ch.2 planet earth

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Copyright © by Houghton Mifflin Harcourt Publishing Company

Chapter 2

World Geography

Earth and the Sun’s Energy

The Big Idea

Earth’s movement and the sun’s energy interact to create day and night, temperature changes, and the seasons.

Main Ideas• Earth’s movement affects the amount of energy we receive from the sun.• Earth’s seasons are caused by the planet’s tilt.


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Main Idea 1: Earth’s movement affects the amount of energy we receive from the sun.

• 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.


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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.

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.

Rotation and Revolution


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Latitude

• Latitude is the distance north or south of Earth’s equator.

•Low-latitude areas, those nearest 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.

Tilt

•Earth’s axis is tilted at an angle of 23½ degrees from vertical.

•At any give time of year, 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.

Tilt and Latitude


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Main Idea 2: Earth’s seasons are caused by the planet’s tilt.

• 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


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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.

The Seasons

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.


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World Geography

Water on Earth

The Big Idea

Water is a dominant feature on Earth’s surface and is essential for life.

Main Ideas• Salt water and freshwater make up Earth’s water supply.

• In the water cycle, water circulates from Earth’s surface to the atmosphere and back again.

• Water plays an important role in people’s lives.


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Main Idea 1: Salt water and freshwater make up Earth’s water supply.

Earth’s Water

•Water covers some two-thirds of the planet.

Salt Water

•About 97 percent of the Earth’s water

•Unsafe to drink because of high levels of salt

•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

Freshwater

•Water without salt

•Makes up only 3 percent of our water supply


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Freshwater• 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

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World Geography


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Main Idea 2: In the water cycle, water circulates from Earth’s surface to the atmosphere and back again.

• 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.

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World Geography

Water Cycle


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World Geography

The Land

The Big Idea

Processes below and on Earth’s surface shape the planet’s physical features.

Main Ideas• Earth’s surface is covered by many different landforms.• Forces below Earth’s surface build up our landforms.• Forces on the planet’s surface shape Earth’s landforms.• Landforms influence people’s lives and culture.


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Main Idea 1: Earth’s surface is covered by many different landforms.

• 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, areas of land completely surrounded by water

– Peninsulas, land surrounded by water on three sides


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World Geography

Main Idea 2: Forces below Earth’s surface build up our landforms. 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


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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 Collide, Separate, and Slide

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.

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.

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Himalayas Lo’ihi Volcano


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Main Idea 3: Forces on the planet’s surface shape Earth’s landforms.

• 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


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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 by a river all the way to the sea creates a delta.

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.

Types of Erosion

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 to form islands.


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Main Idea 4: Landforms influence people’s lives and culture.

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.

ch.2 planet earth

Education

earths seasons

surface water

earths freshwater

earths streams

movement of water

water cycle

earths waterunsafe

earths waterwater