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1. 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. Resources Bellringers Chapter Presentation Transparencies Standardized Test Prep Visual Concepts Image and Math Focus Bank

3. Chapter 20 Formation of the Solar System Table of Contents Section 1 A Solar System Is Born Section 2 The Sun: Our Very Own Star Section 3 The Earth Takes Shape Section 4 Planetary Motion

4. Chapter 20 Section 1 A Solar System Is Born 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.

5. Chapter 20 Section 1 A Solar System Is Born Review • Explain how smaller objects stay in orbit around larger objects. • The force of gravity between two objects is affected by what two things. • What were the two main gases in the early atmosphere? • How did we end up with so much oxygen in the atmosphere? • Why is UV light both dangerous to life and essential for life? • Why are planets round? • What event initiated the formation of the solar system?

6. Chapter 20 Section 1 A Solar System Is Born Objectives • Explain the relationship between gravity and pressure in a nebula. • Describe how the solar system formed.

7. Chapter 20 Section 1 A Solar System Is Born 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. • Anebulais a large cloud of gas and dust in interstellar space

8. Chapter 20 Section 1 A Solar System Is Born 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.

9. Chapter 20 Section 1 A Solar System Is Born 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. • Gravity causes the particles in a nebula to be attracted to each other.

10. Chapter 20 Section 1 A Solar System Is Born 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.

11. Chapter 20 Section 1 A Solar System Is Born The Solar Nebula, continued • As the particles in a nebula move around, they sometimes crash into each other. • When the particles move closer together, collisions cause the pressure to increase and particles are pushed apart.

12. Chapter 20 Section 1 A Solar System Is Born 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.

13. Chapter 20 Section 1 A Solar System Is Born 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.

14. Chapter 20 Section 1 A Solar System Is Born 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.

15. Chapter 20 Section 1 A Solar System Is Born How the Solar System Formed • After the solar nebula began to collapse, it took about 10 million years for the solar system to form. • As the nebula collapsed, it became denser and the attraction between the gas and dust particles increased. The center of the cloud became very dense and hot.

16. Chapter 20 Section 1 A Solar System Is Born 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.

17. Chapter 20 Section 1 A Solar System Is Born 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.

18. Chapter 20 Section 1 A Solar System Is Born 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.

19. Chapter 20 Section 1 A Solar System Is Born 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.

20. Chapter 20 Section 1 A Solar System Is Born 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.

21. Chapter 20 Section 1 A Solar System Is Born How the Solar System Formed, continued • The structure of a nebula and the process that led to the birth of the solar system are reviewed in the following Visual Concepts presentation.

22. Chapter 20 Section 1 A Solar System Is Born Solar System Formation Click below to watch the Visual Concept. You may stop the video at any time by pressing the Esc key. Visual Concept

23. Chapter 20 Section 2 The Sun: Our Very Own Star Bellringer Henry David Thoreau once said, “The sun is but a morningstar.” What do you think this quotation means?

24. Chapter 20 Section 2 The Sun: Our Very Own Star Objectives • Describe the basic structure and composition of the sun. • Explainhow the sun generates energy. • Describe the surface activity of the sun, and identify how this activity affects Earth.

25. Chapter 20 Section 2 The Sun: Our Very Own Star The Structure of the Sun • The sun is basically a large ball of gas made mostly of hydrogen and helium held together by gravity. • 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.

26. Chapter 20 Section 2 The Sun: Our Very Own Star

27. Chapter 20 Section 2 The Sun: Our Very Own Star 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. • 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.

28. Chapter 20 Section 2 The Sun: Our Very Own Star 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.

29. Chapter 20 Section 2 The Sun: Our Very Own Star 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  mc2 • (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.

30. Chapter 20 Section 2 The Sun: Our Very Own Star 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.

31. Chapter 20 Section 2 The Sun: Our Very Own Star 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.

32. Chapter 20 Section 2 The Sun: Our Very Own Star 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.

33. Chapter 20 Section 2 The Sun: Our Very Own Star

34. Chapter 20 Section 2 The Sun: Our Very Own Star 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.

35. Chapter 20 Section 2 The Sun: Our Very Own Star 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.

36. Chapter 20 Section 2 The Sun: Our Very Own Star 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.

37. Chapter 20 Section 2 The Sun: Our Very Own Star 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.

38. Chapter 20 Section 2 The Sun: Our Very Own Star Sunspots Click below to watch the Visual Concept. You may stop the video at any time by pressing the Esc key. Visual Concept

39. Chapter 20 Section 2 The Sun: Our Very Own Star 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.”

40. Chapter 20 Section 2 The Sun: Our Very Own Star 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.

41. Chapter 20 Section 3 The Earth Takes Shape 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 journaldescribing what Earth might have been like during the first billion years of its existence.

42. Chapter 20 Section 3 The Earth Takes Shape Objectives • Describethe 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.

43. Chapter 20 Section 3 The Earth Takes Shape Formation of the Solid Earth • 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.

44. Chapter 20 Section 3 The Earth Takes Shape Formation of the Solid Earth, continued • 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.

45. Chapter 20 Section 3 The Earth Takes Shape Formation of the Solid Earth, continued • 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.

46. Chapter 20 Section 3 The Earth Takes Shape Formation of the Solid Earth, continued • 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.

47. Chapter 20 Section 3 The Earth Takes Shape Formation of the Solid Earth, continued • 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.

48. Chapter 20 Section 3 The Earth Takes Shape How the Earth’s Layers Formed • 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.

49. Chapter 20 Section 3 The Earth Takes Shape

50. Chapter 20 Section 3 The Earth Takes Shape How the Earth’s Layers Formed, continued • 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.