The document summarizes the structure and composition of the Earth. It describes the three main layers - crust, mantle, and core. It then explains plate tectonics theory and how the movement of tectonic plates causes volcanic activity and earthquakes. The crust is made up of both emerged and submerged lands, including continents and oceans. The Earth's surface relief is shaped by both internal forces like plate movements and external agents like wind and water.

1.  1º

2. The Earth is divided into layers:
 The crust is the surface layer. It is a thin,
solid layer made of rock. The Earth’s crust
has a solid part (continents), and a liquid
part (oceans).
 The mantle is the intermediate layer. This
layer is almost 85 % of the Earth’s volume. It
includes magma, which is molten rock.
 The core is the deepest layer.

4.  In 1912, Alfred Wegener outlined his
continental drift theory. According to this
theory 200 millions years ago there was a
single giant land mass (one supercontinent),
called Pangaea. This Pangaea was
surrounded by a single ocean, called
Tethys Sea.

6.  The Pangaea broke up, forming the continents.
 These continents are no fixed, but they are
moving, because the crust (the Earth’s layer
where we live) is divided into several plates,
called tectonic plates.
 These plates are moving slowly over the mantle.
They move at a speed of 2 to 10 centimetres per
year.

9.  Some tectonic plates move apart, while
others collide.
 Where plates collide the Earth’s surface
often undulates and folds are created.
 The Earth’s crust sometimes fractures if the
surface where plates collide is extremely
rigid. Then, faults are created, and blocks
rise or sink.

12.  The movement of tectonic plates can
produce volcanoes and
earthquakes.

13.  A volcano is an opening in the planet surface
or crust which allows hot magma to
escape. When magma comes out of a
volcano, it is called lava.
 When a volcano erupts, it also ejects ash
and gases.
 Volcanic eruptions under the sea can form
islands such as the Canary Islands.

14.  Magma is pushed up
by the Earth’s internal
forces.
 It rises through a pipe
or a vent.
 It comes out through a
crater.
 Volcanic cones are
the result of lava
accumulating outside
the opening.

15.  When two tectonic plates crash, there is a
release of energy that makes the ground
vibrate. This vibration is called an
earthquake or seism.
 The vibration can be very violent or almost
unnoticeable.
 If an earthquake occurs on the ocean floor
can produce huge waves called
tsunamis.

16.  There are about half a million earthquakes
each year, but only about a thousand cause
any serious damage.
 During an earthquake the shock waves
spread out from a point below the surface
that is called the focus. The point at ground
level, directly above the focus, is called the
epicentre.
 The Richter scale and Mercalli scale are
both used to measure the strength of a
quake.

18. On the Earth’s crust there are emerged and
submerged lands:
Continents occupy 30% of the land
surface and are surrounded by oceans and
seas. There are six continents: Asia,
America, Africa, Antarctica, Europe
and Australia.
 Most of the emerged land is in the northern
hemisphere.

19. Oceans are large masses of salt water.
There are five oceans: The Pacific Ocean,
The Atlantic Ocean, The Indian Ocean,
The Arctic Ocean and the Southern
Ocean.
 Most oceans are in the southern hemisphere.

22.  The Earth’s surface isn’t flat, there are
mountains, plains, plateaux, valleys, etc. The
relief of the continents is very diversed.
 The relief is the result of the internal
forces of the Earth(plate movements,
volcanoes, earthquakes, etc.) and external
agents (wind, rain, temperature, rivers,
waves, ice... and human-beings).