The Earth’s Interior & Plate Tectonics

Physical Science Chapter 17 Section 1

The Earth’s InteriorThe Earth’s Interior can be broken up into 4 major zones

CrustMantleOuter coreInner core

Surrounding the interior

is theAtmosphere

The CrustThe crust is very thin (average 20 km) & Broken-up into plates.This does not sound very thin but if you were to imagine the Earth as a football, the crust would be about ½millimeter thick. The thinnest parts are under the oceans (Oceanic Crust) and go to a depth of roughly 10 kilometers. It is more dense than under continents.The thickest parts are the continents (Continental Crust) which extend down to 35 kilometers on average. The continental crust in the Himalayas is some 75 kilometres deep.

The MantleA rocky layer located below the crust with a thickness of 2885 kilometersThe upper part of the mantle together with the crust is called the Lithosphere.

The Mantle (cont…)The mantle extends about half way to the centre. It's made of solid rock and behaves like an extremely viscous liquid - (This is the tricky bit... the mantle is a solid which flows) The convection of heat from the centre of the Earth is what ultimately drives the movement of the tectonic plates and cause mountains to rise.

The Outer CoreA layer about 2270 kilometers thick, which is made of molten (liquid) iron & nickel.The movement of this liquid core is responsible for the Earth's magnetic field

The Inner CoreThe bit in the middle!It is made of solid iron and nickel with a radius of about 1216 km.Temperatures in the core are thought to be in the region of 5000-6000°c and it's solid due to the massive pressure.

The Theory of Plate Tectonics

States that Earth's rigid outer shell, called the lithosphere, consists of seven large and numerous smaller segments called plates that are in motion relative to each other.

Origins Alfred Wegner proposed Continental Drift when he noticed that the continents fit together like jigsaw pieces.Later, with more evidence, this became the theory of Plate Tectonics

Evidence for Plate TectonicsThe evidence Wegner used for his original theory

Continents fit togetherMatching Rocks & Fossils

Paleomagnetism: Study of the changes in Earth’s Magnetic Field

Evidence for the theory (cont…)The edges of these plates (called Plate Boundaries), where they move against each other, are sites of intense geologic activity, such as earthquakes, volcanoes, and mountain building.

Types of Plate Boundaries A. Divergent plate

boundaries

B. Convergent plate boundaries

C. Transform fault boundaries

Divergent Plate Boundaries(constructive margins)

Two plates move apart Mantle material upwells to create new seafloor Continental rifts form at spreading centers within a continent

Divergent Plate Boundaries (cont…)

Convergent plate boundaries (destructive margins)

Plates collide, an ocean trench forms and lithosphere is subducted into the mantle There are three types of Convergent Plate Boundary

Oceanic-continental convergence Denser oceanic slab sinks into the asthenospherePockets of magma develop and riseContinental volcanic arcs form

e.g., Andes Mountain Rangee.g., Cascades Mountain Range

Oceanic-oceanic convergence Two oceanic slabs converge and one descends beneath the otherOften forms volcanoes on the ocean floorVolcanic island arcs forms as volcanoes emerge from the sea

e.g., Aleutian islandse.g., Mariana islands

Continental-continental convergence When subducting plates contain continental material, two continents collideCan produce new mountain ranges such as the Himalayas

Example of a continental-continental Subduction

Transform Fault boundariesPlates slide past one another

No new crust is createdNo crust is destroyed