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3. Chapter 9 A View of Earth’s Past Table of Contents Section 1 Geologic Time Section 2 Precambrian Time and the Paleozoic Era Section 3 The Mesozoic and Cenozoic Eras

4. Chapter 9 Section 1 Geologic Time Objectives • Summarizehow scientists worked together to develop the geologic column. • Listthe major divisions of geologic time.

5. Chapter 9 Section 1 Geologic Time The Geologic Column geologic column an ordered arrangement of rock layers that is based on the relative ages of the rocks and in which the oldest rocks are at the bottom. • Evidence of changing conditions on Earth’s surface is recorded in the rock layers of Earth’s crust. • The geologic time scale outlines the development of Earth and of life on Earth. • No single area on Earth contained a record of all geologic time, so scientists combined observations to create a standard geologic column.

6. Chapter 9 Section 1 Geologic Time The Geologic Column, continued • Rock layers in a geologic column are distinguished by the types of rock the layers are made of and by the kinds of fossils the layers contain. • Fossils in the upper layers resemble modern plants and animals. • Many of the fossils discovered in old layers are from species that have been extinct for millions of years.

7. Chapter 9 Section 1 Geologic Time The Geologic Column, continued Reading Check Where would you find fossils of extinct animals on a geologic column?

8. Chapter 9 Section 1 Geologic Time The Geologic Column, continued Reading Check Where would you find fossils of extinct animals on a geologic column? You would find fossils of extinct animals in older layers of a geologic column.

9. Chapter 9 Section 1 Geologic Time The Geologic Column, continued Using a Geologic Column • Scientists use geologic columns to estimate the age of rock layers that cannot be dated radiometrically. • To determine the layer’s age, scientists compare a given rock layer with a similar layer in a geologic column that contains the same fossils or that has the same relative position. • If the two layers match, they likely formed at about the same time.

10. Chapter 9 Section 1 Geologic Time Divisions of Geologic Time • The geologic history of Earth is marked by major changes in Earth’s surface, climate, and types of organisms. • Geologists use these indicators to divide the geologic time scale into smaller units. • Rocks grouped within each unit contain similar fossils and each unit is generally characterized by fossils of a dominant life-form.

11. Chapter 9 Section 1 Geologic Time Divisions of Geologic Time, continued

12. Chapter 9 Section 1 Geologic Time Divisions of Geologic Time, continued Eons and Eras • The largest unit of geologic unit of time is an eon. Geologic time is divided into four eons: the Hadean eon, the Archean eon, the Proterozoic eon, and the Phanerozoic eon. • The first three eons are part of a time interval commonly known as Precambrian Time. This 4 billion year interval contains most of Earth’s history.

13. Chapter 9 Section 1 Geologic Time Divisions of Geologic Time, continued Eons and Eras eraa unit of geologic time that includes two or more periods • After Precambrian time the Phanerozoic eon began. This eon is divided into smaller units of geologic time called eras. • The first era of the Phanerozoic eon was the Paleozoic Era, which lasted 292 million years.

14. Chapter 9 Section 1 Geologic Time Divisions of Geologic Time, continued Eons and Eras • Paleozoic rocks contain fossils of a wide variety of marine and terrestrial life forms. • After the Paleozoic Era the Mesozoic Era began and lasted about 183 million years. • Mesozoic fossils include early forms of birds and reptiles. • The present era is the Cenozoic Era, which began 65 million years ago. Fossils of mammals are common in Cenozoic rocks.

15. Chapter 9 Section 1 Geologic Time Divisions of Geologic Time, continued Eons and Eras perioda unit of geologic time that is longer than an epoch but shorter than an era epocha subdivision of geologic time that is longer than an age but shorter than a period. • Eras are divided into shorter time units called periods. Each period is characterized by specific fossils and is usually named for the location in which the fossils were first discovered.

