Unit 3

WWK: Know the current theory of tectonic plates and how it came to be.

Plate Tectonic Theory

Current Plate Tectonic Theory states that the earths outer shell consists of individual plates which intersect in various ways and thereby produce earthquakes, volcanoes, mountains etc.

Continental Drift Theory

Plate Tectonic Theory is based originally on the Continental Drift Theory which states that the continents drifted across the ocean bed.

This theory was first proposed by Abraham Ortelius in 1596, and further expanded upon by Alfred Wegener in 1912.

Evolution of Theory

Alfred Wegener first used the term “continental drift” in 1912.

The theory was not accepted by many scientists early on, because it failed to explain how the continents moved.

Theories on how plates move

Today the thoughts on how the plates are set in motion can be divided into the following: mantle convection, gravity forces, and earth rotation related.

Mantle Convection

Mantle Convection states that large scale convection current are transmitted through the asthenosphere which moves the tectonic plates.

Plume Tectonics

This theory is a slight modification on the idea that mantle convection moves the tectonic plate.

Instead of mantle convection moving the plates this states that mantle plumes rising from the deeper mantle are the driving force behind the movement of the plates.

Gravity

Gravity in relation to the movement of the plates is thought as a secondary source compared to the different ideas of mantle dynamics.

Ridge Push: gravitational sliding of the plates away from large scale mantle domes.

Gravity

Slab pull is thought to be the greatest force acting on the plates. It proposes that the plates are being pulled into trenches in the mantle, but the North American Plate, African, Eurasian and Antarctic plates are moving, yet are not being pulled in trenches.

Earth rotation

The moon and the suns gravitational pull on the earths crust could move the plates.

The Coriolis Effect acting on plates as they move around the globe.

Possible slight movements of the crust due to wobbles of Earth.

Current view of movement

Today it is generally accepted all three forces: mantle convection or variants such as plume theory, gravitational forces and earth rotations are all acting on the tectonic plates, but now debate is centered around which force is the most dominant on a given plate at a given time.

Today the driving forces of tectonic movement are still being researched by scientists within the fields of geophysics and tectonophysics.

video

http://www.youtube.com/watch?v=OinfMLdornU

KS

Who first proposed the idea of continental drift?