CONTINENTAL DRIFT AND PLATE TECTONICS

The Onion Earth  For thousands of years it was a mystery why the continents seemed to move  It was only in the last 35 years that it became apparent why the earth seemed to be changing beneath our feet  The reason was that the earth wasn’t solid like humans once thought

The Onion Earth (cont)  The earth can be divided into 5 different layers  These layers are, in order from the centre to the outside: Inner Core, Outer Core, Lower Mantle, Upper Mantle, Crust  Special pictures, similar to X-rays are taken from high above the earth using satellites to help figure out information about these layers

The Onion Earth (cont)

The Core  The Inner Core is forced into a solid ball from the pressure of the layers above – iron and nickel  It is at a temperature of over 6000 o C  The Outer Core is composed of iron and nickel  The temperature is over 5500 o C and forces the iron and nickel to a liquid form

The Mantle  The Lower Mantle is partly melted and has the consistency of taffy – partially melted silicate rocks  The temperature is around 4000 o C  The Upper Mantle is also partly melted and like taffy, but flows a little better than taffy - together with the crust forms the lithosphere  Its temperature is around 1000 o C

The Crust  The crust is the layer that we walk on, is home to plants and animals and soil, and is the area that is mined for minerals and oil and gas  The crust is very thick in continents, but can get very thin in oceans – sometimes only 5km thick  Under continents it may be up to 60km thick  Temperature is an average of 5 o C

What is Continental Drift?  Continental drift is the idea that the continents (the plates that make up the Earth’s crust) are constantly moving over top of the mantle  Don’t be worried – most move about as fast as fingernails grow (1-4cm per year)  The ones you need to worry about are the ones that are trying to move, but don’t on a yearly basis – eventually they will move and cause great damage Think EARTHQUAKES – more later on!

Evidence For Continental Drift  Probably one of the most obvious pieces of evidence for continental drift is the fact that many of the continents appear as though they may have once fit together  One scientist who put a lot of thought into this idea of cont. drift was Alfred Wegener ( )

Pangaea

Biological Evidence  In Wegener’s research, he noticed that several fossils of similar plants and animals appeared on totally different continents  Ex. Mesosaurus lived in freshwater lakes and has been found in eastern S. America and in southern Africa  It couldn’t swim in salt water, so how could it get to two different continents?

Rock Evidence  Wegener continued his research and found that rocks on both sides of the Atlantic were very similar  Ex. The Appalachian Mtns in N.A. have the same kinds and ages of rocks as mountains in Britain and Norway  Ex. Fossil trilobites in the Himalayas of India used to once live in seas, so how could they possibly end up on the highest mountains of the planet?

Geological Evidence  Coal beds that once formed in tropical, swampy areas are now found in moderate to cold climates of N.A., Europe and Antarctica  More evidence was present in grooves under glaciers – the grooves indicated that the glaciers had moved from areas that were now too warm for glaciers – how could this be possible?

Wegener’s Pangaea  In his book, The Origin of Continents and Oceans, Wegener surmised that the continents had once be joined together in a large supercontinent called Pangaea.  He also said that as Pangaea broke apart it formed a northern continent called Laurasia and a southern continent called Gondwanaland  Unfortunately for Wegener, he could not explain the forces moving the continents and at the time, his theories were rejected  The poor man died in Greenland in 1930, still looking for evidence to support his theories

The Theory of Plate Tectonics  Evidence collected by advanced technology indicated that Earth’s crust was moving  The theory stated that the Earth’s crust is broken up into plates  Some of the plates are pushing together – these are called converging plates  Some of the plates are pulling apart – these are called diverging plates  Some plates slide past one another – transform plate boundary

The Theory of Plate Tectonics  In places where the plates are moving apart (diverging), new crust is being crated by volcanic activity  Most of these areas are in the middle of the ocean and are called mid-ocean ridges where seafloor spreading occurs

The Theory of Plate Tectonics  In places where plates collide (converging) and one is forced under the other, subduction zones form  Usually, thinner, newer oceanic plate is forced underneath the older, thicker continental plate

The Plates  The major plates are as follows:  Eurasian plate – Europe and Asia  North American plate – obvious!  African plate – seriously!  South American plate – okay, already!  Antarctic plate – oh my…  Indo-Australian plate – India and Australia  Pacific plate, Juan de Fuca plate, Scotia plate, Nazca plate, Philippine plate, Cocos plate, Arabian plate, Caribbean plate

The Tectonic Plates