1. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu How to Use This Presentation To View the presentation as a slideshow with effects select “View” on the menu bar and click on “Slide Show.” To advance through the presentation, click the right-arrow key or the space bar. From the resources slide, click on any resource to see a presentation for that resource. From the Chapter menu screen click on any lesson to go directly to that lesson’s presentation. You may exit the slide show at any time by pressing the Esc key.

2. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Chapter Presentation Transparencies Image and Math Focus Bank Bellringers Standardized Test Prep CNN Videos Visual Concepts Resources

3. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Formation of the Solar System Section 1 A Solar System Is Born Section 2 The Sun: Our Very Own Star Section 3 The Earth Takes Shape Section 4 A Solar System is Born Chapter 20 Table of Contents

4. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Chapter 20 Bellringer Could astronauts land on a star in the same way that they landed on the moon? Explain why or why not. Write your answer in your science journal. Section 1 A Solar System Is Born

5. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Chapter 20 Explain the relationship between gravity and pressure in a nebula. Describe how the solar system formed. Objectives Section 1 A Solar System Is Born

6. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Chapter 20 Solar System The solar system includes: The sun and 8 planets Satellites orbiting the planets Thousands of asteroids: small rocky bodies that orbit the sun, most are between Mars and Jupiter Comets: small bodies of ice, rock, and cosmic dust loosely packed, heats the ice giving off gas and dust in the form of a long tail Section 1 A Solar System Is Born

7. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Chapter 20 The Solar Nebula All of the ingredients for building planets, moons, and stars are found in the vast, seemingly empty regions of space between the stars. Clouds called nebulas are found in these regions. A nebula is a large cloud of gas and dust in interstellar space Section 1 A Solar System Is Born

8. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Chapter 20 The Solar Nebula, continued Nebulas contain gases -- mainly hydrogen and helium -- and dust made of elements such as carbon and iron. These gases and elements interact with gravity and pressure to form stars and planets. Section 1 A Solar System Is Born

9. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Chapter 20 The Solar Nebula, continued In science, temperature is a measure of kinetic energy, which is energy in motion An increase in temperature causes particles to speed up, increasing collisions, which causes the particles to push away from each other, which causes pressure In a nebula, pressure pushes outward while gravitational attraction pushes inward. If these forces are in equilibrium, the nebula will not collapse; if it is upset, the nebula will not collapse Section 1 A Solar System Is Born

10. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Chapter 20 The Solar Nebula, continued Gravity Pulls Matter Together The gas and dust that make up nebulas are made of matter, which is held together by the force of gravity. Section 1 A Solar System Is Born Gravity causes the particles in a nebula to be attracted to each other.

11. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Chapter 20 The Solar Nebula, continued Pressure Pushes Matter Apart The relationship between temperature and pressure keeps nebulas from collapsing. Temperature is a measure of the average kinetic energy, or energy of motion, of the particles in an object. If the particles in a nebula have little kinetic energy, they move slowly and the temperature of the cloud is very low. If the particles move fast, the temperature is high. Section 1 A Solar System Is Born

12. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Chapter 20 The Solar Nebula, continued As the particles in a nebula move around, they sometimes crash into each other. Section 1 A Solar System Is Born When the particles move closer together, collisions cause the pressure to increase and particles are pushed apart.

13. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Chapter 20 The Solar Nebula, continued In a nebula, outward pressure balances the inward gravitation pull and keeps the cloud from collapsing. With pressure and gravity balanced, the nebula become stable. Section 1 A Solar System Is Born

14. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Chapter 20 Upsetting the Balance The balance between gravity and pressure in a nebula can be upset if two nebulas collide or if a nearby star explodes. These events compress, or push together, small regions of a nebula called globules, or gas clouds. Section 1 A Solar System Is Born

15. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Chapter 20 Upsetting the Balance, continued Globules can become so dense that they contract under their own gravity. As the matter in a globule collapses inward, the temperature increases and the stage is set for stars to form. The solar nebula—the cloud of gas and dust that formed our solar system—may have formed in this way. Section 1 A Solar System Is Born

16. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Chapter 20 How the Solar System Formed After the solar nebula began to collapse, it took about 10 million years for the solar system to form. Balance of gravity & pressure became unbalanced and the solar nebula collapsed inward The solar nebula became denser & and the gravitational attraction between gas and dust increased. The center of the cloud became very dense and hot. Section 1 A Solar System Is Born

17. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Chapter 20 How the Solar System Formed, continued Much of the gas and dust in the nebula began to rotate slowly around the center of the cloud. While the pressure at the center of the nebula was not enough to keep the cloud from collapsing, this rotation helped balance the pull of gravity. Over time, the solar nebula flattened into a rotating disk. All of the planets still follow this rotation. They collided to form planetesimals (which are small planets) Section 1 A Solar System Is Born

18. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Chapter 20 How the Solar System Formed, continued From Planetesimals to Planets As bits of dust circled the center of the solar nebula, some collided and stuck together to form golf ball-sized bodies. These bodies eventually drifted into the solar nebula, where further collisions caused them to grow. As more collisions happened, the bodies continued to grow. The largest of these bodies are called planetesimals, or small planets. Some of these planetesimals are part of the cores of current planets. Section 1 A Solar System Is Born

19. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Chapter 20 How the Solar System Formed, continued The central mass of the nebula became the sun, the planetesimals grew and eventually formed the planets Section 1 A Solar System Is Born

20. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Chapter 20 How the Solar System Formed, continued Closer to the center of the nebula, where Mercury, Venus, Earth, and Mars formed, temperatures were too hot for gases to remain. Therefore, the inner planets in our solar system are made of mostly rocky material. Section 1 A Solar System Is Born

21. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Chapter 20 How the Solar System Formed, continued Gas Giant or Rocky Planet? The largest planet- esimals formed near the outside of the rotating solar disk, where hydrogen and helium were located. These planetesimals were far enough from the solar disk that their gravity could attract the nebula gases. These outer planets grew to huge sizes and became the gas giants: Jupiter, Saturn, Uranus, and Neptune. Section 1 A Solar System Is Born

22. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Chapter 20 How the Solar System Formed, continued The Birth of a Star As the planets were forming, other matter in the solar nebula was traveling toward the center. The center became so dense and hot that hydrogen atoms began to fuse, or join, to form helium Fusion released huge amounts of energy and created enough outward pressure to balance the inward pull of gravity. When the gas stopped collapsing, our sun was born. Section 1 A Solar System Is Born

23. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Chapter 20 How the Solar System Formed, continued Smaller clumps of matter around the planetesimals became moons, asteroids, and comets Moons are satellites, which are bodies that revolve around larger bodies Section 1 A Solar System Is Born

24. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Chapter 20 Solar System Formation Section 1 A Solar System Is Born Click below to watch the Visual Concept. You may stop the video at any time by pressing the Esc key. Visual Concept

25. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Section 2 The Sun: Our Very Own Star Chapter 20 Bellringer Henry David Thoreau once said, “The sun is but a morning star.” What do you think this quotation means?

26. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Chapter 20 Describe the basic structure and composition of the sun. Explain how the sun generates energy. Describe the surface activity of the sun, and identify how this activity affects Earth. Objectives Section 2 The Sun: Our Very Own Star

27. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Chapter 20 The Structure of the Sun The sun is basically a large ball of gas made mostly of hydrogen and helium held together by gravity. 150 million km from Earth Medium sized & middle aged, yellow star Largest mass in our solar system Average star in terms of size, temp., and mass Supplies the energy for life on Earth Less dense than Earth because it is made of gases, while Earth is made of solids and liquids Section 2 The Sun: Our Very Own Star

28. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Chapter 20 The Structure of the Sun Although the sun may appear to have a solid surface, it does not. The visible surface of the sun starts at the point where the gas becomes so thick that you cannot see through it. The sun is made of several layers, as shown on the next slide. Section 2 The Sun: Our Very Own Star

29. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Chapter 20 Structure of the Sun Core – center of sun, H fuses to He and releases heat and light Radiative zone – 300,000 km thick Convective zone – gases circulate, 200,000 km thick Photosphere – innermost, surface of the sun Chromosphere – middle layer, thicker & hotter than photosphere Corona – Outermost layer, hotter than chromo & photo but not as hot as the core Section 2 The Sun: Our Very Own Star

30. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Chapter 20 Section 2 The Sun: Our Very Own Star

31. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Chapter 20 Energy Production in the Sun The sun has been shining on the Earth for about 4.6 billion years. Many scientists once thought that the sun burned fuel to generate its energy, but realized there was not enough energy to power sun The amount of energy that is released by burning would not be enough to power the sun. If the sun were simply burning, it would last for only 10,000 years. Section 2 The Sun: Our Very Own Star

32. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Chapter 20 Energy Production in the Sun, continued Burning of Shrinking? Scientists later began thinking that gravity was causing the sun to slowly shrink and that gravity would release enough energy to heat the sun. While the release of gravitational energy is more powerful than burning, it is not enough to power the sun. If all of the sun’s gravitational energy were released, the sun would last only 45 million years, and there are fossils that are older than that Section 2 The Sun: Our Very Own Star

33. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Chapter 20 Energy Production in the Sun, continued Nuclear Fusion Albert Einstein showed that matter and energy are interchangeable. Matter can change into energy according to his famous formula: E  mc 2 (E is energy, m is mass, and c is the speed of light.) Because c is such a large number, tiny amounts of matter can produce a huge amount of energy. Section 2 The Sun: Our Very Own Star

34. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Chapter 20 Energy Production in the Sun, continued The process by which two or more low-mass nuclei join together, or fuse, to form another nucleus is called nuclear fusion. In this way, four hydrogen nuclei can fuse to form a single nucleus of helium. During the process, energy is produced. Scientists now know that the sun gets its energy from nuclear fusion. Section 2 The Sun: Our Very Own Star

35. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Chapter 20 Energy Production in the Sun, continued Fusion in the Sun During fusion, under normal conditions, the nuclei of hydrogen atoms never get close enough to combine. The reason is that the nuclei are positively charged, and like charges repel each other, just as similar poles on a pair of magnets do. Section 2 The Sun: Our Very Own Star

36. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Chapter 20 Energy Production in the Sun, continued In the center of the sun, however, temperature and pressure are very high. As a result, hydrogen nuclei have enough energy to overcome the repulsive force, and hydrogen fuses into helium, as shown on the next slide. Section 2 The Sun: Our Very Own Star

37. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Chapter 20 Section 2 The Sun: Our Very Own Star

38. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Chapter 20 Energy Production in the Sun, continued Energy produced in the center, or core, of the sun takes millions of years to reach the sun’s surface. Energy passes from the core through a very dense region called the radiative zone. The matter in the radiative zone is so crowded that light and energy are blocked and sent in different directions. Section 2 The Sun: Our Very Own Star

39. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Chapter 20 Energy Production in the Sun, continued Eventually, energy reaches the convective zone. Gases circulate in the convective zone, which is about 200,000 km thick. Hot gases in the convective zone carry the energy up to the photosphere, the visible surface of the sun. From the photosphere, energy leaves the sun as light, which takes only 8.3 minutes to reach Earth. Section 2 The Sun: Our Very Own Star

40. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Chapter 20 Solar Activity, continued Sunspots The sun’s magnetic fields tend to slow down activity in the convective zone. When activity slows down, areas of the photosphere become cooler than the surrounding area. These cooler areas show up as sunspots. Sunspots are cooler, dark spots of the photosphere of the sun. Some sunspots can be as large as 50,000 miles in diameter. Change in cycles every 11 years. Believe sunspot activity causes lower temperatures on Earth Section 2 The Sun: Our Very Own Star

41. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Chapter 20 Solar Activity, continued Climate Confusion Sunspot activity can affect the Earth. Some scientists have linked the period of low sunspot activity, 1645-1715, with a period of very low temperatures that Europe experienced during that time, known as he “Little Ice Age.” Section 2 The Sun: Our Very Own Star

42. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Chapter 20 Solar Activity, continued Solar Flares The magnetic fields responsible for sunspots also cause solar flares. Solar flares are regions of extremely high temperatures and bright- ness that develop on the sun’s surface. When a solar flare erupts, it sends huge streams of electrically charged particles into the solar system. Solar flares can interrupt radio communications on the Earth and in orbit. Section 2 The Sun: Our Very Own Star

43. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Chapter 20 Solar Activity The churning of hot gases in the sun, combined with the sun’s rotation, creates magnetic fields that reach far out into space. The constant flow of magnetic fields from the sun is called the solar wind. Sometimes, solar wind interferes with the Earth’s magnetic field. This type of solar storm can disrupt TV signals and damage satellites. Section 2 The Sun: Our Very Own Star

44. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Bellringer The Earth is approximately 4.6 billion years old. The first fossil evidence of life on Earth has been dated between 3.7 billion and 3.4 billion year ago. Write a paragraph in your science journal describing what Earth might have been like during the first billion years of its existence. Chapter 20 Section 3 The Earth Takes Shape

45. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Chapter 20 Describe the formation of the solid Earth. Describe the structure of the Earth. Explain the development of Earth’s atmosphere and the influence of early life on the atmosphere. Describe how the Earth’s oceans and continents formed. Objectives Section 3 The Earth Takes Shape

46. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Chapter 20 The Earth is mostly made of rock. Nearly three-fourths of its surface is covered with water. Our planet is surrounded by a protective atmosphere of mostly nitrogen and oxygen, and smaller amounts of other gases. Formation of the Solid Earth Section 3 The Earth Takes Shape

47. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Chapter 20 The Earth formed as planetesimals in the solar system collided and combined. From what scientists can tell, the Earth formed within the first 10 million years of the collapse of the solar nebula. Formation of the Solid Earth, continued Section 3 The Earth Takes Shape

48. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Chapter 20 The Effects of Gravity When a young planet is still small, it can have an irregular shape. As the planet gains more matter, the force of gravity increases. When a rocky planet, such as Earth, reaches a diameter of about 350 km, the force of gravity becomes greater than the strength of the rock. As the Earth grew to this size, the rock at its center was crushed by gravity and the planet started to become round. Formation of the Solid Earth, continued Section 3 The Earth Takes Shape

49. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Chapter 20 The Effects of Heat As the Earth was changing shape, it was also heating up. As planetesimals continued to collide with the Earth, the energy of their motion heated the planet. Radioactive material, which was present in the Earth as it formed, also heated the young planet. Formation of the Solid Earth, continued Section 3 The Earth Takes Shape

50. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Chapter 20 After Earth reached a certain size, the temperature rose faster than the interior could cool, and the rocky material inside began to melt. Today, the Earth is still cooling from the energy that was generated when it formed. Volcanoes, earthquakes, and hot springs are effects of this energy trapped inside the Earth. Formation of the Solid Earth, continued Section 3 The Earth Takes Shape

51. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Chapter 20 As the Earth’s layers formed, denser materials, such as nickel and iron, sank to the center of the Earth and formed the core. Less dense materials floated to the surface and became the crust. This process is shown on the next slide. How the Earth’s Layers Formed Section 3 The Earth Takes Shape

52. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Chapter 20 Section 3 The Earth Takes Shape

53. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Chapter 20 The crust is the thin and solid outermost layer of the Earth above the mantle. It is 5 to 100 km thick. Crustal rock is made of materials that have low densities, such as oxygen, silicon, and aluminum. How the Earth’s Layers Formed, continued Section 3 The Earth Takes Shape

54. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Chapter 20 The mantle is the layer of rock between the Earth’s crust and core. It extends 2,900 km below the surface. Mantel rock is made of materials such as magnesium and iron. It is denser than crustal rock. How the Earth’s Layers Formed, continued Section 3 The Earth Takes Shape

55. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Chapter 20 The core is the central part of the Earth below the mantle. It contains the densest materials, including nickel and iron. The core extends to the center of the Earth—almost 6,400 km below the surface. How the Earth’s Layers Formed, continued Section 3 The Earth Takes Shape

56. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Chapter 20 Earth’s Early Atmosphere Scientists think that the Earth’s early atmosphere was a mixture of gases that were released as the Earth cooled. During the final stages of the Earth’s formation, its surface was very hot—even molten in places. The molten rock released large amounts of carbon dioxide and water vapor. Formation of the Earth’s Atmosphere Section 3 The Earth Takes Shape

57. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Chapter 20 Earth’s Changing Atmosphere As the Earth cooled and its layers formed, the atmosphere changed again. This atmosphere probably formed from volcanic gases. Volcanoes released chlorine, nitrogen, and sulfur, in addition to large amounts of carbon dioxide and water vapor. Some of this water vapor may have condensed to form the Earth’s first oceans. Formation of Earth’s Atmosphere, continued Section 3 The Earth Takes Shape

58. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Chapter 20 Comets, which are planetesimals made of ice, may have contributed to this change of Earth’s atmosphere. As they crashed into the Earth, comets brought in a range of elements, such as carbon, hydrogen, oxygen, and nitrogen. Comets also may have brought some of the water that helped form the oceans. Formation of Earth’s Atmosphere, continued Section 3 The Earth Takes Shape

59. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Chapter 20 Ultraviolet Radiation Scientists think that ultraviolet (UV) radiation helped produce the conditions necessary for life. UV light has a lot of energy and can break apart molecules. Earth’s early atmosphere probably did not have the protection of the ozone layer that now shields our planet from most of the sun’s UV rays. So many of the molecules in the air and at the surface were broken apart by UV radiation. The Role of Life Section 3 The Earth Takes Shape

60. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Chapter 20 Over time, broken down molecular material collected in the Earth’s waters, which offered protection from UV radiation. In these sheltered pools of water, chemicals may have combined to form the complex molecules that made life possible. The first life-forms were very simple and did not need oxygen to live. The Role of Life, continued Section 3 The Earth Takes Shape

61. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Chapter 20 The Source of Oxygen Sometime before 3.4 billion years ago, organisms that produced food by photo- synthesis appeared. Photosynthesis is the process of absorbing energy from the sun and carbon dioxide from the atmosphere to make food. During the process of making food, these organisms released oxygen—a gas that was not abundant in the atmosphere at the time. The Role of Life, continued Section 3 The Earth Takes Shape

62. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Chapter 20 Photosynthetic organisms played a major role in changing Earth’s atmosphere to become the mixture of gases it is today. Over the next hundreds of millions of years, more oxygen was added to the atmosphere while carbon dioxide was removed. The Role of Life, continued Section 3 The Earth Takes Shape

63. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Chapter 20 As oxygen levels increased, some of the oxygen formed a layer of ozone in the upper atmosphere. The ozone blocked most of the UV radiation and made it possible for life, in the form of simple plants, to move onto land about 2.2 billion years ago. The Role of Life, continued Section 3 The Earth Takes Shape

64. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Chapter 20 Scientists think that the oceans probably formed during Earth’s second atmosphere, when the Earth was cool enough for rain to fall and remain on the surface. After millions of years of rainfall, water began to cover the Earth. By 4 billion years ago, a global ocean covered the planet. Formation of Oceans and Continents Section 3 The Earth Takes Shape

65. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Chapter 20 Ocean Formation Section 3 The Earth Takes Shape Click below to watch the Visual Concept. You may stop the video at any time by pressing the Esc key. Visual Concept

66. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Chapter 20 The Growth of Continents After a while, some of the rocks were light enough to pile up on the surface. These rocks were the beginning of the earliest continents. The continents gradually thickened and slowly rose above the surface of the ocean. These continents did not stay in the same place, as the slow transfer of thermal energy in the mantle pushed them around. Oceans and Continents, continued Section 3 The Earth Takes Shape

67. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Chapter 20 About 2.5 billion years ago, continents really started to grow. By 1.5 billion years ago, the upper mantle had cooled and had become denser and heavier. At this time, it was easier for the cooler parts of the mantle to sink. These conditions made it easier for the continents to move in the same way they do today. Oceans and Continents, continued Section 3 The Earth Takes Shape

68. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Section 4 Planetary Motion Chapter 20 Bellringer A mnemonic device is a phrase, rhyme, or anything that helps you remember a fact. Create a mnemonic device that will help you differentiate between planetary rotation and revolution. Record your mnemonic device in your science journal.

69. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Chapter 20 Explain the difference between rotation and revolution. Describe three laws of planetary motion. Describe how distance and mass affect gravitational attraction. Objectives Section 4 Planetary Motion

70. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Chapter 20 Each planet spins on its axis. The spinning of a body, such a planet, on its axis is called rotation. The orbit is the path that a body follows as it travels around another body in space. A revolution is one complete trip along an orbit. A Revolution in Astronomy Section 4 Planetary Motion

71. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Chapter 20 Section 4 Planetary Motion Earth’s Rotation and Revolution

72. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Chapter 20 Johannes Kepler made careful observations of the planets that led to important discoveries about planetary motion. Kepler’s First Law of Motion Kepler discovered that the planets move around the sun in elliptical orbits. A Revolution in Astronomy, continued Section 4 Planetary Motion

73. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Chapter 20 Section 4 Planetary Motion Ellipse

74. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Chapter 20 Kepler’s Second Law of Motion Kepler noted that the planets seemed to move faster when they are close to the sun and slower when they are farther away. A Revolution in Astronomy, continued Section 4 Planetary Motion

75. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Chapter 20 Kepler’s Third Law of Motion Kepler observed that planets more distant from the sun, such as Saturn, take longer to orbit the sun. A Revolution in Astronomy, continued Section 4 Planetary Motion

76. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Chapter 20 Kepler did not understand what causes the plans farther from the sun to move slower than the closer planets. Sir Isaac Newton’s description of gravity provides an answer. Newton to the Rescue! Section 4 Planetary Motion

77. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Chapter 20 The Law of Universal Gravitation Newton’s law of universal gravitation states that the force of gravity depends on the product of the masses of the objects divided by the square of the distance between the objects. According to this law, if two objects are moved farther apart, there will be less gravitational attraction between them. Newton to the Rescue! continued Section 4 Planetary Motion

78. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Chapter 20 Orbits Falling Down and Around Inertia is an object’s resistance to change in speed or direction until an outside force acts on the object. Gravitational attraction keeps the planets in their orbits. Inertia keeps the planets moving along their orbits. Newton to the Rescue! continued Section 4 Planetary Motion

79. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Chapter 20 Section 4 Planetary Motion Gravity and the Motion of the Moon

80. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Formation of the Solar System Concept Map Use the terms below to complete the concept map on the next slide. Chapter 20 comets planets suns solar nebulas orbit solar systems nuclear fusion planetesimals

81. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Formation of the Solar System Chapter 20

82. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Formation of the Solar System Chapter 20

83. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu End of Chapter 20 Show

84. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Standardized Test Preparation Reading Read each of the passages. Then, answer the questions that follow each passage. Chapter 20

85. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Standardized Test Preparation Passage 1 You know that you should not look at the sun, right? But how can we learn anything about the sun if we can’t look at it? We can use a solar telescope! About 70 km southwest of Tucson, Arizona, is Kitt Peak National Observatory, where you will find three solar telescopes. In 1958, Kitt Peak was chosen from more than 150 mountain sites to be the site for a national observatory. Continued on the next slide Chapter 20

86. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Standardized Test Preparation Passage 1, continued Located in the Sonoran Desert, Kitt Peak is on land belonging to the Tohono O’odham Indian nation. On this site, the McMath-Pierce Facility houses the three largest solar telescopes in the world. Astronomers come from around the globe to use these telescopes. The largest of the three, the McMath-Pierce solar telescope, produces an image of the sun that is almost 1 m wide! Chapter 20

87. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Standardized Test Preparation 1. Which of the following is the largest telescope in the world? A Kitt Peak B Tohono O’odham C McMath-Pierce D Tucson Chapter 20

88. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Standardized Test Preparation 1. Which of the following is the largest telescope in the world? A Kitt Peak B Tohono O’odham C McMath-Pierce D Tucson Chapter 20

89. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Standardized Test Preparation 2. According to the passage, how can you learn about the sun? F You can look at it. G You can study it by using a solar telescope. H You can go to Kitt Peak National Observatory. I You can study to be an astronomer. Chapter 20

90. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Standardized Test Preparation 2. According to the passage, how can you learn about the sun? F You can look at it. G You can study it by using a solar telescope. H You can go to Kitt Peak National Observatory. I You can study to be an astronomer. Chapter 20

91. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Standardized Test Preparation 3. Which of the following is a fact in the passage? A One hundred fifty mountain sites contain solar telescopes. B Kitt Peak is the location of the smallest solar telescope in the world. C In 1958, Tucson, Arizona, was chosen for a national observatory. D Kitt Peak is the location of the largest solar telescope in the world. Chapter 20

92. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Standardized Test Preparation 3. Which of the following is a fact in the passage? A One hundred fifty mountain sites contain solar telescopes. B Kitt Peak is the location of the smallest solar telescope in the world. C In 1958, Tucson, Arizona, was chosen for a national observatory. D Kitt Peak is the location of the largest solar telescope in the world. Chapter 20

93. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Standardized Test Preparation Passage 2 Sunlight that has been focused can produce a great amount of thermal energy—enough to start a fire. Now, imagine focusing the sun’s rays by using a magnifying glass that is 1.6 m in diameter. The resulting heat could melt metal. If a conventional telescope were pointed directly at the sun, it would melt. To avoid a meltdown, the McMath-Pierce solar telescope uses a mirror that produces a large image of the sun. Continued on the next slide Chapter 20

94. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Standardized Test Preparation Passage 2, continued This mirror directs the sun’s rays down a diagonal shaft to another mirror, which is 50 m underground. This mirror is adjustable to focus the sunlight. The sunlight is then directed to a third mirror, which directs the light to an observing room and instrument shaft. Chapter 20

95. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Standardized Test Preparation 1. In this passage, what does the word conventional mean? A special B solar C unusual D ordinary Chapter 20

96. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Standardized Test Preparation 1. In this passage, what does the word conventional mean? A special B solar C unusual D ordinary Chapter 20

97. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Standardized Test Preparation 2. What can you infer from reading the passage? F Focused sunlight can avoid a meltdown. G Unfocused sunlight produces little energy. H A magnifying glass can focus sunlight to produce a great amount of thermal energy. I Mirrors increase the intensity of sunlight. Chapter 20

98. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Standardized Test Preparation 2. What can you infer from reading the passage? F Focused sunlight can avoid a meltdown. G Unfocused sunlight produces little energy. H A magnifying glass can focus sunlight to produce a great amount of thermal energy. I Mirrors increase the intensity of sunlight. Chapter 20

99. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Standardized Test Preparation 3. According to the passage, which of the following statements about solar telescopes is true? A Solar telescopes make it safe for scientists to observe the sun. B Solar telescopes don’t need to use mirrors. C Solar telescopes are built 50 m underground. D Solar telescopes are 1.6 m in diameter. Chapter 20

100. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Standardized Test Preparation 3. According to the passage, which of the following statements about solar telescopes is true? A Solar telescopes make it safe for scientists to observe the sun. B Solar telescopes don’t need to use mirrors. C Solar telescopes are built 50 m underground. D Solar telescopes are 1.6 m in diameter. Chapter 20

101. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Standardized Test Preparation Interpreting Graphics The diagram below models the moon’s orbit around the Earth. Use the diagram below to answer the questions that follow. Chapter 20

102. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Standardized Test Preparation 1. Which statement best describes the diagram? Chapter 20 A Orbits are straight lines. B The force of gravity does not affect orbits. C Orbits result from a combination of gravitational attraction and inertia. D The moon moves in three different directions depending on its speed.

103. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Standardized Test Preparation 1. Which statement best describes the diagram? Chapter 20 A Orbits are straight lines. B The force of gravity does not affect orbits. C Orbits result from a combination of gravitational attraction and inertia. D The moon moves in three different directions depending on its speed.

104. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Standardized Test Preparation 2. In which direction does gravity pull the moon? Chapter 20 F toward the Earth G around the Earth H away from the Earth I toward and away from the Earth

105. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Standardized Test Preparation 2. In which direction does gravity pull the moon? Chapter 20 F toward the Earth G around the Earth H away from the Earth I toward and away from the Earth

106. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Standardized Test Preparation 3. If the moon stopped moving, what would happen? Chapter 20 A It would fly off into space. B It would continue to orbit the Earth. C It would stay where it is in space. D It would move toward the Earth.

107. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Standardized Test Preparation 3. If the moon stopped moving, what would happen? Chapter 20 A It would fly off into space. B It would continue to orbit the Earth. C It would stay where it is in space. D It would move toward the Earth.

108. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Standardized Test Preparation Math Read each question, and choose the best answer. Chapter 20

109. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Standardized Test Preparation 1. An astronomer found 3 planetary systems in the nebula that she was studying. One system had 6 planets, another had 2 planets, and the third had 7 planets. What is the average number of planets in all 3 systems? A 3 B 5 C 8 D 16 Chapter 20

110. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Standardized Test Preparation 1. An astronomer found 3 planetary systems in the nebula that she was studying. One system had 6 planets, another had 2 planets, and the third had 7 planets. What is the average number of planets in all 3 systems? A 3 B 5 C 8 D 16 Chapter 20

111. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Standardized Test Preparation 2. A newly discovered planet has a period of rotation of 270 Earth years. How many Earth days are in 270 Earth years? F 3,240 G 8,100 H 9,855 I 98,550 Chapter 20

112. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Standardized Test Preparation 2. A newly discovered planet has a period of rotation of 270 Earth years. How many Earth days are in 270 Earth years? F 3,240 G 8,100 H 9,855 I 98,550 Chapter 20

113. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Standardized Test Preparation 3. A planet has seven rings. The first ring is 20,000 km from the center of the planet. Each ring is 50,000 km wide and 500 km apart. What is the total radius of the ring system from the planet’s center? A 353,000 km B 373,000 km C 373,500 km D 370,000 km Chapter 20

114. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Standardized Test Preparation 3. A planet has seven rings. The first ring is 20,000 km from the center of the planet. Each ring is 50,000 km wide and 500 km apart. What is the total radius of the ring system from the planet’s center? A 353,000 km B 373,000 km C 373,500 km D 370,000 km Chapter 20

115. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Standardized Test Preparation 4. If you bought a telescope for $87.75 and received a $10 bill, two $1 bills, and a quarter as change, how much money did you give the clerk? F $100 G $99 H $98 I $90 Chapter 20

116. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Standardized Test Preparation 4. If you bought a telescope for $87.75 and received a $10 bill, two $1 bills, and a quarter as change, how much money did you give the clerk? F $100 G $99 H $98 I $90 Chapter 20

117. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Chapter 20 Section 1 A Solar System Is Born

118. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Chapter 20 Section 1 A Solar System Is Born

119. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Chapter 20 Section 1 A Solar System Is Born

120. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Chapter 20 Section 2 The Sun: Our Very Own Star

121. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Chapter 20 Section 2 The Sun: Our Very Own Star

122. Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Standardized Test Preparation Chapter 20