1. Minerals, Rocks, and the Fossil Record

2. SES1. Students will investigate the composition and formation of Earth systems, including the Earth’s relationship to the solar system. c. Describe how the decay of radioactive isotopes is used to determine the age of rocks, Earth, and solar system. e. Identify the transformations and major reservoirs that make up the rock cycle, hydrologic cycle, carbon cycle, and other important geochemical cycles. SES2. Students will understand how plate tectonics creates certain geologic features, materials, and hazards. d. Associate specific plate tectonic settings with the production of particular groups of igneous and metamorphic rocks and mineral resources. SES4. Students will understand how rock relationships and fossils are used to reconstruct the Earth’s past. a. Describe and apply principles of relative age (superposition, original horizontality, cross- cutting relations, and original lateral continuity) and describe how unconformities form. b. Interpret the geologic history of a succession of rocks and unconformities. c. Apply the principle of uniformitarianism to relate sedimentary rock associations and their fossils to the environments in which the rocks were deposited. d. Explain how sedimentary rock units are correlated within and across regions by a variety of methods (e.g., geologic map relationships, the principle of fossil succession, radiometric dating, and paleomagnetism). e. Use geologic maps and stratigraphic relationships to interpret major events in Earth history (e.g., mass extinction, major climatic change, tectonic events). SES6. Students will explain how life on Earth responds to and shapes Earth systems. d. Describe how fossils provide a record of shared ancestry, evolution, and extinction that is best explained by the mechanism of natural selection.

3. Chapter 5

4. Minerals of Earth’s Crust Chapter 5 SES2d. Associate specific plate tectonic settings with the production of particular groups of igneous and metamorphic rocks and mineral resources SES3d. Explain the processes that transport and deposit material in terrestrial and marine sedimentary basins, which result, over time, in sedimentary rock.

5. Section 1 What Is a Mineral? Chapter 5 To be a mineral, a substance must have four characteristics:  it must be inorganic—it cannot be made of or by living things;  it must occur naturally—it cannot be man-made;  it must be a crystalline solid;  it must have a consistent chemical composition.

6. Section 1 What Is a Mineral? Chapter 5  The 20 most common minerals are called rock- forming minerals because they form the rocks that make up Earth’s crust.  Ten minerals are so common that they make up 90% of Earth’s crust.  These minerals are quartz, orthoclase, plagioclase, muscovite, biotite, calcite, dolomite, halite, gypsum, and ferromagnesian minerals.  All minerals can be classified into two main groups—silicate minerals and nonsilicate minerals—based on their chemical compositions.

7. Section 1 What Is a Mineral? Chapter 5 Silicate Minerals  silicate mineral a mineral that contains a combination of silicon and oxygen, and that may also contain one or more metals  Common silicate minerals include quartz, feldspars, micas,and ferromagnesian minerals, such as amphiboles, pyroxenes, and olivines.  Silicate minerals make up 96% of Earth’s crust. Quartz and feldspar alone make up more than 50% of the crust.

8. Section 1 What Is a Mineral? Chapter 5 Nonsilicate Minerals  nonsilicate mineral a mineral that does not contain compounds of silicon and oxygen  Nonsilicate minerals comprise about 4% of Earth’s crust.  Nonsilicate minerals are organized into six major groups based on their chemical compositions.  The six major groups of nonsilicate minerals are carbonates, halides, native elements, oxides, sulfates, and sulfid es.

9. Section 1 What Is a Mineral? Chapter 5  Each type of mineral is characterized by a specific geometric arrangement of atoms, or its crystalline structure.  crystal a solid whose atoms, ions, or molecules are arranged in a regular, repeating pattern  One way that scientists study the structure of crystals is by using X rays. X rays that pass through a crystal and strike a photographic plate produce an image that shows the geometric arrangement of the atoms in the crystal.

