Preview Section 1 A Solar System Is Born

Preview Section 1 A Solar System Is Born
Formation of the Solar System Preview 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 Concept Mapping

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.

Objectives Explain the relationship between gravity and pressure in a nebula. Describe how the solar system formed.

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

The Solar Nebula, continued
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.

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.

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.

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.

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.

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.

Upsetting the Balance, continued
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.

How the Solar System Formed
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.

How the Solar System Formed, continued
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.

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.

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.

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.

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.

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.

Solar System Formation
Section 1 A Solar System Is Born Solar System Formation Click below to watch the Visual Concept. Visual Concept

Section 2 The Sun: Our Very Own Star
Bellringer Henry David Thoreau once said, “The sun is but a morning star.” In your science journal, explain what you think this quotation means.

Objectives Describe the basic structure and composition of the sun.
Section 2 The Sun: Our Very Own Star Objectives 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.

The Structure of the Sun
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.

Energy Production in the Sun
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.

Energy Production in the Sun, continued
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.

(E is energy, m is mass, and c is the speed of light.)
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.

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.

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.

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.

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.

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.

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.

Solar Activity, continued
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.

Sunspots Section 2 The Sun: Our Very Own Star
Click below to watch the Visual Concept. Visual Concept

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, , 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 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 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 journal describing what Earth might have been like during the first billion years of its existence.

Objectives Describe the formation of the solid Earth.
Section 3 The Earth Takes Shape Objectives 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.

Formation of the Solid Earth
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.

Formation of the Solid Earth, continued
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.

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.

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.

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.

How the Earth’s Layers Formed
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.

How the Earth’s Layers Formed, continued
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.

Section 3 The Earth Takes Shape How the Earth’s Layers Formed, continued 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.

Section 3 The Earth Takes Shape How the Earth’s Layers Formed, continued 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.

Formation of the Earth’s Atmosphere
Section 3 The Earth Takes Shape Formation of the Earth’s Atmosphere 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 Earth’s Atmosphere, continued
Section 3 The Earth Takes Shape Formation of Earth’s Atmosphere, continued 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 Formation of Earth’s Atmosphere, continued 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.

The Role of Life 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, continued
Section 3 The Earth Takes Shape The Role of Life, continued 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.

Section 3 The Earth Takes Shape The Role of Life, continued 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.

Section 3 The Earth Takes Shape The Role of Life, continued 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.

Section 3 The Earth Takes Shape The Role of Life, continued 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.

Formation of Oceans and Continents
Section 3 The Earth Takes Shape Formation of Oceans and Continents 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.

Ocean Formation Section 3 The Earth Takes Shape
Click below to watch the Visual Concept. Visual Concept

Oceans and Continents, continued
Section 3 The Earth Takes Shape Oceans and Continents, continued 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 Oceans and Continents, continued 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.

Section 4 Planetary Motion
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.

Objectives Explain the difference between rotation and revolution.
Section 4 Planetary Motion Objectives Explain the difference between rotation and revolution. Describe three laws of planetary motion. Describe how distance and mass affect gravitational attraction.

A Revolution in Astronomy
Section 4 Planetary Motion A Revolution in Astronomy 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.

Earth’s Rotation and Revolution

A Revolution in Astronomy, continued
Section 4 Planetary Motion A Revolution in Astronomy, continued 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.

Ellipse

Section 4 Planetary Motion A Revolution in Astronomy, continued 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.

Section 4 Planetary Motion A Revolution in Astronomy, continued Kepler’s Third Law of Motion Kepler observed that planets more distant from the sun, such as Saturn, take longer to orbit the sun.

Newton to the Rescue! 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! continued
Section 4 Planetary Motion Newton to the Rescue! continued 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 Newton to the Rescue! continued 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.

Gravity and the Motion of the Moon

Formation of the Solar System
Concept Mapping Use the terms below to complete the concept map on the next slide. comets orbit planets solar systems suns nuclear fusion solar nebulas planetesimals

Formation of the Solar System

Preview Section 1 A Solar System Is Born

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