Plate movement

Plate movement

Earth structure

The internal structure of the earth can be divided into 3 main layers.

The core at the centre of the earth is approximately the size of mars, and is the densest part of the earth. It is made of iron and nickel rich rocks, and is divided into 2 parts, inner and outer core.

Inner-solid, temperatures over 6000®c

Outer- semi-molten, around 6371km deep.

Surrounding the core is the mantle, a semi-molten mass of silicate, iron and magnesium rich rocks. Temperatures near the core reach 5,000®c. The high temperatures generate convection currents. The top layer of the mantle, closest to the surface is more rigid

The crust is the thinnest layer of the earth, with the coolest, least dense rocks. They are rich in SOAPS. Silicon, oxygen, aluminium, potassium and sodium. The crust is separated from the mantle by the Moho Discontinuity. Combined, the upper mantle and the crust are known as the lithosphere.The asthenosphere is the highly viscous, mechanically weak and ductile deforming region of the upper mantle of the Earth.

The theory of plate tectonics has retained this simple threefold division, but new research has suggested that the crust and upper mantle should be divided into the lithosphere and the asthenosphere. The lithosphere consists of the crust and the rigid upper section of the mantle and is approximately 80-90 km thick. It is divided into seven very large plates and a number of smaller ones. Plates are divided into 2 categories, oceanic and continental, depending on the type of material from which they are made. Below the lithosphere is the semi-molten asthenosphere, on which the plates float and move.

. There are 2 types of crust

-Oceanic crust is thinner, around 6-10km, but denser, and mainly basaltic.

-Continental crust is up to 70km thick and less dense, composed of an array of igneous, sedimentary and metamorphic rocks

Plate tectonics theory

Plate tectonics is the theory that the earths surface is divided into several sections that glide over the mantle. The movement of these plates can be the cause of volcanic and seismic activity.

Evidence- Continental drift and palaeomagnetism and sea floor spreading

A jigsaw like fit was noticed between South America and Africa as early as 1620 by a philosopher, Francis Bacon. Many people observed the apparent coastal similarities of some continents and their coastlines with others, but the first to observe the continental shelves was Wegner. He noticed an almost perfect fit between the shelves of Africa and South America. This coastal jigsaw became the basis for his theory of continental drift. Wegner gathered evidence from 3 further sources, the geology, biology and climatology of the 2 continents. The remains of Mesosauras (Permian reptile) have been found in South America and Africa, as have rocks of similar age and formation. There has been evidence of glaciation in Brazil, a now tropical climate, such as rock striations. Wegner published his theory, stating all continents were all once joined together…