10. Section 1 What Is a Mineral? Chapter 5  Even though there are many kinds of silicate minerals, their crystalline structure is made up of the same basic building blocks—silicon-oxygen tetrahedra.  silicon-oxygen tetrahedron the basic unit of the structure of silicate minerals; a silicon ion chemically bonded to and surrounded by four oxygen ions Isolated Tetrahedral Silicates  In minerals that have isolated tetrahedra, only atoms other than silicon and oxygen atoms like silicon-oxygen tetrahedra together.  Olivine is an isolated tetrahedral silicate.

11. Section 1 What Is a Mineral? Chapter 5 The diagram below shows the tetrahedral arrangement of isolated tetrahedral silicate minerals.

12. Section 1 What Is a Mineral? Chapter 5 Ring Silicates  Ring silicates form when shared oxygen atoms join the tetrahedra to form three-, four-, or six-sided rings.  Beryl and tourmaline are ring silicates. Single-Chain Silicates  In single-chain silicates, each tetrahedron is bonded to two others by shared oxygen atoms.  Most double-chain silicates are called pyroxenes.

13. Section 1 What Is a Mineral? Chapter 5 The diagram below shows the tetrahedral arrangement of ring silicate minerals.

14. Section 1 What Is a Mineral? Chapter 5 The diagram below shows the tetrahedral arrangement of single-chain silicate minerals.

15. Section 1 What Is a Mineral? Chapter 5 Double-Chain Silicates  In double-chain silicates, two single chains of tetrahedra bond to each other.  Most double-chain silicates are called amphiboles. Sheet Silicates  In the sheet silicates, each tetrahedron shares three oxygen atoms with other tetrahedra. The fourth oxygen atom bonds with an atom of aluminum or magnesium, which joins the sheets together.  The mica minerals, such as muscovite and biotite, are sheet silicates.

16. Section 1 What Is a Mineral? Chapter 5 The diagram below shows the tetrahedral arrangement of double- chain silicate minerals.

17. Section 1 What Is a Mineral? Chapter 5 The diagram below shows the tetrahedral arrangement of sheet silicate minerals.

18. Section 1 What Is a Mineral? Chapter 5 Framework Silicates  In the framework silicates, each tetrahedron is bonded to four neighboring tetrahedra to form a three- dimensional network.  Frameworks that contain only silicon-oxygen tetrahedra are the mineral quartz.  Other framework silicates contain some tetrahedra in which atoms of aluminum or other metals substitute for some of the silicon atoms.  Quartz and feldspars are framework silicates.

19. Section 1 What Is a Mineral? Chapter 5 The diagram below shows the tetrahedral arrangement of framework silicate minerals.

20. Section 1 What Is a Mineral? Chapter 5  Because nonsilicate minerals have diverse chemical compositions, nonsilicate minerals display a vast variety of crystalline structures.  Common crystalline structures for nonsilicate minerals include cubes, hexagonal prisms, and irregular masses.  The structure of a nonsilicate crystal determines the mineral’s characteristics.  In the crystal structure called closest packing, each metal atom is surrounded by 8 to 12 other metal atoms that are as close to each other as the charges of the atomic nuclei will allow.

21. Section 2 Identifying Minerals Chapter 5 Color  While color is a property that is easily observed, it is unreliable for the identification of minerals.  The color of a mineral sample can be affected by the inclusion of impurities or by weathering processes. Streak  streak the color of a mineral in powdered form  Streak is more reliable than color for the identification of minerals.  Streak is determined by rubbing some of the mineral against an unglazed ceramic tile called a streak plate.

22. Section 2 Identifying Minerals Chapter 5 Luster  luster the way in which a mineral reflects light  A mineral is said to have a metallic luster if the mineral reflects light as a polished metal does.  All other minerals have nonmetallic luster.  There are several types of nonmetallic luster, including glassy, waxy, pearly, brilliant, and earthy.

23. Section 2 Identifying Minerals Chapter 5 Cleavage and Fracture  cleavage in geology, the tendency of a mineral to split along specific planes of weakness to form smooth, flat surfaces  fracture the manner in which a mineral breaks along either curved or irregular surfaces  Uneven or irregular fractures have rough surfaces.  Splintery or fibrous fractures look like a piece of broken wood.  Curved surfaces are conchoidal fractures.

