1. Chapter 9 Table of Contents Section 1 Geologic Time
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

2. Chapter 9
Section 1 Geologic Time
Objectives
Summarize how scientists worked together to develop the geologic column.
List the major divisions of geologic time.

3. Chapter 9 The Geologic Column Section 1 Geologic Time
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.(6)(7)
Evidence of changing conditions on Earth’s surface is recorded in the rock layers of Earth’s crust.(1)
The geologic time scale describes the sequence and length of changes in earth’s crust. This outlines the development of Earth and of life on Earth.(2)(3)
No single area on Earth contained a record of all geologic time, so scientists combined observations to create a standard geologic column.(5)

4. The Geologic Column, continued
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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.(8)
Fossils in the upper layers resemble modern plants and animals.(9)
Many of the fossils discovered in older, lower layers are from species that look different from those living today and that have been extinct for millions of years.(9)(10)
19th century scientists studied fossils and applied the principle that old layers of rock are below young layers. (4)

5. The Geologic Column, continued
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Section 1 Geologic Time
The Geologic Column, continued
Using a Geologic Column
The first geologic columns developed used the average rates of sediment deposition. (11)
To accurately determine ages of rock layers, scientist now use radiometric dating. (12)
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. (13)
If the two layers match, they likely formed at about the same time.(14)

6. Divisions of Geologic Time
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. (15)
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. (16)

7. Divisions of Geologic Time, continued
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Section 1 Geologic Time
Divisions of Geologic Time, continued
The abbreviation Ma stands for millions of years ago. (18)
Answers for 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32,

8. Divisions of Geologic Time, continued
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.(33) (34)
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.(35)

9. Divisions of Geologic Time, continued
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Section 1 Geologic Time
Divisions of Geologic Time, continued
Eons and Eras
era a unit of geologic time that includes two or more periods(37)
Dividing Precambrian time into smaller units is difficult because very few fossils exist in early Precambrian rocks. (36)
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.(38)(39)

10. Divisions of Geologic Time, continued
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.(42)
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 65.5 million years ago. Fossils of mammals are common in Cenozoic rocks.(43)(44)(45)

11. Divisions of Geologic Time, continued
Chapter 9
Section 1 Geologic Time
Divisions of Geologic Time, continued
Eons and Eras
period a unit of geologic time that is longer than an epoch but shorter than an era, what epochs are divided into.
epoch a subdivision of geologic time that is longer than an age but shorter than a period, what periods are divided into. (48)
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.

12. Divisions of Geologic Time, continued
Chapter 9
Section 1 Geologic Time
Divisions of Geologic Time, continued
Eons and Eras
Where the rock record is incomplete and deformed, a detailed fossil record may be lacking to allow scientists to divide period into shorter time units called epochs. (49)
Epochs may be divided into smaller units of time called ages. (50)
Ages are defined by the occurrence of distinct fossils in the fossil record.(51)

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

14. Section 2 Precambrian Time and the Paleozoic Era
Chapter 9
Objectives
Summarize how evolution is related to geologic change.
Identify two characteristics of Precambrian rock.
Identify one major geologic and two major biological developments during the Paleozoic Era.

15. Chapter 9 Evolution Section 2 Precambrian Time and the Paleozoic Era
evolution an 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(3)
By examining rock layers and fossils, scientists have discovered where the geologic history was recorded and evidence that species of livings things have changed over time. (1)(6)
Scientists call this process evolution.
Information about the environment when the layer formed is the kind of information scientists get form types of rock and fossils in a rock layer. (2)

16. Chapter 9 Evolution, continued Evolution and Geologic Change
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. This theory was proposed in 1859 by Charles Darwin. (4)
Major geologic and climatic changes can affect the ability of some organisms to survive.(5)
By using geologic evidence, scientists try to determine how environmental changes affected organisms in the past.

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

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

19. Chapter 9 Precambrian Time
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.(8)(10)
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.(9)(11)(12)
A nebula is a large cloud or gases. (7)

20. Precambrian Time, continued
Section 2 Precambrian Time and the Paleozoic Era
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Precambrian Time, continued

21. Precambrian Time, continued
Section 2 Precambrian Time and the Paleozoic Era
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Precambrian Time, continued
The Precambrian rock record is difficult to interpret, because the rocks were damaged and therefore could not be identified, therefore we do not know much about what happened during that time. (13)
Most Precambrian rocks have been so severely deformed and altered by tectonic activity that the original order of rock layers is rarely identifiable.

