Land, Air, and Water

Chapter 2, Section 2

Forces Inside the Earth

• About 90% of the world’s earthquakes and many of the world’s active volcanoes occur in the Ring of Fire which circles the Pacific Ocean– Earthquakes and volcanoes are two

forces that shape and reshape the Earth.– Provide clues about the Earth’s structure

What is the Earth Made of?

• Water covers 75% of Earth’s surface in lakes, rivers, seas, and oceans– Only 25% of Earth’s surface is land

• Continents are unique because of their landforms, or shapes and types of land–Mountains are landforms that rise usually

more than 2,000 feet above sea level.–Wide at the bottom and rise steeply to a

narrow peak

What is the Earth Made of?

– Hills are lower and less steep than mountains, with rounded tops

– A plateau is a large, mostly flat area that rises above the surrounding land

– Plains are large areas of flat or gently rolling land

Pangaea: The Supercontinent

• Geographers theorize that millions of years ago the Earth had only one huge landmass. They called it Pangaea.

• Scientists reasoned that 200 million years ago, a force made Pangaea split into several pieces and it began to move apart. Separate pieces formed continents.

Pangaea: The Supercontinent

• Geographers explained the separation of the continents with plate tectonics– The outer skin of the Earth, called the

crust, broke into huge pieces called plates– Continents and oceans = top of crust–Magma, layer of hot rock = below plates– Plates float on the magma

• Continents are part of plates that shift over time

Volcanoes, Earthquakes, and Shifting Plates

• Plates move in different directions– Plates move apart and magma leaks out

through cracks in the crust• In the oceans the cooling rock forms

underwater mountains (ridges)

– Plates push against each other forcing one plate under another• Volcano is produced when pressure and heat

build up

Volcanoes, Earthquakes, and Shifting Plates

• Weak places along plate boundaries– Crust cracks and splinters from the

pressure (faults)

• Earthquake crust moves along fault lines and releases great amounts of energy

Forces on the Earth’s Surface

• Forces either build up the Earth or break it down–Weathering process that breaks rocks

down into tiny pieces• Wind, rain, ice• Helps create soil

– Erosion small pieces of rock carried to new places

Air and Water: Two Ingredients for Life

• Atmosphere a thick layer of gases that surrounds the Earth– Provides oxygen for people and animals– Provides carbon dioxide for plants– Holds in heat from the sun

Air and Water: Two Ingredients for Life

• About 97% of the Earth’s water is found in oceans

• Fresh water makes up a small %–Most is frozen in the North and South

poles– Lakes, rivers, rain, groundwater