24. Section 2 Identifying Minerals Chapter 5 Hardness  The measure of the ability of a mineral to resist scratching is called hardness. Hardness does not mean “resistance to cleavage or fracture.”  The hardness of a mineral can be determined by comparing the mineral to minerals of Mohs hardness scale.  Mohs hardness scale the standard scale against which the hardness of minerals is rated.  The strength of the bonds between the atoms that make up a mineral’s internal structure determines the hardness of a mineral.

25. Section 2 Identifying Minerals Chapter 5 The diagram below shows Mohs Hardness Scale.

26. Section 2 Identifying Minerals Chapter 5 Density  density the ratio of the mass of a substance to the volume of a substance; commonly expressed as grams per cubic centimeter for solids  The density of a mineral depends on the kinds of atoms in the mineral and on how closely the atoms are packed. density = mass  volume

27. Section 2 Identifying Minerals Chapter 5  A few minerals have some additional, special properties that can help identify those minerals. Fluorescence and Phosphorescence  The ability to glow under ultraviolet light is called fluorescence.  Fluorescent minerals absorb ultraviolet light and then produce visible light of various colors.  The property of some minerals to glow after the ultraviolet light is turned off is called phosphorescence.

28. Section 2 Identifying Minerals Chapter 5 Chatoyancy and Asterism  In reflected light, some minerals display a silky appearance that is called chatoyancy, or the cat’s-eye effect.  A similar effect called asterism is the phenomenon in which a six-sided star appears when a mineral reflects light. Double Refraction  The property of some minerals, particularly some forms of calcite, to produce a double image of any object viewed through the mineral is called double refraction.

29. Section 2 Identifying Minerals Chapter 5 Magnetism  Minerals that are attracted to magnets display the property of magnetism. These minerals may be magnetic themselves.  In general, nonsilicate minerals that contain iron are more likely to be magnetic than silicate minerals are. Radioactivity  The property known as radioactivity results as unstable nuclei decay over time into stable nuclei by releasing particles and energy.  A Geiger counter is used to detect the released particles and, thus, to identify minerals that are radioactive.

30. Chapter 6

31.  SES2d. Associate specific plate tectonic settings with the production of particular groups of igneous and metamorphic rocks and mineral resources  SES3e. Explain the processes that transport and deposit material in terrestrial and marine sedimentary basins, which result, over time, in sedimentary rock.

32.  The material that makes up the solid parts of Earth is known as rock.  Made of a mixture of minerals and organic material.  Based on the processes that form and change the rocks of Earth’s crust, geologists classify rocks into three major types by the way the rocks form.

33.  All rock has physical and chemical properties that are determined by how and where the rock formed.  The rate at which rock weathers and the way that rock breaks apart are determined by the chemical stability of the minerals in the rock.  The rate at which mineral chemically breaks down is dependent on the chemical stability of the mineral.  Rocks have natural zones of weakness that are determined by how and where the rocks form..

34.  Igneous rock forms when magma, or molten rock, cools and hardens.  Sedimentary rock forms when sediment deposits that form when rocks, mineral crystals, and organic matter have been broken into fragments, called sediments, are compressed or cemented together.  Metamorphic rock forms when existing rock is altered by changes in temperature, by changes in pressure, or by chemical processes.

35.  Any of the three major types of rock can be changed into another of the three types.  Geologic forces and processes cause rock to change from one type to another.  rock cycle the series of processes in which rock forms, changes from one form to another, is destroyed, and forms again by geological processes

37.  Igneous rocks are classified according to where magma cools and hardens.  intrusive igneous rock rock formed from the cooling and solidification of magma beneath Earth’s surface  extrusive igneous rock rock formed from the cooling and solidification of lava at Earth’s surface  The texture of igneous rock is determined by the size of the crystals in the rock. The size of the crystals in determined mainly by the cooling rate of the magma.

