TOPIC 5: PLATE TECTONICS

YEAR 7

What’s inside earth ??

Pompeii

1. EARTH’S INTERIOR Earth’s surface is constantly changing Geologists have used two main types of

evidence to learn about Earth’s interior: Direct evidence from rock samples Indirect evidence from seismic waves

The three main layers of Earth are the crust, the mantle and the core.

They vary greatly in size, composition, temperature and pressure.

Temperature: Every 40m that you descend, the temperature rises

1 Celsius degree. The high temperatures inside the Earth are the

result of heat left over from the formation of the planet and radioactive substances releasing energy.

Pressure Because of the weight of the rock above, pressure

increases as we go deeper.

The Crust Layer of solid rock that includes both dry land

and the ocean floor. It is thickest under high mountains and

thinnest beneath the ocean. Oceanic crust (beneath the oceans) consists

mostly of rocks such as Basalt Continental crust (forms the continents)

consists mainly of rocks as Granite

BASALT

GRANITE

The Mantle About 40 km beneath the surface, you

find the solid part of the mantle. It is made up of rock that is very hot, but

solid. Scientist divide the mantle into layers

based on the physical characteristics of those layers.

It is nearly 3000 km thick.

The lithosphere Uppermost part of the mantle (similar to the crust) Crust and uppermost part of the mantle form a

rigid layer, called the lithosphere. The Asthenosphere

Below the lithosphere This part of the mantle is less rigid and somewhat

soft (it can bend like plastic) The lower mantle

Beneath the astenosphere and it is solid.

The Core

It is made mostly of the metals iron and nickel. It consists of two parts, a liquid outer core and

a solid inner core. It has a thickness of 3486 km

Earth’s magnetic field The movement in the liquid outer core create

Earth’s magnetic field.

2. CONVECTION AND THE MANTLE

Heat always move from a warmer substance to a cooler one.

There are three types of heat transfer: Radiation

Transfer of energy through space (I.e.: sunlight, flame…) Conduction

Heat transfer within a material or between materials that are touching (I.e.: spoon in a hot pot)

Convection Heat transfer by the movement of currents within a fluid.

(liquid and gas)

Convection Currents

Different Temperature

ChangesThe fluid density

The force of gravity

Fluid flow

Convection currents in Earth

Heat from the core and the mantle itself causes convection currents in the mantle and outer core.

3. DRIFTING CONTINENTS

Drifting Continents In 1912 ,a German Scientist called

Alfred Wegener all the continents were once stuck together as one big land mass called Pangaea.

The idea that continents can drift about is called, not surprisingly, continental drift.

Wegener gathered evidence to support continental drift:

Land features: Africa and South America matched up

Fossils: Fossil is any trace of an ancient organism that has been preserved in rock.

Climate: Climate changed when continent moved. He could not provide a satisfactory

explanation for the force that pushes or pulls the continents, that’s why his hypothesis was rejected.

4. SEA FLOOR SPREADING Scientists needed a clue as to how the

continents drifted. The discovery of the chain of mountains that lie under the oceans was the clue that they were waiting for.

In the mid-1900s, scientist mapped the mid ocean ridge using sonar (device that bounces sound waves off underwater objects and then records the echoes of these sound waves. The time it takes for the echo to arrive indicates the distance to the object)

Mid-Ocean Ridges An mountain chain beneath Earth’s oceans.

Sonar helps scientists mapped the mid-ocean ridges.

Sea-Floor Spreading It proposed by Harry Hess. In sea-floor spreading, the sea floor spreads

apart along both sides of a mid-ocean ridge as new crust is added. As a result, the ocean floors move like conveyor belts, carrying the continents along with them.

Evidence supported: molten material, magnetic stripes drilling samples.

Mid-ocean ridge

Mid-Ocean Ridge Basalts

Magnetic Pole have reversed

The scientist determined the age of the rocks in the samples from sea floor

Younger

older older

Deep-ocean trenches

Subduction

The ocean floor does not just keep spreading, it also plunges into deep underwater canyons called deep-ocean trenches.

The process by which ocean floor sinks beneath a deep-ocean trench and back into the mantle is called subduction.

5. The Theory of Plate Tectonics A scientific theory is a well-tested

concept that explains a wide range of observation.

Plates: The lithosphere is broken into separate sections.

The theory of plate tectonics explains the formation, movement, and subduction of Earth’s plates.

Plate Boundaries Faults : fauls breaks in Earth’s crust where

rocks have slipped past each other Faults form along plate boundaries. There are 3 types of boundaries:

Divergent boundaries Convergent boundaries Transform boundaries

Divergent boundary: Where the plates move away from each

other and crust is created.

A deep valley called a rift valley forms along the divergent boundary.

1. 2.

3. 4.

East African Rift Valley

Convergent boundary: the plates move towards each other and crust are destroyed.

3.Continental and continental

1. Oceanic and continental

2. Oceanic and oceanic

Transform boundary: Locations where two plates slip past each

other, moving in opposite directions.

Faults