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: Pressure 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 The Asthenosphere The lower mantle 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 The fluid density Fluid flow Changes Different Temperature The fluid density Fluid flow The force of gravity

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 older Younger older

Subduction Deep-ocean trenches

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

Where the plates move away from each other and crust is created. 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. Oceanic and continental 2. Oceanic and oceanic 3.Continental and continental

Transform boundary: Locations where two plates slip past each other, moving in opposite directions.

Faults