38. Coarse-Grained Igneous Rock  Because intrusive igneous rocks cool slowly, they commonly have large mineral crystals.  Igneous rocks that are composed of large, well-developed mineral grains are described as having a coarse-grained texture. Fine-Grained Igneous Rock  Because extrusive igneous rocks cool rapidly, they are commonly composed of small mineral grains.  Igneous rocks that are composed of small crystals are described as having a fine-grained texture.

39.  Pumice rocks are igneous rocks which were formed when lava cooled quickly above ground. You can see where little pockets of air had been. This rock is so light, that many pumice rocks will actually float in water. Pumice is actually a kind of glass and not a mixture of minerals. Because this rock is so light, it is used quite often as a decorative landscape stone. Ground to a powder, it is used as an abrasive in polish compounds and in Lava© soap.

40.  Granite rocks are igneous rocks which were formed by slowly cooling pockets of magma that were trapped beneath the earth's surface. Granite is used for long lasting monuments and for trim and decoration on buildings.

41.  Scoria rocks are igneous rocks which were formed when lava cooled quickly above ground. You can see where little pockets of air had been. Scoria is actually a kind of glass and not a mixture of minerals.

42.  Obsidian rocks are igneous rocks that form when lava cools quickly above ground. Obsidian is actually glass and not a mixture of minerals. The edges of this rock are very sharp.

43.  Most sedimentary rock is made up of combinations of different types of sediment, which is loose fragments of rock, minerals, and organic materials.  Two main processes convert loose sediment into sedimentary rock—compaction and cementation.  compaction the process in which the volume and porosity of a sediment is decreased by the weight of overlying sediments as a result of burial beneath other sediments  cementation the process in which minerals precipitate into pore spaces between sediment grains and bind sediments together to form rock

44.  Geologists classify sedimentary rocks by the processes by which the rocks form and by the composition of the rocks.  There are three main classes of sedimentary rocks—chemical, organic, and clastic.  These three classes contain their own classifications of rocks that are grouped based on the shape, size, and composition of the sediments that form the rocks.

45.  chemical sedimentary rock sedimentary rock that forms when minerals precipitate from a solution or settle from a suspension  Some chemical sedimentary rock forms when dissolved minerals precipitate out of water because of changing concentrations of chemicals.  When water evaporates, the minerals that were dissolved in the water are left behind. Eventually, the concentration of minerals in the remaining water becomes high enough to cause minerals to precipitate out of the water.  Rocks that form through evaporation are called evaporites. Gypsum and halite are common evaporites.

46.  Gypsum rocks are sedimentary rocks made up of sulfate mineral and formed as the result of evaporating sea water in massive prehistoric basins. It is very soft and is used to make Plaster of Paris, casts, molds, and wallboards.

47.  organic sedimentary rock sedimentary rock that forms from the remains of plants or animals  Coal and some limestones are examples of organic rocks.  Organic limestones form when marine organisms, such as coral, clams, oysters, and plankton, remove the chemical components of the minerals calcite and aragonite from sea water.  The organisms make their shells from these minerals, and when the organisms die, their shells settle to the bottom of the ocean, accumulate, and are compacted to form limestone.

48. Section 3 Sedimentary Rock Chapter 6 The diagram below shows the formation of organic limestone.

49.  Limestone rocks are sedimentary rocks that are made from the mineral calcite which came from the beds of evaporated seas and lakes and from sea animal shells. This rock is used in concrete and is an excellent building stone for humid regions.

50.  clastic sedimentary rock sedimentary rock that forms when fragments of preexisting rocks are compacted or cemented together  Clastic sedimentary rocks are classified by the size of the sediments they contain.  Rock that contains large, rounded pieces is called conglomerate. Rock that contains large, angular pieces is called breccia.  Rock that is composed of sand-sized grains is called sandstone. Rock that is composed of clay-sized particles is called shale.

51.  The physical characteristics of sediments are determined mainly by the way sediments were transported to the place where they are deposited.  Sediments are transported by four main agents: water, ice, wind, and the effects of gravity.

