The History of Life
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.
17-1: The Fossil Record
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
After Precambrian Time, the basic divisions
of the geologic time scale are eras and periods.
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.
17-3: Evolution of Multicellular Life
Early in the Paleozoic
Era, the fossil record became rich with evidence of many types of marine
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 environmentson
land, in water, and even in the air.
17-4: Patterns of Evolution
Six important patterns
of macroevolution are mass extinctions, adaptive radiation, convergent
evolution, coevolution, punctuated equilibrium, and changes in developmental