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CONTINENTAL
DRIFT AND PLATE
TECTONICS
The Onion Earth
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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)
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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 Onion Earth (cont)
The Core
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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 6000oC
The Outer Core is composed of iron and nickel
The temperature is over 5500oC and forces the iron
and nickel to a liquid form
The Mantle
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The Lower Mantle is partly melted and has the
consistency of taffy – partially melted silicate rocks
The temperature is around 4000oC
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 1000oC
The Crust
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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 5oC
What is Continental Drift?
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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
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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 (1880-1930)
Pangaea
Biological Evidence
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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
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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
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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
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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
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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
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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
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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
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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