Plate Tectonics- Plate Movement

Plate Tectonic Theory

It is believed that millions of years ago (200 million), all continents were joined to one land mass, Pangaea, which later split into Laurasia in the north and Gondwanaland to the south.

Alfred Wegener put forward a theory regards their movement in 1912 with his theory of Continental Drift. His theory was based on observations such as:

Biological:

• Some fossils (e.g. Mesosaurus) are found in both Africa and South America
• Fossils of a fern (Glossopteris) are found widely across the southern continents.

Geological: 

• Rock types and geological structures are similar on both sides of the Atlantic. The Appalachian Mountains (N.America) and the Caledonian Mountains (Scotland) both have the same sequence of igneous and sedimentary rocks. 
• Coal is found in UK but needs warm, wet, humid conditions to form.
• Late-Carboniferous glaciations evidence exists in India, South America and Antarctica

Observational:

• The shapes of countries appear to 'fit' one another, for example, S. America and Africa. Especially when you look at the continental shelf rather than the present coastline.

In the 1940's-1960's the theory was revised and Plate Tectonic theory emerged, based on the premise that the lithosphere is divided into plates, which are moved by convection currents coming from the earth's core.

Further Evidence

Mid-Atlantic Ridge & Sea Floor Spreading

Sea floor spreading; where new ocean crust is being continually created in zones in the middle of oceans, such as the Mid-Atlantic ridge which is moving the Eurasian plate and North American plate apart by 2.5cm/year or 25 km in a million years.

Mid-Atlantic Ridge - A submerged mountain range, which extends from the Arctic Ocean to beyond the southern tip of Africa. Seafloor spreading over the past 100 to 200 million years has caused the Atlantic Ocean to grow from a tiny inlet of water between the continents of Europe, Africa, and the Americas into the vast ocean that exists today. 

In 1947, a team of scientists led by Maurice Ewing confirmed the existence of a rise in the central Atlantic Ocean, and found that the floor of the seabed beneath the layer of sediments consisted of basalt, not the granite which is the main constituent of continents. They also found that the oceanic crust was much thinner than continental crust. The new data that had been collected on the ocean basins also showed particular characteristics regarding the bathymetry. One of the major outcomes of these data sets was that all along the globe, a system of mid-oceanic ridges was detected. An important conclusion was that along this system, new ocean floor was being created.

Palaeomagnetism

Palaeomagnetism is the examination of the polarity of the rocks that make up the ocean floor. Grains of magnetite -- behaving like little magnets -- can align themselves with the orientation of the Earth's magnetic field. This means each time the polarity switches it results in magnetic stripes in the sea floor, which is exactly mirrored either side of the mid Atlantic ridge.

Ocean Trenches

Ocean trenches are where large areas of ocean floor are pulled downwards and destroyed, the opposite to sea floor spreading.