16. Chapter 9 Section 1 Geologic Time Divisions of Geologic Time, continued Eons and Eras • Where the rock record is most complete and least deformed, a detailed fossil record may allow scientists to divide period into shorter time units called epochs. • Epochs may be divided into smaller units of time called ages. • Ages are defined by the occurrence of distinct fossils in the fossil record.

17. Chapter 9 Section 1 Geologic Time Earth-History Clock

18. Section 2 Precambrian Time and the Paleozoic Era Chapter 9 Objectives • Summarizehow evolution is related to geologic change. • Identifytwo characteristics of Precambrian rock. • Identifyone major geologic and two major biological developments during the Paleozoic Era.

19. Section 2 Precambrian Time and the Paleozoic Era Chapter 9 Evolution evolutionan inheritable change in the characteristics within a population from one generation to the next; the development of new types of organisms from preexisting types of organisms over time • By examining rock layers and fossils, scientists have discovered evidence that species of livings things have changed over time. • Scientists call this process evolution.

20. Section 2 Precambrian Time and the Paleozoic Era Chapter 9 Evolution, continued Evolution and Geologic Change • Scientists think that evolution occurs by means of natural selection. Evidence for evolution included the similarity in skeletal structures of animals. • Major geologic and climatic changes can affect the ability of some organisms to survive. • By using geologic evidence, scientists try to determine how environmental changes affected organisms in the past.

21. Section 2 Precambrian Time and the Paleozoic Era Chapter 9 Evolution, continued

22. Section 2 Precambrian Time and the Paleozoic Era Chapter 9 Evolution, continued

23. Section 2 Precambrian Time and the Paleozoic Era Chapter 9 Precambrian Time Precambrian time the interval of time in the geologic time scale from Earth’s formation to the beginning of the Paleozoic era, from 4.6 billion to 542 million years ago. • The time interval that began with the formation of Earth and ended about 542 million years ago is known as Precambrian time, which makes up 88% of Earth’s history.

24. Section 2 Precambrian Time and the Paleozoic Era Chapter 9 Precambrian Time, continued

25. Section 2 Precambrian Time and the Paleozoic Era Chapter 9 Precambrian Time, continued • The Precambrian rock record is difficult to interpret, therefore we do not know much about what happened during that time. • Most Precambrian rocks have been so severely deformed and altered by tectonic activity that the original order of rock layers is rarely identifiable.

26. Section 2 Precambrian Time and the Paleozoic Era Chapter 9 Precambrian Time, continued Precambrian Rocks • Large areas of exposed Precambrian rocks, called shields, exist on every continent. • Nearly half of the valuable mineral deposits in the world occur in the rocks of Precambrian shields. • These valuable minerals include nickel, iron, gold, and copper.

27. Section 2 Precambrian Time and the Paleozoic Era Chapter 9 Precambrian Time, continued Precambrian Life • Fossils are rare in Precambrian rocks mostly because Precambrian life-forms lacked bones, or other hard parts that commonly form fossils. • One of the few Precambrian fossils that have been discovered are stromatolites. • The presence of stromatolite fossils in Precambrian rocks indicates that shallow seas covered much of Earth during that time.

28. Section 2 Precambrian Time and the Paleozoic Era Chapter 9 The Paleozoic Era Paleozoic Era the geologic era that followed Precambrian time and that lasted from 542 million to 251 million years ago. • Paleozoic rocks hold an abundant fossil record. The number of plant and animal species on Earth increased dramatically at the beginning of the Paleozoic Era. • Because of this rich fossil record, the Paleozoic Era has been divided into seven periods.

29. Section 2 Precambrian Time and the Paleozoic Era Chapter 9 The Paleozoic Era, continued The Cambrian Period • The Cambrian Period is the first period of the Paleozoic Era. • Marine invertebrates thrived in the warm waters that existed during this time. • The most common of the Cambrian invertebrates were trilobites. Scientists use many trilobites as index fossils to date rocks to the Cambrian Period.

