u4 revision powerpoint
Our Changing Earth
Revision
Earth is made up of four distinct layers:
1. The inner core is in the centre and is the hottest part of the Earth. It is
solid
and made up of iron and nickel with temperatures of up to 5 500°C. With
its
immense heat energy, the inner core is like the engine room of the Earth.
2. The outer core is the layer surrounding the inner core. It is a liquid
layer,
also made up of iron and nickel. It is still extremely hot, with
temperatures
similar to the inner core.
3. The mantle is the widest section of the Earth. It has a thickness of
approximately 2 900 km. The mantle is made up of semi-molten rock
called
magma. In the upper parts of the mantle the rock is hard, but lower down
the rock is soft and beginning to melt.
4. The crust is the outer layer of the earth. It is a thin layer between 0-60
km
thick. The crust is the solid rock layer upon which we live. There are two
different types of crust: continental crust, which carries land, and
oceanic
crust, which carries water
Structure of the Earth
s
crust
mantle
outer core
Innercore
How do the Earth’s plates move?
At DIVERGENT BOUNDARIES the plates move apart.
Pressure that builds up in
the middle of the Earth can push two plates and cause
them to spread apart.
This usually happens under the ocean because the plate
is thinner there, but can also happen on land. This forms
mid-oceanic ridges (in the ocean) and rift
valleys (on land).
At CONVERGENT BOUNDARIES the plates move
towards each other. Pressure can
cause two plates to push together. Over a very long time,
this pushing can create mountains.
At TRANSFORMING BOUNDARIES the plates slide
past each other. Plates can move past each other in
opposite directions, or they can move in the same direction
at different speeds. The plates are pushed together
strongly so, as they move past each other, a lot of
pressure builds up. An earthquake happens when this
pressure is released
How earthquakes form
When tectonic plates move against each other, they do not slide smoothly. The
tectonic plates become stuck, even though they are under pressure to move.
The pressure builds up until suddenly, the tectonic plates give way and move,
releasing the built-up energy. Some of the energy is released in the form of
‘seismic waves (energy that travels in the form of waves through the Earth).
These waves radiate in all directions, including towards the Earth’s surface,
where they are felt as a shaking or displacement of the ground. We call these
events earthquakes. Aftershocks are tremors that follow the largest shock. They
are smaller than the main shock and can continue over a period of weeks,
months, or even years. And can cause tsunami`s, a landslide or intense ground
shaking.
Most earthquakes occur on and adjacent to the boundaries of tectonic plates, but
sometimes they are felt in the middle of tectonic plates. As tectonic plates
continue to move and tectonic plate boundaries change over millions of years,
weakened boundary regions become part of the interior of the tectonic plates.
These zones of weakness within the continents can cause earthquakes in
response to the stresses at the edges of the tectonic plate or inside the Earth’s
crust.
"There are always one or a few
volcanoes acting up somewhere
along the Ring of Fire, and there
are frequent earthquakes. Why?
The main tectonic plates which cover the surface of the
Earth. Pay specific attention to the movement of the plates and
geological features formed due to this movement.
A B
C
Study these pictures carefully. What do you think
has happened here?
(Think about the movement of tectonic plates)
What causes a tsunami?...
A tsunami is a large ocean wave that is
caused by sudden motion on the ocean
floor. This sudden motion could be
an earthquake, a powerful volcanic
eruption, or an underwater landslide.
The impact of a large meteorite could
also cause a tsunami. Tsunamis travel
across the open ocean at great speeds
and build into large deadly waves in the
shallow water of a shoreline.
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