Unit 1.1 Earth’s Structure and the Tectonic Cycle Statement The mobility of the earth’s crust produces endogenic forces, which give rise to geological structures within it. Crustal structures are created, modified and destroyed as part of the tectonic cycle.

The Earth’s Structure Learning Objectives To understand the internal structure of the Earth. To understand the make up of the planet. Knowledge and understanding of key concepts

Earth’s Crust Composed of two main layers, Lithosphere Surface. Hard, rigid and solid. Asthenosphere : Semi- solid. Viscous material capable of flowing.

The Continental Crust or Sial Also called Sial due to the large amounts of silica and aluminium present Km Thick Lies on top of the Lithosphere.

The Oceanic Crust Made up of older, ancient rock like basalt. Referred to as Sima due to the presence of silica and magnesium. Covers a larger area of earth’s surface.

Plate Tectonics Learning Objectives Be able to describe the theory of plate tectonics. Understand how plates move Explain what happens at the margins of plates. Understand the position of Ireland in relation to plate boundaries.

The World’s Ocean Floor

Plate Tectonics Theory There are several major plates and several smaller ones. Plates move as passengers on the semi molten asthenosphere. As plates move they slide, diverge and collide. This movement gives rise to earthquakes, volcanic activity, sea floor spreading and the creation of ocean ridges.

How do the Plate’s Move ? Ans: Convection Currents ! Warm magma rises from the interior of the earth. As it rises it cools and falls again. This process is repeated and results in convection currents that travel in circular motions. Consequently the plates are moved causing continental drift.

Continental Drift The theory that the continents moved was first proposed by a German Mathematician Alfred Wegner in Wegner proposed that 200 Million years ago all the continents formed one supercontinent called Pangaea (Gk all the land)

Pangaea

Evidence for Continental Drift Continental Fit Fossil Records Matching rock records Matching Fossils Matching glacial deposits

Sea Floor Spreading The theory of sea floor spreading is that the oceanic crust is widened as new crust is created along plate margins. Evidence: Rocks at the centre of the ocean floors have proven to be younger than rock at the plate margins.

Plate Margins

Plate Boundary Types Locate on Map !

Convergent Boundaries Where Plates Collide. E.g. South American and Nazca Plate. Associated Landform- Fold Mountains –The Andes, Volcanic Activity. Rock is changed and destroyed along these destructive boundaries in subduction zones.

Divergent Plate Boundaries Plates Move apart New rock is formed. These are therefor constructive boundaries. E.g. The American plates and the African Plates Creating the Mid-Atlantic Ridge.

Conservative Boundaries Known as Transform boundaries. Plates slip or slide past each other. E.g San Andreas Fault line. North American and Pacific Plates. Major Earthquake Zone, Cascadia

Subduction Continental-Oceanic Oceanic –Oceanic Continental- Continental

Oceanic –Oceanic Eurasian – Pacific Plate. The older heavier plate is subducted underneath the younger, lighter plate. As the older plate descends it is heated by magma and friction and is recycled into the mantle. Island arcs, e.g Japan rise from the ocean floor as magma is released resulting in volcanic activity

Oceanic -Oceanic

Oceanic –Continental Convergence The heavier oceanic plate is forced into the lighter continental plate. The oceanic plate is subducted into the asthenosphere where it is melted back into the mantle. This melting releases upwelling magma resulting in Volcanic Activity. The lighter continental plate is buckled upward to create fold mountains. Nazca and South American Plates.

Oceanic – Continental Convergence

Continental-Continental When continental plates collide the lithosphere subducts. Both plate remain afloat but continue to push into each other. As a result a wide plateau of mountains is created. E.g. The Himalayas where the Indian and Eurasian Plates collide.

Continental-Continental

The formation of Ireland P 14 You Tube m/watch?v=BE5nLCOih 7I

Key Concepts Lithosphere Asthenosphere Endogenic Convection Currents Continental Drift Sea floor Spreading Conservative Boundary Divergent Boundary Transform Boundary Subduction Plateau Pangaea