Planet Earth Chapter 2
Earth and the Sun’s Energy Section 1
Earth’s Movements • All life on Earth requires solar energy • Amount of solar energy is constantly changing because of the Earth’s rotation, revolution, and tilt. • Rotation • Earth’s axis is an imaginary rod that runs from the north pole to the south pole • As it spins a different part of the planet faces the sun • It takes 24 hours to complete this rotation • The sun remains stationary as the Earth turns.
Revolution • As the Earth spins on its axis it also follows an orbit around the sun. • The orbit is an ellipse – sometimes Earth is closer to the sun and sometimes it is farther. • It takes 365 ¼ days for Earth to complete one revolution. • February 29 is added to the calendar every 4 years • Tilt and Latitude • Earth is tilted on its axis 23 ½ degrees. • At any given time of the year, some locations are tilted towards the sun and others are tilted away • This creates winter and summer • Places in a lower latitude, or close to the equator, receive direct rays from the sun all year long
The Seasons • Winter and Summer • Change in seasons is created by Earth’s tilt. • Winter occurs on parts of Earth that are tilted away from the sun get less direct solar energy, cool temperatures, and less daylight • Vice versa for summer. • Because of Earth’s tilt, the Northern and Southern hemispheres experience opposite seasons.
Spring and Fall • As Earth orbits the sun, there are periods when the poles tilt neither towards or away from the sun. • These periods mark spring and fall. • Rainfall and Seasons • Some regions have seasons marked by rainfall instead of temperatures. • The tropics experience these seasons. • Winds bring dry or moist air into the region and create wet and dry seasons.
Water on Earth Section 2
Earth’s Water Supply • Water covers two-thirds of the Earth • 97% is salt water – unsafe to drink • Most salt water is found in the oceans • Some lakes also contain salt water • Great Salt Lake, UT • Freshwater makes up only 3% of the Earth’s water supply. • Much of the freshwater is in Earth’s glaciers, and in the ice in the Arctic and Antarctic • The water we use everyday is found in lakes, rivers, and under the Earth’s surface.
Surface water is in streams, rivers, and lakes. • Less than 1% of our water supply comes from surface water. • Streams form from precipitation and join together to form rivers. • Some lakes are formed as rivers fill low-lying areas • Others are formed by glaciers carving deep holes in the Earth’s surface • Ex: Great Lakes • Most of our available freshwater is groundwater. • Groundwater is typically obtained by drilling into the ground.
The Water Cycle • Water occurs as a solid, a liquid, and a gas. • Water vapor is the invisible gas in the air. • Water is always moving on Earth. • The water cycle is this movement • The Sun’s energy drives the water cycle. • Because the cycle is constantly repeating, the supply of water on Earth remains fairly constant.
The cycle • Sun heats water on the Earth’s surface • Water turns into water vapor • Vapor rises into the air and cools • Vapor changes into droplets and these droplets join together to form clouds. • If the droplet becomes heavy enough, precipitation occurs. • The precipitation falls to Earth’s surface and is absorbed into groundwater or runs off into bodies of water.
Water and People • Water is crucial for survival • Many places on Earth face water shortages • Lack of fresh water • Droughts • Overuse • Polluted water • Flooding is another water problem • Flooding can cause property damage and threatens lives • Water also provides food, power, and recreation
The Land Section 3
Landforms • Landforms are shapes on the planet’s surface that make up the landscapes that surround us. • Mountains – rises higher than 2000 ft • 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
Forces below Earth’s Surface • The planet is made up of three layers. • Solid inner core, liquid mantle, solid crust • Continents are part of the Earth’s crust. • Plate tectonics suggests that Earth’s surface is divided into a dozen slow-moving plates • Use this to explain our landforms • Energy deep inside the Earth puts pressure on Earth’s crust and forces the plates to shift. • Plates move in different directions and at different speeds.
Movement of Continents • Plates move slowly – up to several inches per year • Over 200 million years we see that continents have moved a long distance • Alfred Wegener developed the theory of continental drift • Earth’s plates shifted over million of years • Plates are still moving today • They collide, separate, or slide past one another • These movements have shaped our landforms
Plates Collide • Collision of plates create ocean trenches and mountains • When 2 ocean plates collide, one plate pushes under the other. • This creates an ocean trench, or deep valley in the ocean floor • The deepest ocean trench is near Japan and the pacific plate moves under other plates – Mariana Trench • When an ocean plate and a continental plate collide the ocean plate drops beneath the continental plate. • Causes a mountain range • The Andes in South America formed when the South American plate and the Nazca plate collided.
When 2 continental plates collide large mountains are formed. • The Himalayas were formed when the Indian plate crashed into the Eurasian plate. • The Himalayas continue to grow as the two plates keep crashing into one another.
Plates Separate • As plates move apart, gaps between the plates allow magma to rise to the crust. • Lava emerges from the gap and as it cools it builds a mid-ocean ridge, or underwater mountain. • Separation of the North American and Eurasian plats formed the Mid-Atlantic Ridge. • If the mountains rise high enough they form volcanic islands - Iceland
Plates Slide • Tectonic plates can slide past one another. • This sliding causes earthquakes. • Earthquakes usually take place along faults. • The San Andreas Fault zone in California is a place where earthquakes are quite common. • North American plate and Pacific plate • The pacific plate is known as the Ring of Fire because it is home to most of the world’s earthquakes and volcanoes.
Forces on Earth’s Surface • Weathering • Rock is broken down into smaller pieces • Heat and water can cause rocks to crack or wash away • The small pieces of rock are known as sediment • Wind, ice, and water often move sediment
Erosion • Movement of sediment from one location to another • Can wear away or build up landforms • Powerful winds often cause erosion • Glaciers can cause massive erosion by melting and carving out a path for the water • Water is the most common cause of erosion • Waves can wear away at the coastline • Flowing water carves out new paths • The Grand Canyon
Landforms influence Life • Earth’s landforms affect our settlement and cultures • In early times people settled near deltas for easy transportation and fertile soil • Earliest settlement between the Tigris and Euphrates • Some landforms also discourage settlements • People also change landforms to suit their needs.