Download Plate Tectonics

L.O.1: To know the structure of the earth.
L.O.2: To understand the theories of
continental drift and plate tectonics.
Imagine the Earth as a hardboiled egg…………………….
The thin brittle shell is the crust that humans live on.
The thick jelly like white is the deep hot magma beneath
the surface.
The yellow yolk is the core of the earth.
PLATE TECTONICS is the study of the structure of the Earth, and how the
Earth's surface changes according to the movement of tectonic plates. Plate
tectonics is responsible for the formation of the most spectacular natural
features on Earth, such as mountain belts, volcanoes, rift valleys, hot springs and
mid-ocean ridges and also for the dramatic impacts of earthquakes.
THE STRUCTURE OF
THE EARTH
To understand how plate
tectonics work, first
you must have an idea of
the internal structure
of the Earth.
As you can see, the
Earth is composed of
several different layers,
the crust, mantle, inner
core and outer core.
They are slightly
different from each
other in terms of
thickness, temperature
and density.
CONVECTION
CURRENTS
The very hot core of the
earth acts just like a hot
plate or gas ring of a
cooker. As the rock at
the bottom of the
mantle is heated by the
core, it starts to rise
causing movements or
currents in the rock. The
result is rather like a pan
of soup coming to the
boil. These currents are
called convection
currents. It is the
convection currents that
force the earth’s plates
to move.
The core
The core has two layers: the
inner core and the outer core.
The inner core is a sphere
composed mainly of iron and
nickel. Although the inner core is
extremely hot (around 6650ºC),
the huge pressures in the centre
of the Earth mean that the inner
core is solid.
The inner core is surrounded by
the outer core. The outer core
has the same composition as the
inner core but it exists as a liquid
instead of a solid due to slightly
lower pressure. Temperatures in
the outer core are estimated to
be around 4700ºC. It is the heat
from the core which generates
convection currents on the
mantle and drives plate
tectonics.
The Crust
On the very outside
of the Earth is the
crust. The crust is
not a continuous
layer, but is made up
of a number of
continental and
oceanic tectonic
plates which fit
together like pieces
of a jigsaw.
The Mantle
Surrounding the core lies a layer known as the
mantle. It reaches temperatures of 3000ºC. The
mantle is composed of dense, rocky material
which ranges from being virtually solid near the
lower boundary with the core, to more soft and
squidgy towards the boundary with the overlying
layer, the crust . Mantle material is less dense
than the core, but still denser than the outer
layers of the earth.
Maps to Show the
Earth’s Tectonic
Plates
The are two types of tectonic
plates forming the earth’s crust continental plates and oceanic
plates. Continental crust, is much
older and far thicker, forming all of
the large land masses. Oceanic
crust is much younger and thinner,
it underlies all the great ocean
basins. The point where two or
more plates meet is known as a
plate boundary
Picture of the
San Andreas
Fault - the
Plate Boundary
Between the
Pacific Plate
and the North
American Plate
Diagram to Show a Cross-Section of the Earth’s Crust
Continental Drift
In 1912 Alfred Wegener published a theory to
explain why the Earth looked like a huge jigsaw. He
found evidence in rocks and fossils found all over the
world which suggested that the continents of the
earth all used to be joined together. He believed
that 225 million years ago the continents were once
joined forming a supercontinent he called Pangaea.
Over 180 million years ago this supercontinent began
to "break up" due to the convection (heat) currents
underneath the earth’s crust. The broken pieces,
which were floating on top of the mantle, began to
drift in all directions in a process called continental
drift.
Diagram to Show Continental
Drift
Plate Tectonics
During the 20th Century, scientists developed Wegener’s ideas and came up with
the theory of Plate Tectonics. The theory of plate tectonics suggested that the
crust of the Earth is split up into seven large plates (or ‘slabs’ of rock) and a few
smaller ones, all of which are able to slowly move around on the Earth's surface.
They float on the semi-molten mantle rocks. The plates are forced to move around
by convection (heat) currents within the very hot rocks beneath the crust. The
crusts may only move a few millimeters a year, but as the earth is about 4000
million years old the effects have been very large!!!
A tectonic plate is like the hard shell on a boiled egg that has been
cracked into pieces or plates!