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PLANET EARTH - CHAPTER 2 PRE-AP GEOGRAPHY AUGUST 22nd – 28th Holt McDougal, EARTH & THE SUN’S ENERGY All life on Earth requires solar energy, or energy from the sun, to survive. Earth’s rotation, revolution, tilt, and latitude all affect the amount of solar energy Earth receives. Secrets of the Sun Holt McDougal, EARTH & THE SUN’S ENERGY Rotation Earth spins on its axis— an imaginary line that runs through the center of the planet around which it turns. It takes Earth 24 hours to make one rotation, or complete spin on its axis. As Earth spins, different parts of the planet face the sun, thus causing the changes from day to night. Holt McDougal, Revolution Earth follows an orbit, or path, around the sun. Orbit is not a perfect circle. It takes Earth 365¼ days to complete one revolution, or trip around the sun. Our calendar year is based on the time it takes Earth to complete its orbit. EARTH & THE SUN’S ENERGY Tilt axis is tilted at an angle of 23½ degrees from vertical. Latitude Earth’s Latitude At Low-latitude Places High-latitude any give time of year, some places on Earth tilt toward the sun, and others tilt away. tilting toward the sun receive more solar energy and have warmer temperatures than those that tilt away. Holt McDougal, is the distance north or south of Earth’s equator. areas, those nearest the equator, receive direct rays from the sun all year. areas, those farther from the equator, receive indirect rays from the sun and have colder temperatures. EARTH & THE SUN’S ENERGY Seasons are periods during the year that are known for a particular type of weather. Many places experience four seasons—winter, spring, summer, and fall. In some parts of the world, seasons are based on the amount of rainfall Holt McDougal, EARTH & THE SUN’S ENERGY Winter and Summer • Earth tilts away from sun in winter and towards the sun in summer. • Because of the Earth’s tilt, the Northern and Southern hemispheres experience opposite seasons. Spring and Fall • In spring, Earth begins to tilt toward sun, solar energy increases, temperatures rise, and days grow longer. • In fall, the opposite occurs. Holt McDougal, Rainfall and Seasons • In the tropics, regions close to the equator, seasons are marked by rainfall rather than temperature. • At certain times of year, winds bring either dry or moist air to the tropics, creating wet and dry seasons. WATER ON EARTH • Water covers some two-thirds of the planet. Earth’s Water • About 97 percent of the Earth’s water • Unsafe to drink because of high levels of salt Salt Water • In general, found in Earth’s oceans, which cover some 71 percent of the planet’s surface • Also found in some of Earth’s lakes • Water without salt Freshwater • Makes up only 3 percent of our water supply Holt McDougal, WATER ON EARTH Much of Earth’s freshwater is locked in glaciers, large areas of slow moving ice, and in the ice of the Arctic and Antarctic regions. Surface water is water that is found in Earth’s streams, rivers, and lakes. Less than one percent of Earth’s water supply Streams, rivers, and lakes are common sources. Precipitation is water that falls to Earth’s surface as rain, snow, sleet, or hail. Streams form when precipitation collects in a narrow channel and flows toward the ocean. Most available freshwater is groundwater, water found below Earth’s surface. Some naturally bubbles from the ground to the surface as a spring. Most obtained by digging wells Holt McDougal, WATER ON EARTH Water is the only substance on Earth that occurs naturally as a solid, a liquid, and a gas, or water vapor. The water cycle is the movement of water from Earth’s surface to the atmosphere and back ; it is driven by the sun’s energy. Evaporation—water turns from liquid to gas. Condensation—the rising gas cools and condenses, or changes from a vapor into tiny liquid droplets, to form clouds. Precipitation—if the droplets in clouds become heavy enough, they fall back to Earth as rain, snow, sleet, or hail. Runoff—excess water that isn’t absorbed as groundwater flows over land and collects in streams, rivers, and oceans. Holt McDougal, WATER ON EARTH WATER CYCLE Holt McDougal, WATER ON EARTH Water Problems Lack of available freshwater, which can be caused by droughts or overuse Contaminated, or polluted, water can harm humans, plants, and animals. Flooding can damage property and threaten lives. Holt McDougal, Water Benefits Provides to eat us with food Important energy Provides source of us with recreation, including swimming, fishing, surfing, and sailing THE LAND Landforms, or shapes on the planet’s surface, make up the landscapes that surround us. Earth’s surface is covered with landforms of many different shapes and sizes. Mountains, land that rises higher than 2,000 feet Valleys, areas of low land located between mountains or hills Plains, stretches of mostly flat land Islands, water areas of land completely surrounded by Peninsulas, sides land surrounded by water on three Holt McDougal, THE LAND Earth’s Plates • The planet’s continents, or large landmasses, are part of Earth’s crust—the solid outer layer of the planet. • Theory of plate tectonics suggests that Earth’s surface is divided into a dozen or so slow-moving plates, or pieces of Earth’s crust. Movement of Continents • The idea that continents have traveled great distances over millions of years is known as continental drift. • Theory, developed by Alfred Wegener, states that the continents were once united in a single supercontinent and over time, slowly separated and moved to their present positions. • As plates collide, separate, and slide, they shape Earth’s landforms Holt McDougal, THE LAND Holt McDougal, THE LAND Plates Collide • Two ocean plates: one pushes under the other, creating ocean trenches, or deep valleys in ocean floor • Ocean and continental plate: ocean plate drops beneath continental plate, forcing land above to crumple and form mountain range • Two continental plates: land pushes up to form mountains Plates Separate • As plates move apart, gaps between plates allow magma to rise to Earth’s crust. • Lava, magma that reaches the Earth’s surface, emerges from the gap. • As lava cools, it builds a mid-ocean range, or underwater mountain, that can rise above the surface of the ocean to form islands. Holt McDougal, Plates Slide • As plates pass by each other, they sometimes grind together, producing earthquakes, sudden, violent movements of Earth’s crust. • Earthquakes often take place along faults, or breaks in Earth’s crust where movement occurs. • The region around the Pacific plate, called the Ring of Fire, is home to most of the world’s earthquakes and volcanoes. THE LAND I FEEL THE EARTH MOVE UNDER MY FEET Holt McDougal, THE LAND Weather, water, and other forces change Earth’s landforms by wearing them away or reshaping them. Weathering is the process by which rock is broken down into smaller pieces called sediment. Heating and cooling can cause rocks to crack. Expansion of water as it freezes can cause cracks to expand. Roots of trees can pry rocks apart. Erosion is the movement of sediment from one location to another. Can wear away or build up landforms Holt McDougal, THE LAND Wind Erosion • Winds lift sediment into air and carry it across great distances • On beaches and in deserts, deposits can form dunes. • Blowing sand can wear down rock. Glacial Erosion Water Erosion • Glaciers, or large, slow-moving sheets of ice, erode the land by carving valleys and mountain peaks. • Waves and flowing water can cut through rock, carry sediment, and deposit sediment in new locations. • Crush rock into sediment and move it great distances • Floodplains are created when rivers flood their banks and deposit sediment. Holt McDougal, THE LAND Landforms can influence where people settle. Landforms often influence what jobs are available in a region. Landforms can affect language. People sometimes change landforms to suit their needs. Holt McDougal,