Crust: solid layer, consisting of basalt and
granite, 30 km thick and depth up to 1000 0c
Mantle: Semi solid layer, consisting of
various metals, 2900 km thick,1000- 2500 0c
Outer Core: Liquid layer, consisting
of iron, nickle, oxygen and sulfur,
2300 km thick, 3000- 5000 0c
Inner Core: Solid layer, Consisting
of iron and nickle, 1200 km thick,
5000- 6000 0c
Asthenosphere: hot semi-liquid
in the upper part of the mantle
in continuous movements due to
rock. in the upper
mantle and the
crust that can move.
to describe the
structure of the
Seismic waves: waves of energy caused by the
sudden breaking of rock within the earth. They
are recorded on Seismographs. Two types: Body
wave and surface waves. Body waves travel
through the interior. two types of body waves:
P waves: They are fast and can travel
through solid and liquid so they can be
detectable at the other side of the
earth. They are longitudinal waves.
S waves: Slower waves and can travel
through solid only and not liquid as they are
transverse waves. They are not detectable at
the other side of the earth, therefore, the
earth's interior must contain liquid.
The continental drift
Alfred Wegener hypothesised the earth's continents had
moved. His evidence was based on the fact that all the
continents seemed to fit together like a 'jig-saw'puzzle and
these boundaries were the place he found the same type and
age of fossils. He also found that the mountain ranges on
different continents matched each other.
The convection currents in the
mantle cause the tectonic
plates on the surface of the
earth to move in different
Convection currents: movements
in a circular motion within the
earth's mantle, caused by the
heat of the earth's core. They
occur in the asthenosphere.
The molten magma near the base of the mantle
heats up more than the magma above, becoming
less dense and therefore rising to the top of the
mantle. There it cools down again, becoming more
dense than the hot magma underneath and
sinking to the bottom with the aid of gravity to
repeat the process causing convection currents.
Seafloor spreading: When the convection currents from the
mantle move away from each other, they also move the tectonic
plates on the earth's surface., creating a mid oceanic ridge, a gap
in the plates where the molten magma can rise up fill the gap
and when it cools it creates a new layer of oceanic rock. This
process repeats as the plates get pushed further apart, so the
newest rocks are in the middle with the oldest rocks on the ends.
Dating of the rocks on the mid oceanic ridge
supports the theory of continental drift as the
rocks in the middle are newer than the rocks on
the edges of a mid- oceanic ridge. This means that
the older rocks had to move apart to make room
for the newer rocks to form from molten magma.
This means that the continents must move apart
to form a gap under the ocean.
Volcanoes and Earthquakes
The plate boundaries are the place where
most volcanoes can be found and
earthquakes occur due to the presence of
Volcanoes: The convection currents in the earth's mantle
make the tectonic plates above them move. When the
oceanic and continental boundaries collide as they move
towards each other, they create a subduction zone
where the more dense oceanic crust slides under the
less dense continental crust. Due to the friction of
rubbing past the continental crust, combined with the
heat from the earth's core, the oceanic crust starts to
melt to become molten magma and starts to rise due
to release of heat, and tries to escape and make its way
to the crust. Once the molten magma breaks through
the surface of the earth, it gives rise to a volcano. The
magma that reaches the surface is known as lava. Over
a period of time, the lava cooling off, layer upon layer,
hardens to form rock which build up a volcano.
Subduction: the sideways and
downward movement of the edge
of a plate of the earth's crust into
the mantle beneath another plate.
Earthquakes: The convection currents
underneath the earth's surface move the
tectonic plates towards each other. They come
really close together and the rocky plates press
against each other, creating friction which
opposes the movement of the jagged rocks. This
causes a build up of pressure, which releases
when it is too much to stop the resistance of
the rock. This release of pressure causes the
sudden movement of the rock as it breaks and
causes an earthquake.
The Himalayas: The teectonic plates are moved
towards each other by the convection currents.
When neither of them subduct after collision, the
boundaries are crumpled by the collision. This
fractures the crust rocks and the force pushes
them upwards to form a chain of mountains.
This was how the Himalaya mountnain range
formed when the Indian plate collided with the
Impacts of a volcano
Impacts of an earthquake
Seismographs: Seismology is the study of earthquakes and
their shock waves. The sudden release of energy caused by
the movement of the tectonic plates, sends out shock waves
which are detected and recorded by a seismometer. It is an
internal mass attached to an immobile frame. The swinging
of the mass caused by the movement of the earth helps
record the size and frequency of the waves. These recordings
can be later studied and conclusions can be formed according
to the patterns that form on the wave graphs.
Magnetometers: When pressure builds up near a fault line, the heat
generated changes the magnetism of the rocks near it. This change in the
Earth's Magnetic feild is measured and recorded using a magnetometer
which is placed near the fault line for monitoring. Any large metallic
objects can affect the readings, so remote areas give more reliable results.
They can also be towed behind in boats or aircraft to provide a reading
for a larger area. The bigger the signal the bigger the earthquake is.
Seismic survey: send sound waves into the earth and use the time
taken for the wave to bounce back to calculate the structure and
the materials in the layers of the Earth as the waves are reflected
differently at the point of chance in the physical properties of the
material. 3D seismic surveys use different observation points on a
carefully marked grid to precisely locate different materials and
form a 3D cube image of the location. These are commonly used to
find minerals in the oceans