52.  Conglomerate rocks are sedimentary rocks. They are made up of large sediments like sand and pebbles. The sediment is so large that pressure alone cannot hold the rock together; it is also cemented together with dissolved minerals.

53.  Sandstone rocks are sedimentary rocks made from small grains of the minerals quartz and feldspar. They often form in layers as seen in this picture. They are often used as building stones.

54.  Shale rock is a type of sedimentary rock formed from clay that is compacted together by pressure. They are used to make bricks and other material that is fired in a kiln.

55.  metamorphism the process in which one type of rock changes into metamorphic rock because of chemical processes or changes in temperature and pressure  During metamorphism, heat, pressure, and hot fluids cause some minerals to change into other minerals.  Minerals may also change in size or shape, or they may separate into parallel bands that give the rock a layered appearance.  Hot fluids may circulate through the rock and change the mineral composition of the rock by dissolving some materials and by adding others.

56.  The type of rock that forms because of metamorphism can indicate the conditions under which the original rock changed.  The composition of the rock being metamorphosed, the amount and direction of pressure, and the presence or absence of certain fluids cause different combinations of minerals to form.  Two types of metamorphism occur in Earth’s crust— contact metamorphism and regional metamorphism.

57. Contact Metamorphism  contact metamorphism a change in the texture, structure, or chemical composition of a rock due to contact with magma Regional Metamorphism  regional metamorphism a change in the texture, structure, or chemical composition of a rock due to changes in temperature and pressure over a large area, generally are a result of tectonic forces

58. Foliated Rocks  foliation the metamorphic rock texture in which minerals grains are arranged in planes or bands  Extreme pressure may cause the mineral crystals in the rock to realign or regrow to form parallel bands.  Foliation also occurs as minerals that have different compositions separate to produce a series of alternating dark and light bands.  Foliated metamorphic rocks include the common rocks slate, schist, and gneiss.

59.  Gneiss rocks are metamorphic. These rocks may have been granite, which is an igneous rock, but heat and pressure changed it. You can see how the mineral grains in the rock were flattened through tremendous heat and pressure and are arranged in alternating patterns.

60.  Schist rocks are metamorphic. These rocks can be formed from basalt, an igneous rock; shale, a sedimentary rock; or slate, a metamorphic rock. Through tremendous heat and pressure, these rocks were transformed into this new kind of rock.

61. Nonfoliated Rocks  nonfoliated the metamorphic rock texture in which minerals grains are not arranged in planes or bands  Many nonfoliated metamorphic rocks contain grains of only one mineral or contain very small amounts of other minerals. Thus, the rock does not form bands of different minerals.  Other nonfoliated metamorphic rocks contain grains that are round or square. These grains are unlikely to change shape or position when exposed to directed pressure.  Nonfoliated metamorphic rocks include the common rocks marble and quartzite.

62.  The three factors that affect whether rock melts include temperature, pressure, and the presence of fluids in the rock.

63. Chapter 8

64. SES1. Students will investigate the composition and formation of Earth systems, including the Earth’s relationship to the solar system. c. Describe how the decay of radioactive isotopes is used to determine the age of rocks, Earth, and solar system. SES4. Students will understand how rock relationships and fossils are used to reconstruct the Earth’s past. a. Describe and apply principles of relative age (superposition, original horizontality, cross-cutting relations, and original lateral continuity) and describe how unconformities form. b. Interpret the geologic history of a succession of rocks and unconformities. c. Apply the principle of uniformitarianism to relate sedimentary rock associations and their fossils to the environments in which the rocks were deposited. d. Explain how sedimentary rock units are correlated within and across regions by a variety of methods (e.g., geologic map relationships, the principle of fossil succession, radiometric dating, and paleomagnetism). e. Use geologic maps and stratigraphic relationships to interpret major events in Earth history (e.g., mass extinction, major climatic change, tectonic events). SES6. Students will explain how life on Earth responds to and shapes Earth systems. d. Describe how fossils provide a record of shared ancestry, evolution, and extinction that is best explained by the mechanism of natural selection.

