use to test your knowledge of this chapter, and Teaching Links that instructors may find useful for their students.

What are Web Codes?

Web Codes for Chapter 17:: Active Art: Fossil Formation SciLinks: Fossil Record SciLinks: Eukaryotic Cells SciLinks: Extinction Self-Test

Section 17-1: The Fossil Record
The fossil record provides evidence about the history of life on Earth. It also shows how different groups of organisms have changed over time.
Relative dating allows paleontologists to estimate a fossil's age compared with that of other fossils.
In radioactive dating, scientists calculate the age of a sample based on the amount of remaining radioactive isotopes it contains.
After Precambrian Time, the basic divisions of the geologic time scale are eras and periods.

Section 17-2: Earth's Early History
Earth's early atmosphere probably contained hydrogen cyanide, carbon dioxide, carbon monoxide, nitrogen, hydrogen sulfide, and water.
Miller and Urey's experiments suggested how mixtures of the organic compounds necessary for life could have arisen from simpler compounds present on a primitive Earth.
The rise of oxygen in the atmosphere drove some life forms to extinction, while other life forms evolved new, more efficient metabolic pathways that used oxygen for respiration.
The endosymbiotic theory proposes that eukaryotic cells arose from living communities formed by prokaryotic organisms.

Section 17-3: Evolution of Multicellular Life
Early in the Paleozoic Era, the fossil record became rich with evidence of many types of marine life.
During the Devonian, animals began to invade the land.
The mass extinction at the end of the Paleozoic affected both plants and animals on land and in the seas. As much as 95 percent of the complex life in the oceans disappeared.
Events during the Mesozoic include the increasing dominance of dinosaurs. The Mesozoic is marked by the appearance of flowering plants.
During the Cenozoic, mammals evolved adaptations that allowed them to live in various environments—on land, in water, and even in the air.

Section 17-4: Patterns of Evolution
Six important patterns of macroevolution are mass extinctions, adaptive radiation, convergent evolution, coevolution, punctuated equilibrium, and changes in developmental genes.