Notes

1. UNIT 2. The Earth’s Internal Energy
2º ESO
SCIENCE
UD 2 THE EARTH’S INTERNAL ENERGY
1. GEOLOGIC PROCESSES
2. INTERNAL EARTH’S STRUCTURE
2.1. Geochemical or static model
2.2. Dynamic model
3. TEMPERATURE AND PRESSURE INSIDE EARTH
4. WHAT IS THE CAUSE OF EARTH’S INTERNAL ACTIVITY?
5. CONTINENTAL DRIFT THEORY
6. PLATE TECTONIC THEORY
7. VOLCANOES RISKS, PREDICTION AND PREVENTION
8. EARTHQUAKES: RISKS, PREDICTION AND PREVENTION
9. FOLDS AND FAULTS
1. GEOLOGYC PROCESSES
The Earth is a dynamic planet, this is, it is changing constantly as a consequence of internal and
external geologic processes (IGP and EGP)
PGI (IGP): they are produced by the Earth’s internal energy which produces the movement of tectonic
plates and as a result causes or provokes earthquakes, volcanoes, mountain formation... These
processes are called CONSTRUCTIVE GEOLOGIC PROCESSES (“they make relief”)
PGE (EGP): they are produced by the Earth’s external energy (solar energy) and the interaction with
atmosphere and hydrosphere. These processes are called DESTRUCTIVE GEOLOGIC PROCESSES (“they
destroy relief”)
So, relief is the consequence of both processes IGP and EPG
2. INTERNAL EARTH’S STRUCTURE
We are going to study the Geosphere. We must difference two models which explain the internal
structure of the Geosphere:
2.1. Geochemical or static model
2.2. Dynamic model
2.1. Geochemical or static model
a. Crust: is the thinner and solid layer of Geosphere, made up of rocks and minerals, it is the
outermost part of Geosphere.
There are two types or crust:
 Continental crust: the rocky layer that forms the continents and the shallow areas of oceans
(about 200m deep): continental shelf.
 Its thickness varies between 10 km (below the coast) and 70km (bellow great
mountains).
 Its more abundant rock is Granite (plutonic rock),although we can find metamorphic
and sedimentary rocks, too
 It’s very old (0- 4000 million years old)
 Oceanic crust: the rocky layer beneath the oceans.
 Its thickness varies between 5 and 8 km.
 It’s younger than the continental crust: 0- 180 million years old.
 The sea floor shows the following relief:
Continental shelf: it´s a part of continent that extends beyond shoreline, under the
ocean. (it belongs to continent)

2. UNIT 2. The Earth’s Internal Energy
2º ESO
SCIENCE
Continental slope: it´s a big depression that extends from continental shelf to the
sea floor.
Abyssal plain: it´s the bottom of the ocean where you can find the flattest areas on
the Earth and mountains, volcanoes, Guyots…
Mid ocean ridge: it´s a huge mountain chain (6000km long and 2000km wide)
located in the centre of many of the Earth´s oceans. The axis is called ocean rift.
Deep sea trench: it´s a huge depression on the sea floor formed when a plate sinks
under another plate.
b. Mantle: it’s the layer placed beneath crust (to 2900km deep), it´s denser than crust.
It contains two areas:
 Upper mantle: (from crust to 700-1000km deep)is less dense than lower mantle and it
is semi-molten
 Lower mantle: (from upper mantle to 2900km) is denser than upper mantle and more
solid.
c. Core: it is the innermost part of Geosphere (from 2900km to 6370 km deep). It is the densest
layer because it is made up of iron and nickel. It contains two areas:
 Outer core: (from 2900 to 5120km) it is molten.
 Inner core: (from 5120 to 6730km) it is solid.
2.2. Dynamic model: this model divides the Earth in three parts, but the scientists have realized that
one of them, the asthenosphere, is not a continuous layer, and for that reason it is no longer
included in the model
This model appears to explain the movement of tectonic plates. It divides Geosphere into “4”
layers:
a. Lithosphere: it is a rigid and fragmented layer that includes the crust and the upper section of
the mantle (up to 100 km deep). It is divided into lithospheric plates: the most important six
plates are: American plate, African plate, Eurasian plate, Indo-Australian plate, Pacific plate,
Antarctic plate. Lithosferic plates are fragments of crust located on the mantle. The
Lithospheric plates are continuously moving, crashing into each other at some points and
separating at others.
b. Asthenosphere: is located beneath lithosphere, it’s a no continuous layer, it’s discontinuous.
It’s rigid but has a fluid behaviour (REID)