65. uniformitarianism a principle that geologic processes that occurred in the past can be explained by current geologic processes  Geologists estimate that Earth is about 4.6 billion years old, an idea that was first proposed by James Hutton in the 18th century.  Hutton theorized that the same forces that change Earth’s surface now, such as volcanism and erosion, are the same forces that were at work in the past.

66. relative age the age of an object in relation to the ages of other objects  One way to learn about Earth’s past is to determine the order in which rock layers and other rock structures formed.  Layers of rock, called strata, show the sequence of events that took place in the past.  Once they know the order, a relative age can be determined for each layer.  Relative age indicated that one layer is older or younger than another layer but does not indicate the rock’s age in years.

67. law of superposition the law that a sedimentary rock layer is older than the layers above it and younger than the layers below it if the layers are not disturbed  Scientists commonly study the layers in sedimentary rocks to determine the relative age of rocks.  Sedimentary rocks form when new sediments are deposited on top of old layers of sediment.  As the sediments accumulate, they harden into layers called beds. The boundary between two beds is called a bedding plane.  Scientists use a basic principle called the law of superposition to determine the relative age of a layer of sedimentary rock.

68. The diagram below illustrates the law of Superposition.

69.  Scientist know that sedimentary rock generally forms in horizontal layers.  The principle of original horizontality states that sedimentary rocks left undisturbed will remain in horizontal layers.  So, scientists can assume that sedimentary rock layers that are not horizontal have been tilted or deformed by crustal movements that happened after the layers formed.

70. unconformity a break in the geologic record created when rock layers are eroded or when sediment is not deposited for a long period of time.

71. law of crosscutting relationships the principle that a fault or body of rock is younger than any other body of rock that it cuts through.

72. absolute age the numeric age of an object or event, often stated in years before the present, as established by an absolute-dating process, such as radiometric dating  Scientists use a variety of ways to determine absolute age, or the numeric age, of a rock formation.

73. Rates of Erosion  One way scientists use to estimate absolute age is to study rates of erosion.  Studying the rates of erosion is practical only for geologic features that formed within the past 10,000 to 20,000 years.  For older surface features, the method is less dependable because rates of erosion can vary over millions of years.

74. Rates of Deposition  Scientists can also estimate absolute age by calculating the rate of sediment deposition.  By using data collected over a long period of time, geologists can estimate the average rates of deposition for common sedimentary rocks.  This method is not always accurate because not all sediment is deposited at an average; therefore it provides only an estimate of absolute age.

75. Varve Count varve a banded layer of sand and silt that is deposited annually in a lake, especially near ice sheets or glaciers, and that can be used to determine absolute age.  Some sedimentary deposits show definite annual layers, called varves.  The varves can be counted much like tree rings to determine the age of the sedimentary deposit.

76. radiometric dating a method of determining the absolutes age of an object by comparing the relative percentages of a radioactive (parent) isotope and a stable (daughter) isotope.  Rocks generally contain small amounts of radioactive material that can act as natural clocks.  Atoms of the same element that have different numbers of neutrons are called isotopes.  Radioactive isotopes can be used to determine age.

77.  Radioactive isotopes have nuclei that emit particles and energy at a constant rate regardless of surrounding conditions.  Scientists use the natural breakdown of isotopes to accurately measure the absolute age of rock, which is called radiometric dating.  To do this, scientists measure the concentration of the parent isotope or original isotope, and of the newly formed daughter isotopes. Then, using the known decay rate, they can determine the absolute age of the rock.

78. half-life the time required for half of a sample of a radioactive isotope to break down by radioactive decay to form a daughter isotope.  Scientists have determined that the time required for half of any amount of a particular radioactive isotope to decay is always the same and can be determined for any isotope.  By comparing the amounts of parent and daughter isotopes in a rock sample, scientists can determine the age of the sample.  The greater the percentage of daughter isotopes present in the sample, the older the rock is.

