EARTHEARTH

Third Rock FromThe Sun

Pt. IIVolcanoes, Earthquakes

And How Plates Move

HOW PLATES MOVEHOW PLATES MOVE There are There are mountainsmountains

on the surface of Earth. on the surface of Earth. Mountains are beneath Mountains are beneath the ocean water, too. the ocean water, too. There are There are trenchestrenches in in the oceans bottoms. the oceans bottoms. Trenches are deep, low Trenches are deep, low areas that are very long. areas that are very long. What makes mountains What makes mountains and trenches? and trenches? Scientists developed a Scientists developed a theorytheory that answers that answers this question.this question.

VOCABULARY• Trench- a deep, long, low area of land

that resembles a valley.• Evidence- The information and facts

you can use to describe something.• Theory- an explanation with evidence

to support it.• Plate tectonics- the way Earth’s

plates move.

THE THEORYTHE THEORY A theory is an idea that A theory is an idea that

explains how or why explains how or why something happens. A something happens. A theory must havetheory must have evidence to support it.to support it.

The theory of plate The theory of plate tectonics explains how tectonics explains how mountains and trenches mountains and trenches are made.are made.

It states that the plates It states that the plates on Earth do not stay in on Earth do not stay in one place. Heat in the one place. Heat in the mantle causes the mantle causes the plates to move.plates to move.

EVIDENCE FOR THE EVIDENCE FOR THE THEORYTHEORY

When two plates When two plates bump together, bump together, Earth’s surface Earth’s surface wrinkles. This wrinkles. This makes mountains. makes mountains. The Himalayan The Himalayan mountains north of mountains north of India are evidence India are evidence that two continental that two continental plates bumped plates bumped together.together.

EVIDENCE FOR THE EVIDENCE FOR THE THEORYTHEORY

Sometimes an ocean plate Sometimes an ocean plate bumps into a continental bumps into a continental plate. The ocean plate is plate. The ocean plate is pulled under the pulled under the continental plate. A continental plate. A trench forms when the trench forms when the ocean plate is pulled ocean plate is pulled down. The trench is down. The trench is evidence that one plate is evidence that one plate is going under another plate. going under another plate. Mountains may form on Mountains may form on the continental plate when the continental plate when this happens.this happens.

VOLCANOES AND VOLCANOES AND EARTHQUAKESEARTHQUAKES

Volcanoes and Volcanoes and earthquakes are earthquakes are caused by changes caused by changes inside Earth. inside Earth. Some places have Some places have a lot of a lot of earthquakes and earthquakes and volcanoes. These volcanoes. These places are on the places are on the edge of plates.edge of plates.

VOLCANOESVOLCANOES A volcano forms A volcano forms

above cracks in above cracks in Earth’s surface.Earth’s surface.

Heat below Earth’s Heat below Earth’s surface melts rock.surface melts rock.

MagmaMagma is melted is melted rock (molten rock) rock (molten rock) that is found deep that is found deep in Earth.in Earth.

VOLCANOESVOLCANOES Magma rises Magma rises

toward the surface.toward the surface. When magma spills When magma spills

onto the surface of onto the surface of Earth, it is called Earth, it is called lava.lava.

Lava cools as it Lava cools as it moves away from moves away from the volcano.the volcano.

Cooled lava turns Cooled lava turns into hard rock.into hard rock.

VOLCANIC ROCKVOLCANIC ROCK

EARTHQUAKESEARTHQUAKES An An earthquake earthquake is a is a

sudden release of sudden release of energy caused by energy caused by moving rock.moving rock.

Many earthquakes Many earthquakes happen where two happen where two plates scrape against plates scrape against each other.each other.

The movement makes The movement makes energy build up until energy build up until the rock breaks.the rock breaks.

A crack where rock A crack where rock breaks and moves is breaks and moves is called a called a faultfault..

EARTHQUAKESEARTHQUAKES The ground shakes in The ground shakes in

an earthquake. After an earthquake. After a big earthquake, the a big earthquake, the ground may shake for ground may shake for weeks.weeks.

Each shake, or Each shake, or tremor, gets a little tremor, gets a little weaker.weaker.

When rock along the When rock along the fault completely fault completely settles into its new settles into its new position, the shaking position, the shaking stops.stops.

SUMMARYSUMMARY

Earth has 3 layers. Earth has 3 layers. The heat inside The heat inside Earth makes rock Earth makes rock move. Moving rock move. Moving rock near Earth’s surface near Earth’s surface makes plates moves. makes plates moves. When plates move, When plates move, mountains, mountains, trenches, trenches, earthquakes, and earthquakes, and volcanoes can form.volcanoes can form.