3. UNIT 2. The Earth’s Internal Energy
2º ESO
SCIENCE
c. Mesosphere: it is the layer located
right below the lithosphereasthenosphere. Its lower bound is
2900 km deep. It's the layer where
convection currents are formed.
Thickness “400”-2900km
d. Endosphere: it is the innermost
layer of our planet. It is a sphere
whose center is 6370 km deep and
whose surface in not regular due to
convection currents that take place
in it. It matches with core in static
model
This model, dynamic model, tries to
explain
the
movement
of
lithospheric plates.
3. TEMPERATURE AND PRESSURE INSIDE EARTH
Geothermal gradient is the rate of increasing temperature with respect to increasing depth in the
Earth's interior.
4. What is the cause of Earth’s internal activity? Causa de la actividad interna terrestre
The cause is the transmission of heat from internal areas to external areas of the Earth, by means of
convection currents. Heat from the Earth’s core heats up material of lower mantle, these materials
rise because they are lighter. When they rise, they cool down and fall because they are heavier. So
convection currents are formed.
5. CONTINENTAL DRIFT THEORY Teoría de la Deriva continental de Wegener
Continental drift is the theory proposed by A. Wegener to explain the lithospheric plates movement.
In 1915, Alfred Wegener (1880-1930) first proposed the theory of “Continental drift”, which states
(show, say) that parts of the Earth’s crust slowly drift atop a liquid core. Wegener hypothesized that
there was an original, gigantic super continent 200 million years ago, which he named Pangaea,
meaning “All-Earth”. Pangaea was a super continent made up of all the Earth’s land masses.
Pangaea started to break up into two smaller super continents, called Laurasia and Gondwanaland. It
formed the continents Gondwanaland and Laurasia, separated by the Tethys Sea. By the end of the
Cretaceous period, the continents were separating into land masses that are our continents.
According to this theory, 200 million years ago, there was a gigantic super continent called Pangea (allEarth). Pangea started to break up into smaller super continents to form the continents which we
know nowadays. Since then, continents go on moving and changing their positions.
Which are the evidences of continental drift theory?
 The shape of the continents fit as a puzzle
 Similar sequences of rock and geologic material in places located too far away nowadays
 Distribution of similar fossils in places located too far away nowadays
 Evidences of tropical climates in the current polar areas and vice versa

4. UNIT 2. The Earth’s Internal Energy
2º ESO
SCIENCE
6. PLATE TECTONIC THEORY Tectónica de placas
Lithospheric plates move on Asthenosphere as a consequence of the convection currents produced by
the Earth’s internal heat and its semi-molten materials
We must difference three types of plate boundaries
 Convergent boundaries: the plates move toward each other. In general, one of the plates
subsides beneath other and sinks inside the mantle. These boundaries are called destructive
boundaries because they destroy lithosphere.
 Divergent boundaries: the plates move away from each other because of material that rises
from mantle through the rift (in ridge). These boundaries are called constructive boundaries
because they form new lithosphere.
 Transform fault boundaries: plates slide past each other, they move laterally in opposite
directions. No lithosphere is created or destroyed
The movements of plates produce geological processes such as volcanoes, earthquakes, mountain
ranges and other changes that alter the Earth’s surface
7. VOLCANOES : RISKS, PREDICTION AND PREVENTION
7.1. Volcanoes:
Definition: volcano is an opening of the surface of the Earth where gases, liquid and solid from the
lithosphere are released.
Parts of a typical volcano:
Magma chamber: deep area where magma is accumulated.
Pipe (chimney ): conduit magma travels through
Crater: mouth of volcano where pipe finishes.
Volcanic cone: mountain-shaped structure formed by accumulation of volcanic material.
Volcanic materials: three types:
Solids:
 Ash
 Lapilli
 Bomb
Liquids: lava (lava: molten rocks that erupt)
Gaseous
Types of volcanoes: The violence and danger of a volcanic eruption depends on magma viscosity
and magma gaseous composition. "Strombolian," "Vulcanian," "Vesuvian," "Pelean," "Hawaiian,"
and others (spanish)
7.2. Risk, prediction and prevention (spanish)
8. EARTHQUAKES: RISKS, PREDICTION AND PREVENTION
8.1. Earthquakes:
They are vibratory movement of the Earth’s crust produced by releasing of accumulated energy
inside the Earth because of the contact/touch of tectonic plates.

5. UNIT 2. The Earth’s Internal Energy
2º ESO
SCIENCE
The location below the Earth’s surface where the earthquake starts is called the focus or
hypocenter, and the location directly above it on the surface of the Earth, is called the epicentre
Seismic waves:
Seismograph (Sismógrafo): it is the instrument that we use to study seismic waves
Seismogram (Sismograma): it is the graphic that show the seismic waves.
SEISMOGRAM
SEISMOGRAPH
There are three types of waves:
 P waves or primary waves: They travel faster than other waves through the earth to arrive
at seismograph stations first. They displace the ground longitudinal to the propagation of
waves. Theses waves can travel through any type of material fluid or solid
 S waves or secondary waves: They arrive at seismograph station after primary waves; they
displace ground perpendicular to the propagation of wave. These waves can travel only
through solids
 Surface waves: L and R
Magnitude and Intensity:
 Magnitude scale: It is the quantity of released energy from focus. It is measured on Richter
scale.

6. UNIT 2. The Earth’s Internal Energy

2º ESO
SCIENCE
Intensity: it is the magnitude that measures the strength with which an earthquake shakes
the ground. It is measured on Mercali scale.
8.2. Risk, prediction and prevention (spanish)
9. FOLDS AND FAULTS
9.1. Fold: they are the result of compression strengths on the ground. As a consequence concave and
convex waves are formed.
9.2. Fault: they are rifts on the ground which imply movement (displacement) of the blocks formed