80. Radioactive Isotopes  Uranium-238, or 238 U, is an isotope of uranium that has an extremely long half-life, and is most useful for dating geologic samples that are more than 10 million years old.  Potassium-40, or 40 K, has a half-life of 1.25 billion years, and is used to date rock that are between 50,000 and 4.6 billion years old.  Rubidium-87 has a half-life of about 49 billion years, and is used to verify the age of rocks previously dated by using 40 K.

81. Carbon Dating  Younger rock layers may be dated indirectly by dating organic material found within the rock.  Organic remains, such as wood, bones, and shells that are less than 70,000 years old can be determined by using a method known as carbon-14 dating, or radiocarbon dating.  All living organisms have both the carbon-12 and carbon- 14 isotope.  To find the age of a sample of organic material, scientists compare the ratio of 14 C to 12 C and then compare this with the ratio of 14 C to 12 C known to exist in a living organism.  Once a plant or animal dies, the ratio begins to change, and scientist can determine the age from the difference between the ratios of 14 C to 12 C in the dead organism.

82. fossils the trace or remains of an organism that lived long ago, most commonly preserved in sedimentary rock paleontology the scientific study of fossils  Fossils are an important source of information for finding the relative and absolute ages of rocks.  Fossils also provide clues to past geologic events, climates, and the evolution of living things over time.

83.  Almost all fossils are discovered in sedimentary rock.  The fossil record provides information about the geologic history of Earth.  Scientists can use this information to learn about how environmental changes have affected living organisms.

84.  Only dead organisms that are buried quickly or protected from decay can become fossils.  Generally only the hard parts of organisms, such as wood, bones, shells, and teeth, become fossils.  In rare cases, an entire organism may be preserved.  In some types of fossils, only a replica of the original organism remains. Others merely provide evidence that life once existed.

85. Mummification  Mummified remains are often found in very dry places, because most bacteria which cause decay cannot survive in these places.  Some ancient civilizations mummified their daed by carefully extracting the body’s internal organs and then wrapping the body in carefully prepared strips of cloth.

86. Amber  Hardened tree sap is called amber. Insects become trapped in the sticky sap and are preserved when the sap hardens.  In many cases, delicate features such as legs and antennae have been preserved. In rare cases, DNA has been recovered from amber.

87. Tar Seeps  When thick petroleum oozes to Earth’s surface, the petroleum forms a tar seep.  Tar seeps are commonly covered by water. Animals that come to drink the water can become trapped in the sticky tar.  The remains of the trapped animals are covered by the tar and preserved.

88. Freezing  The low temperatures of frozen soil and ice can protect and preserve organisms.  Because most bacteria cannot survive freezing temperatures, organisms that are buried in frozen soil or ice do not decay.

89. Petrification  Mineral solutions such as groundwater replace the original organic materials that were covered by layers of sediment with new materials.  Some common petrifying minerals are silica, calcite, and pyrite.  The substitution of minerals for organic material other results in the formation of a nearly perfect mineral replica of the original organism.

90. trace fossil a fossilized mark that formed in sedimentary rock by the movement of an animal on or within soft sediment  In some cases, no part of the original organism survives in fossil form. But the fossilized evidence of past animal movement can still provide information about prehistoric life.  A trace fossils in an important clue to the animal’s appearance and activities.

91. Imprints  Carbonized imprints of leaves, stems, flowers, and fish made in soft mud or clay have been found preserved in sedimentary rock.  When original organic material partially decays, it leaves behind a carbon-rich film. An imprint displays the surface features of the organism.

92. Molds and Casts  Shells often leave empty cavities called molds within hardened sediment. When a shell is buried, its remains eventually decay and leave an empty space.  When sand or mud fills a mold and hardens, a natural cast forms.  A cast is a replica of the original organism.

93. Coprolites  Fossilized dung or waste materials from ancient animals are called coprolites.  They can be cut into thin sections and observed through a microscope. The materials identified in these sections reveal the feeding habits of ancient animals, such as dinosaurs.

