Planet Earth http://youtu.be/vNaXxXNFOjM Chapter Two

The Earth and the Sun’s Energy All life on Earth requires solar energy, or energy from the sun, to survive Amount of solar energy received changes constantly Earth’s rotation, revolution, tilt, and latitude all affect the amount of solar energy Earth receives

Rotation Earth spins on its axis-an imaginary line that runs through the center of the planet around which it turns It takes 24 hours to make one rotation, or complete spin on its axis As earth spins, different parts of the planet face the sun, causing the changes from day to night

Revolution Earth follows an orbit or path around the sun Orbit is not a perfect circle It takes 365 ¼ days to complete one revolution, or trip around the sun Our calendar is based on the time it takes Earth to complete its orbit http://youtu.be/JaG70cJ8vDE Stop at 1:53

Tilt Earths axis is tilted at an angle of 23 ½ degrees from vertical At any given time on Earth, some places on Earth tilt toward the sun, and others tilt away Places tilting toward the sun receive more solar energy and have warmer temperatures than those that tilt away

Latitude Latitude is the distance north or south of the Earth’s equator Low-latitude areas, those nearest to the equator, receive direct rays from the sun all year High-latitude areas, those farther from the equator, receive indirect rays from the sun and have colder temperatures

Seasons Earth’s seasons are caused the planets tilt Many places experience four seasons Winter, spring, summer, fall In some parts of the world, seasons are based on the amount of rainfall

Seasons Winter and Summer Spring and Fall Earth tilts away from the sun in the winter and towards it in the summer Because of the Earth’s tilt, the Northern and Southern hemispheres experience opposite seasons In spring, Earth begins to tilt toward sun, solar energy increases, temperatures rise, and days grow longer In fall, the opposite occurs

Rainfall and the seasons In the tropics, regions close to the equator, seasons are marked by rainfall rather than temperature At certain times of the year, winds bring either dry or moist air to the tropics, creating wet and dry seasons

Water on Earth There are two types of water on Earth. What are they?

Earth’s Water Water covers 2/3 of the planet Salt Water About 97% of the Earth’s water Unsafe to drink because of high salt levels In general, found in the Earth’s oceans, which cover about 71% of the Earth’s surface Also found in some of Earth’s lakes

Freshwater Water without salt Makes up only 3% of the water supply Much freshwater locked in glaciers, large areas of slow moving ice, and in the ice of the Arctic and Antarctic regions Surface water is found in streams, rivers, and lakes Less than 1% of the Earth’s water supply

Freshwater Precipitation: water that falls to the Earth as rain, snow, sleet, or hail Streams form when precipitation collects in narrow channels and flows toward the ocean Most available freshwater is groundwater, water found below the Earth’s surface Some naturally bubbles from the ground to the surface as a spring Most obtained by digging wells

Water Cycle Water circulates from the Earth’s surface to the atmosphere and back again It is driven by the sun’s energy Water is the only substance on Earth that occurs naturally as a solid, a liquid, and a gas, or water vapor http://youtu.be/YswL4dIDQuk

Water Cycle Evaporation: water turns from liquid to gas Condensation: rising gas cools and condenses, or changes from a vapor into tiny liquid droplets, to form clouds Precipitation: if the droplets in the clouds become heavy enough, they fall back to the 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

The Role of Water in Our Lives Water Problems Water Benefits Lack of available freshwater Caused by droughts or overuse Contaminated, or polluted, water can harm humans, plants, and animals Flooding can damage property and threaten lives Provides us with food to eat Important source of energy Provides us with recreation, including, swimming, fishing, surfing, and sailing

Earth’s Landforms Landforms: shapes on the planet’s surface, make up the landscapes that surround us Mountains: land that rises higher than 2000 feet Valleys: areas of low land located between mountains or hills Plains: stretches of mostly flat land Islands: areas of land completely surrounded by water Peninsulas: land surrounded by water on three sides

Earth’s Plates The planet’s continents, or large landmasses, are part of the Earth’s crust: the solid outer layer of the planet Theory of plate tectonics: The Earth’s surface is divided into a dozen or so slow-moving plates, or pieces of the Earth’s crust

Movement of Continents Continental Drift: The idea that continents have traveled great distances over millions of years Theory, developed by Alfred Wegener, states that 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 the Earth’s landforms

Plate Movement Group activity, pages 37-38 Plates Collide Define the term. Be sure to describe the cause and effect. Provide a visual graphic. Be able to draw and explain. Provide examples Plates Collide Plates Separate Plates Slide

Forces on the Earth’s Surface Weather, water, and other forces change Earth’s landforms by wearing them away or reshaping them Weathering: Process by which rock is broken down into smaller pieces called sediment Heating and cooling can cause rock to crack Expansion as rocks freeze can cause cracks to expand Roots of trees can pry rocks apart Erosion: movement of sediment from one location to another Can wear away or build up landforms

Types of Erosion Wind Erosion lifts sediment into the air and can carry it great distances On beaches and in deserts, deposits can cause dunes Blowing sand can wear down rock

Glacial Erosion Glaciers, or large slow moving sheets of ice, erode the land, by carving valleys and mountain peaks Crush rock into sediment and move it great distances

Water Erosion Waves and flowing water can cut through rock, carry sediment, and deposit sediment in new locations Floodplains are created when rivers flood their banks and deposit sediment Sediment carried all the way to the sea creates a delta

Landforms Influence Life Where people settle What jobs are available Language People sometimes change landforms to suit their needs Examples