22. Precambrian Time, continued
Section 2 Precambrian Time and the Paleozoic Era
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Precambrian Time, continued
Precambrian Rocks
Large areas of exposed Precambrian rocks, called shields, exist on every continent. Formed from volcanic activity, mountain building, sedimentation, and metamorphism.(14) (15)
Nearly half of the valuable mineral deposits in the world occur in the rocks of Precambrian shields.(16)
These valuable minerals include nickel, iron, gold, and copper.(17)

23. Precambrian Time, continued
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, rock were very old, and many fossils were probable destroyed as a result of volcanic activity, erosion, folding and faulting.(18)
One of the few Precambrian fossils that have been discovered are stromatolites, which are reeflike deposits formed by blue-green algae. They form in warm, shallow waters. (19)(20)
The presence of stromatolite fossils in Precambrian rocks indicates that shallow seas covered much of Earth during that time.(21)

24. Chapter 9 The Paleozoic Era
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.(22)(23)(24)
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.(28)

25. The Paleozoic Era, continued
When the Paleozoic Era began, Earth’s landmasses were scattered around the world. (25)
By the end of the Paleozoic Era, Earth’s landmasses had collided to form the supercontinent, Pangaea. (26)
Paleozoic rock contain many fossils, while Precambrian rocks do not. (27)

26. The Paleozoic Era, continued
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The Paleozoic Era, continued
The Cambrian Period
The Cambrian Period is the first period of the Paleozoic Era.
Land-dwelling plants and animals were not present. (35)
Marine invertebrates thrived in the warm waters that existed during this time.(30)
Invertebrates lack a backbone. (32)
The most common of the Cambrian invertebrates were trilobites. Scientists use many trilobites as index fossils to date rocks to the Cambrian Period.(34)

27. The Paleozoic Era, continued
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.(31)
Fossils indicated that at least 15 different families of brachiopods existed during this period.
Other common Cambrian invertebrates include worms, jellyfish, snails, and sponges.

28. The Paleozoic Era, continued
Section 2 Precambrian Time and the Paleozoic Era
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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.(37)
Colonies of tiny graptolites also flourished in the oceans, and the first vertebrates (animals with backbones) appeared. (36)(38)
The most primitive vertebrates were fish, which did not have jaws or teeth and were covered with thick, bony plates. (39)

29. The Paleozoic Era, continued
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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.(40)
Near the end of this period, the earliest land plants as well as animals evolved on land.(41)

30. The Paleozoic Era, continued
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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. (42)
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. (43)(45)
The first amphibians were Ichthyostega. (44)
Land plants, such as giant horsetails, ferns, and cone-bearing plants also began to develop during this period.(46)

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The Paleozoic Era, continued
The Carboniferous Period
Carboniferous mean carbon bearing. (49)
In North America, the Carboniferous Period is divided into the Mississippian and Pennsylvanian Periods.(50)
During this time, the climate was warm and humid, and forests and swamps covered most of the world.(47)(48)
Amphibians and fish continued to flourish, and the first vertebrates that were adapted to live on land appeared as large lizards.(52)
Crinoids, a type of sea lily, are thought to be modern ancestor of sea stars. (51)

32. The Paleozoic Era, continued
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.(53)(54)
During this time, the continents had joined to form Pangaea, and as a result, the seas that covered the world retreated.(55)
Areas of desert and dry savanna climates developed on the northwest side of mountains, and shallow inland seas disappeared. (56)
As the seas retreated, several species of marine life became extinct such as eurypterids and trilobites. But, reptiles and amphibians survived the environmental changes.(57)(58)

33. Section 3 The Mesozoic and Cenozoic Eras
Chapter 9
Objectives
List the periods of the Mesozoic and Cenozoic Eras.
Identify two major geologic and biological developments during the Mesozoic Era.
Identify two major geologic and biological developments during the Cenozoic Era.

34. Chapter 9 The Mesozoic Era Section 3 The Mesozoic and Cenozoic Eras
At the end of the Permian, 90% of marine organisms and 78% of land organisms died.(1)(2)
mass extinction an episode during which large numbers of species become extinct(3)
New life-forms appeared after the mass extinction due to readily available resources and space. (4)
Mesozoic Era the geologic era that lasted from 251 million to 65.5 million years ago; also called the Age of Reptiles.(5)(6)
Earth’s surface changed dramatically during the Mesozoic Era. Pangaea broke into smaller continents, and the climate was warm and humid and shallow seas and marshes covered much of the land. Collisions of tectonic plates formed mountain ranges. (7)(8)(9)
Lizards, turtles, snakes and dinosaurs flourished during this era.(10)

35. The Mesozoic Era, continued
Section 3 The Mesozoic and Cenozoic Eras
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The Mesozoic Era, continued

36. The Mesozoic Era, continued
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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.(11)(12)
Trees of the Triassic, called cycads, resembled today’s palm trees. (13)
The Triassic period marked the appearance of dinosaurs, the dominant life-form. Most dinosaurs were about 4 m to 5 m long and moved very quickly.(16)
Reptiles called ichthyosaurs lived in the oceans. The ammonite, a marine invertebrate, was dominant, and serves as a Mesozoic index fossil. (14)(15)

