The Structure of the Earth and Plate Tectonics

mini version

The Crust

•This is where we live!

•The Earth’s crust is made of:

Continental Crust

- thick (10-70km)- buoyant (less dense than oceanic crust) - mostly old

Oceanic Crust

- thin (~7 km)- dense (sinks under continental crust)- young

Plate Tectonics

• The Earth’s crust is divided into 12 major plates which are moved in various directions.

• This plate motion causes them to collide, pull apart, or scrape against each other.

• Each type of interaction causes a characteristic set of Earth structures or “tectonic” features.

• The word, tectonic, refers to the deformation of the crust as a consequence of plate interaction.

Alfred L. Wegener•Geologist Alfred Wegener Geologist Alfred Wegener noticed similar rocks & fossil noticed similar rocks & fossil remains were found on remains were found on continents which seemed to continents which seemed to fit togetherfit together

•He called this “super” He called this “super” continent called Pangaea continent called Pangaea

• In 1912 Wegener In 1912 Wegener published the published the first version & first version & died defending died defending his theoryhis theory

PANGAEA - the large landmass that included all of Earth’s present day continents

Support for Continental Drift1. SHAPE OF THE CONTINENTS

Continents fit together like puzzle pieces

Mesosaurus was incapable of swimming across a large ocean.

2. FOSSIL EVIDENCE2. FOSSIL EVIDENCE

SAME FOSSILS: DIFFERENT CONTINENTS

Support for Continental Drift

3. ROCK EVIDENCE – Mountain ranges3. ROCK EVIDENCE – Mountain rangesSupport for Continental Drift

SAME ROCK: DIFFERENT RANGE Existing mountain ranges separated by vast oceans contain rocks of identical mineral content.

A prime example are the Appalachian Mountains in the eastern U.S and the Caledonian Mountains in the British Isles.

SAME ROCK: DIFFERENT RANGE Existing mountain ranges separated by vast oceans contain rocks of identical mineral content.

A prime example are the Appalachian Mountains in the eastern U.S and the Caledonian Mountains in the British Isles.

SAME SCARS: DIFFERENT CONTINENTS

Support for Continental DriftSupport for Continental Drift4. GLACIAL SCARS4. GLACIAL SCARS

5. LOCATION OF COAL DEPOSITS

Coal deposits have been found in temperate and polar regions; however, coal is formed in tropical regions.

Support for Continental DriftSupport for Continental Drift

Plate Movement•“Plates” of lithosphere are moved around by the underlying hot mantle convection cells

• Divergent

• Convergent

• Transform

Three types of plate boundary

• Iceland has a divergent plate boundary running through its middle

Iceland: An example of continental rifting

•There are three styles of convergent plate boundaries•Continent-continent collision•Continent-oceanic crust collision

•Ocean-ocean collision

Convergent Boundaries

• Forms mountains, e.g. European Alps, Himalayas

Continent-Continent Collision

•Called SUBDUCTION

Continent-Oceanic Crust Collision

•When two oceanic plates collide, one runs over the other which causes it to sink into the mantle forming a subduction zone.

•The subducting plate is bent downward to form a very deep depression in the ocean floor called a trench.

•The worlds deepest parts of the ocean are found along trenches. •E.g. The Mariana Trench is 11 km deep!

Ocean-Ocean Plate Collision

•Where plates slide past each otherTransform Boundaries

Above: View of the San Andreas transform fault

Volcanism is mostly focused at plate margins

Pacific Ring of Fire

•Hot mantle plumes breaching the surface in the middle of a tectonic plate

What are Hotspot Volcanoes?

Photo: Tom Pfeiffer / www.volcanodiscovery.com

The Hawaiian island chain are examples of hotspot volcanoes.

Where do earthquakes form?

Figure showing the tectonic setting of earthquakes

What is an earthquake?•They are caused by the release of energy

•They cause the ground to shake•Reasons:

•Plates Moving•Faults (cracks in Earth’s surface)•Caverns collapsing•Meteor Impacts•Volcanic Eruptions

The San Andreas is a •Strike Slip (Transform) Fault•One piece of Earth slides past another

Terms used to describe an earthquake

Focus vs. Epicenter

Focus: area beneath Earth’s surface where rock that was under stress begins to move or break.

Epicenter: Point on surface directly above the focus.

How are earthquakes detected?

•Earthquakes are detected by seismographs

•Seismographs record the information on a seismogram

How is the strength of the earthquake determined?

•Intensity•The effect of the Earthquake on the area•Measured by the Mercalli Scale (shaking)

•Magnitude•The actual energy released by the Earthquake•Measured by the Richter Scale (I-XII)