30. Section 2 Precambrian Time and the Paleozoic Era Chapter 9 The Paleozoic Era, continued The Cambrian Period • The second most common animals of the Cambrian Period were the brachiopods, a group of shelled animals. • Fossils indicated that at least 15 different families of brachiopods existed during this period. • Other common Cambrian invertebrates include worms, jellyfish, snails, and sponges.

31. Section 2 Precambrian Time and the Paleozoic Era Chapter 9 The Paleozoic Era, continued Reading Check Name three common invertebrates from the Cambrian Period.

32. Section 2 Precambrian Time and the Paleozoic Era Chapter 9 The Paleozoic Era, continued Reading Check Name three common invertebrates from the Cambrian Period. Your answer should include three of the following: brachiopods, trilobites, jellyfish, worms, snails, and sponges.

33. Section 2 Precambrian Time and the Paleozoic Era Chapter 9 The Paleozoic Era, continued The Ordovician Period • During this period, populations of trilobites began to shrink, and clamlike brachiopods and cephalopod mollusks became the dominant invertebrate life-form. • Colonies of graptolites also flourished in the oceans, and the first vertebrates appeared. • The most primitive vertebrates were fish, which did not have jaws or teeth and were covered with thick, bony plates.

34. Section 2 Precambrian Time and the Paleozoic Era Chapter 9 The Paleozoic Era, continued The Silurian Period • During the Silurian Period, echinoderms, relatives of modern sea stars, and corals became more common. • Scorpion-like sea creatures called eurypterids also existed during this period. • Near the end of this period, the earliest land plants as well as animals evolved on land.

35. Section 2 Precambrian Time and the Paleozoic Era Chapter 9 The Paleozoic Era, continued The Devonian Period • The Devonian Period is called the Age of Fishes because fossils of many bony fishes were discovered in rocks of this period. • On type of fish, called a lungfish, had the ability to breathe air. Another type of fish, Rhipidistians, were air-breathing fish that had strong fins that may have allowed them to crawl onto the land for short periods of time. • Land plants, such as giant horsetails, ferns, and cone-bearing plants also began to develop during this period.

36. Section 2 Precambrian Time and the Paleozoic Era Chapter 9 The Paleozoic Era, continued The Carboniferous Period • In North America, the Carbiniferous Period is divided into the Mississippian and Pennsylvanian Periods. • During this time, the climate was warm, and forests and swamps covered most of the world. • Amphibians and fish continued to flourish, and the first vertebrates that were adapted to live on land appeared.

37. Section 2 Precambrian Time and the Paleozoic Era Chapter 9 The Paleozoic Era, continued The Permian Period • The Permian Period marks the end of the Paleozoic Era, because a mass extinction of a several life-forms occurred at the end of this period. • During this time, the continents had joined to form Pangaea, and as a result, the seas that covered the world retreated. • As the seas retreated, several species of marine life became extinct. But, reptiles and amphibians survived the environmental changes.

38. Section 3 The Mesozoic and Cenozoic Eras Chapter 9 Objectives • Listthe periods of the Mesozoic and Cenozoic Eras. • Identifytwo major geologic and biological developments during the Mesozoic Era. • Identifytwo major geologic and biological developments during the Cenozoic Era.

39. Section 3 The Mesozoic and Cenozoic Eras Chapter 9 The Mesozoic Era mass extinctionan episode during which large numbers of species become extinct Mesozoic Erathe geologic era that lasted from 251 million to 65.5 million years ago; also called the Age of Reptiles. • Earth’s surface changed dramatically during the Mesozoic Era. Pangaea broke into smaller continents, and the climate was warm and humid. • Lizards, turtles, snakes and dinosaurs flourished during this era.