37. The Mesozoic Era, continued
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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.(17)(19)
Brontosauruses, now called Apatosauruses were saurischians and weighed up to 50 tons. Stegosauruses, one of the best known ornithischians and Pterosaurs were flying reptiles with skin-covered wings and were also ornithischians.(18)(20)(21)

38. The Mesozoic Era, continued
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The Mesozoic Era, continued
The Cretaceous Period
Among the common Cretaceous dinosaurs were the Tyrannosaurus Rex (6m tall with teeth up to 15 cm long), the armored ankylosaurs, the horned ceratopsians, and the duck-billed hadrosaurs.(22)(23)(24)(25)
The earliest flowering plants, or angiosperms, appeared during this period. The most common of these plants were magnolias and willows.(26)
Later, trees such as maples, oaks, and walnuts became abundant.

39. The Mesozoic Era, continued
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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.(27)
One theory for the extinction of dinosaurs is that the continents moved and there was increased volcanic activity that led to environmental changes. (28)
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, spreading iridium all over it.(28)(29)(30)
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.(28)

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

41. Chapter 9 The Cenozoic Era Section 3 The Mesozoic and Cenozoic Eras
Cenozoic Era the current geologic era, which began 65.5 million years ago and includes the present; also called the Age of Mammals(31)(32)
The earth’s continents moved to their present-day locations. (33)
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 and ice sheets covered one-third of Earth’s land at times.(34)
Mammals became the dominant life-form and underwent many changes due to the cooler climates.(35)
The Cenozoic Era is divided into two periods: the Tertiary Period and the Quaternary Period.

42. The Cenozoic Era, continued
Section 3 The Mesozoic and Cenozoic Eras
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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.(36)(38)
The Quaternary Period began with the last ice age and includes the present. (37)
The Quaternary is divided into two epochs: The Pleistocene and Holocene Epochs.(39)

43. The Cenozoic Era, continued
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 and primates, evolved.(40)
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.(41)
The Himalayas were uplifted due to the collision of the Indian subcontinent with the Eurasian continent. (42)

44. The Cenozoic Era, continued
Section 3 The Mesozoic and Cenozoic Eras
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The Cenozoic Era, continued
The Oligocene and Miocene Epochs
During these epochs, the worldwide climate became significantly cooler and drier. The modern Antarctic icecap began to form and circumpolar currents formed around Antarctica. The Mediterranean Sea dried up and refilled several times.(43)(44)
This climate change caused many early mammals to become extinct. However largest known species of deer, pigs, horses, camels, cats, and dogs flourished. Also, the climate change favored grasses, cone-bearing, and hardwood trees. (43)(45)

45. The Cenozoic Era, continued
Section 3 The Mesozoic and Cenozoic Eras
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The Cenozoic Era, continued
The Pliocene Epoch
During the Pliocene Epoch, predatory animals such as bears, dogs, and cats, evolved into modern forms. Herbivores, such as the giant ground sloth, flourished.(46)
Dramatic climatic changes occurred, and the continental ice sheets began to spread. As a result, much of Earth’s water became locked in ice. The Bering land bridge and the Central American land bridge formed, allowing various species to migrate between the continents. (47)

46. The Cenozoic Era, continued
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The Cenozoic Era, continued
The Pleistocene Epoch
Began about 1.8 million years ago. (48)
During the Pleistocene Epoch, ice sheets in Europe and North America advanced and retreated several times.
Some animals had certain features that allowed them to survive the cold climate, such as the thick fur that covered woolly mammoths.
Other species survived by moving to warmer regions, while some species eventually became extinct.

47. The Cenozoic Era, continued
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The Cenozoic Era, continued
The Pleistocene Epoch
Fossils of the earliest ancestors of modern humans were discovered in Pleistocene sediments.(49)
Evidence of more-modern human ancestors indicated that early humans may have been hunters.

48. The Cenozoic Era, continued
Section 3 The Mesozoic and Cenozoic Eras
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The Cenozoic Era, continued
The Holocene Epoch
The Holocene Epoch began 11,500 years ago as the last glacial period ended. As the ice sheets melted, sea level rose about 140 m, and the coastlines took on their present shapes.(50)
Modern humans developed agriculture and began to make and use tools made of bronze and iron.
If the entire history of the earth is pictured as occurring in one year, the dinosaurs would have disappeared on December 26.(51)

49. The Geologic Time Scale
Chapter 9
The Geologic Time Scale

50. Similar Skeletal Structures of Mammals
Chapter 9
Similar Skeletal Structures of Mammals

51. Precambrian Time and the Paleozoic Era
Chapter 9
Precambrian Time and the Paleozoic Era

52. The Mesozoic and Cenozoic Era
Chapter 9
The Mesozoic and Cenozoic Era

53. Fossil Evidence for Gondwanaland
Chapter 9
Fossil Evidence for Gondwanaland