94. Gastroliths  Some dinosaurs had stones in their digestive systems to help grind their food. In many cases, these stones, which are called gastroliths, survives as fossils.  Gastroliths can often be recognized by their smooth, polished surfaces and by their close proximity to dinosaurs remains.

95. Index fossils  Index fossil a fossil that is used to establish the age of rock layers because it is distinct, abundant, and widespread and existed for only a short span of geologic time.  Paleontologists can use index fossils to determine the relative ages of the rock layers in which the fossils are located.  To be an index fossil, a fossil must be present in rocks scattered over a large region, and it must have features that clearly distinguish it from other fossils.  In addition, organisms from which the fossil formed must have lived during a short span of geologic time, and the fossil must occur in fairly large numbers within the rock layers.

96.  Scientists can use index fossils to estimate absolute ages of specific rock layers. Because organisms that formed index fossils lived during short spans of geologic time, the rock layer in which an index fossil was discovered can be dated accurately. Scientists can also use index fossils to date rock layers in separate area. Index fossils are used to help locate rock layers that are likely to contain oil and natural gas deposits.

97. Chapter 9

98. SES4. Students will understand how rock relationships and fossils are used to reconstruct the Earth’s past. a. Describe and apply principles of relative age (superposition, original horizontality, cross-cutting relations, and original lateral continuity) and describe how unconformities form. b. Interpret the geologic history of a succession of rocks and unconformities. c. Apply the principle of uniformitarianism to relate sedimentary rock associations and their fossils to the environments in which the rocks were deposited. d. Explain how sedimentary rock units are correlated within and across regions by a variety of methods (e.g., geologic map relationships, the principle of fossil succession, radiometric dating, and paleomagnetism). e. Use geologic maps and stratigraphic relationships to interpret major events in Earth history (e.g., mass extinction, major climatic change, tectonic events). SES6. Students will explain how life on Earth responds to and shapes Earth systems. d. Describe how fossils provide a record of shared ancestry, evolution, and extinction that is best explained by the mechanism of natural selection.

99. 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.  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.

100.  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.

102. Eons  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.

103. Eras era a 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.  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.

104. Periods and Epochs  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. period a unit of geologic time that is longer than an epoch but shorter than an era  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. epoch a subdivision of geologic time that is longer than an age but shorter than a period.  Epochs may be divided into smaller units of time called ages.  Ages are defined by the occurrence of distinct fossils in the fossil record.

105. 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  By examining rock layers and fossils, scientists have discovered evidence that species of livings things have changed over time.  Scientists call this process evolution.

106. 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.

108. 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.

110.  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.

111. 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.

112. 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.

113. 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.

114. 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.  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.

115. 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.

116. 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.

117. 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.

118. 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.

119. 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.

120. mass extinction an episode during which large numbers of species become extinct Mesozoic Era the 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.

122. 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.

123. 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.

124. 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.

125. 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.

126. Cenozoic Era the 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.

127. 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.

128. 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.

129. The Oligocene and Miocene Epochs  During these epochs, the worldwide climate became significantly cooler and drier. The modern Antarctic icecap began to form. The Mediterranean Sea dried up and refilled several times.  This climate change caused many early mammals to become extinct. However large species of deer, pigs, horses, camels, cats, and dogs flourished. Also, the climate change favored grasses, cone- bearing, and hardwood trees.

130. The Pliocene Epoch  During the Pliocene Epoch, animals such as bears, dogs, and cats, evolved into modern forms. Herbivores, such as the giant ground sloth, flourished.  Dramatic climatic changes occurred, and the continental ice sheets began to spread. The Bering land bridge and the Central American land bridge formed, allowing various species to migrate between the continents.

131. The Pleistocene Epoch  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.  Fossils of the earliest ancestors of modern humans were discovered in Pleistocene sediments.  Evidence of more-modern human ancestors indicated that early humans may have been hunters.

132. The Holocene Epoch  The Holocene Epoch began 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.  Modern humans developed agriculture and began to make and use tools made of bronze and iron.