40. Section 3 The Mesozoic and Cenozoic Eras Chapter 9 The Mesozoic Era, continued

41. Section 3 The Mesozoic and Cenozoic Eras Chapter 9 The Mesozoic Era, continued The Triassic Period • The Mesozoic Era is known as the Age of Reptiles and is divided into three periods: the Triassic, the Jurassic, and the Cretaceous Periods. • The Triassic period marked the appearance of dinosaurs. Most dinosaurs were about 4 m to 5 m long and moved very quickly. • Reptiles called ichthyosaurs lived in the oceans. The ammonite, a marine invertebrate, was dominant, and serves as a Mesozoic index fossil.

42. Section 3 The Mesozoic and Cenozoic Eras Chapter 9 The Mesozoic Era, continued The Jurassic Period • Two major groups of dinosaurs evolved during the Jurassic Period: the saurischians, or “lizard-hipped” dinosaurs, and the ornithischians, or “bird-hipped” dinosaurs. • Brontosauruses, now called Apatosauruses were saurischians. Stegosauruses and Pterosaurs were ornithischians.

43. Section 3 The Mesozoic and Cenozoic Eras Chapter 9 The Mesozoic Era, continued Reading Check Name two fossils that were discovered in the fossil record of the Jurassic Period.

44. Section 3 The Mesozoic and Cenozoic Eras Chapter 9 The Mesozoic Era, continued Reading Check Name two fossils that were discovered in the fossil record of the Jurassic Period. Your answer could include any two of the following: Archaeopteryx, pterosaurs, Apatosaurus, and Stegosaurus

45. Section 3 The Mesozoic and Cenozoic Eras Chapter 9 The Mesozoic Era, continued The Cretaceous Period • Among the common Cretaceous dinosaurs were the Tyrannosaurus Rex, the ankylosaurs, the ceratopsians, and the hadrosaurs. • The earliest flowering plants, or angiosperms, appeared during this period. The most common of these plants were magnolias and willows. • Later, trees such as maples, oaks, and walnuts became abundant.

46. Section 3 The Mesozoic and Cenozoic Eras Chapter 9 The Mesozoic Era, continued The Cretaceous-Tertiary Mass Extinction • The Cretaceous Period ended in another mass extinction. No dinosaur fossils have been found in rocks that formed after the Cretaceous Period. • Many scientists accept the impact hypothesis as the explanation for the extinction of the dinosaurs. This hypothesis is that about 65 million years ago, a giant meteorite crashed into Earth. • The impact of the collision raised enough dust to block the sun’s rays for many years, resulting in a colder climate that caused plant life to die and many animal species to become extinct.

47. Section 3 The Mesozoic and Cenozoic Eras Chapter 9 Mass Extinction

48. Section 3 The Mesozoic and Cenozoic Eras Chapter 9 The Cenozoic Era Cenozoic Erathe current geologic era, which began 65.5 million years ago; also called the Age of Mammals • During the Cenozoic Era, dramatic changes in climate have occurred. As temperatures decreased during the ice ages, new species that were adapted to life in cooler climates appeared. • Mammals became the dominant life-form and underwent many changes. • The Cenozoic Era is divided into two periods: the Tertiary Period and the Quaternary Period.

49. Section 3 The Mesozoic and Cenozoic Eras Chapter 9 The Cenozoic Era, continued The Quaternary and Tertiary Periods • The Tertiary Period includes the time before the last ice age, and is divided into five epochs: The Paleocene, Eocene, Oligocene, Miocene, and Pliocene Epochs. • The Quaternary Period began with the last ice age and includes the present. • The Quaternary is divided into two epochs: The Pleistocene and Holocene Epochs.

50. Section 3 The Mesozoic and Cenozoic Eras Chapter 9 The Cenozoic Era, continued The Paleocene and Eocene Epochs • The fossil record indicates that during the Paleocene Epoch many new mammals, such as small rodents, evolved. • Other mammals, including the earliest known ancestor of the horse, first whales, flying squirrels, and bats, evolved during this time. • Worldwide, temperatures dropped by about 4ºC at the end of the Eocene Epoch.