1 universe earth-2012

Human species in the
Universe
1. The Universe and the Earth
2. The origin of life and first organisms
3. Creationism and evolutionism: the natural selection
4. Hominids: the human evolution

What do you know about it?
 Ptolemy (90-168 AD) geocentric model was accepted for more
than 1500 years. Which evidences do we have that Ptolemaic
model is wrong?
 Which is the actual situation of the Earth in the whole Universe?
 Why do you think that scientific theories change along the time?
Is it reasonable to assert that as science changes along the time
that makes science uncertain? DISCUSS THE ANSWER
 Is the Universe unchangeable? Describe some evidences to
support your opinion
 How did the Universe start? How long ago did it begin? What
evidences do we have?
 Is it possible that nowadays mountains, were a million years ago
at the ocean floor? EXPLAIN
 Is astrology a science? Can we trust in horoscopes? DISCUSS
YOUR OPINION

Why Ptolemaic model was finally
rejected?
 Geocentric model explained the main aspects of the stars
behavior and placed the Earth at the center of the Universe.
Why was it changed?
 It had hard problems to explain the wandering motion of
PLANETS
 The new heliocentric model placed the Sun at the center with
planets turning around it in elliptical orbits
 The HELIOCENTRIC model was easier and more precise
 It was possible to make more accurate and exact predictions
 It was completely compatible with NEWTON’s laws

Let’s explore the solar system
 A first approach: THE PLANISFERE
 It is a map used to describe the apparent motion of the stars
as we see them with our naked eyes: the Moon, the Sun, the
wandering stars or planets and the fixed stars
 In order to learn how does it work, we will use the
STELLARIUM simulator, which is a freeware to represent
quite exactly the motion of the celestial vault from any
terrestrial point of view, date and time

WEBS about Astronomy:
 http://www.stellarium.org/ca/
 http://www.nasa.gov
 http://www.atlasoftheuniverse.com/catala/
 http://www.iac.es/
 http://heavens-above.com/
 http://www.google.es/intl/es/earth/index.html
 http://redblogs.org/tamano-relativo-de-los-objetos-en-el-universo-
video/

 Since ancient times we know about stars visible with our
naked eyes: the Moon, the Sun, the planets Mercury, Venus,
Mars, Jupiter and Saturn
 The invention of the telescope in 1610 allowed the discovery
of the four biggest Jupiter satellites, the sunspots and the
Moon craters. These observations supported the heliocentric
model proposed by Copernicus and defended by Galileo and
Kepler
 More powerful telescopes allowed to observe much more stars
invisible with our naked eyes, and even the planets Uranus
(1781) and Neptune (1846)
 Beyond Neptune there are the trans-Neptunian objects. There
lie the comets and the dwarf planets or plutoids: Pluto (1930)
and Charon (1978) and Eris (2005)
 The solar system boundary is approximately 15 000 million km
far from the Sun. The nearest star, Proxima Centauri, is
40 000 000 million km (some 4 light-years) away

Top dates in space exploration
 1957 First man made satellite Sputnik
 1961 Yuri Gagarin, first astronaut sent to space
 1962 Space probe Mariner 2 explores Venus
 1969 Neil Armstrong sets foot on the Moon
 1973 Space probe Pioneer 10 explores Jupiter and Saturn
 1976 Space probes Viking lands on Mars
 1986 Space probe Giotto approaches comet Halley
 1990 Hubble Space Telescope is carried into orbit
 1995 First planet beyond the solar system discovered
 1998 The building of the International Space Station starts
 2004 Space probe Cassini-Huygens lands on Titan (the
biggest of Saturn satellites)

International Space Station
(1998)

The discovery of new
planetoids
1. 1 hour = 3 600 s;
13.5 hours X 3 600 s = 48 600 seconds
300 000 km/s X 48 600 s = 14 580 000 000 km =
14 580 million km
2. Eris is bigger than Pluto, that’s why we should consider it a
new planet and there would be ten at the solar system. On
the contrary, neither Eris nor Pluto would be planets. What
would they be then? On August 24, 2006, the IAU agreed
a NEW DEFINITION of planet, excluding both Pluto and
Eris and including only: Mercury, Venus, the Earth, Mars,
Jupiter, Saturn, Uranus and Neptune

2. Eris, Pluto and Ceres (the biggest of asteroids) were
included in a new category, dwarf planets, later renamed
as PLUTOIDS
3. AGAINST: Our planet urgently needs now better
challenges than space exploration. Poverty eradication,
famine or environmental problems due to climatic change
are preferred. But we can also argue IN FAVOUR: Space
exploration promotes the enhancement of our living
space or the settlement of colonies in other stars; grant
access to new resources of economic interest; lead to
new scientific discoveries of unpredictable importance; a
better understanding of our environment and avoid
some catastrophe (as the impact of a great meteorite) that
could endanger our survival as species
http://ca.wikipedia.org/wiki/Fitxer:Animation_showing_movement_of_2003_UB313.gif

Are there any planets beyond
the solar system?
 One of the outmost discoveries in recent years answers the
question about the existence of planetary bodies in other
stars, the so called EXOPLANETS
 New techniques have allowed the detection of these tiny
objects while they turn around their star and partially eclipse
its light. Only in 2011, 188 exo-planets were detected
 The major interest focus in inhabitable planets, what means
more specific conditions to their features, in mass of star and
distance from the star. They are called earth type planets
 The search is also for the so called hot Jupiter type, the ones
with a big size, but so close to the star that they are very hot

Hot Jupiter type
 Some planets…

A burst of galaxies
 In a place far from artificial light in a bright night, our friends
Marc and Paula should have seen a white line, with a diffuse
shape, across the sky
 It is the Milky Way, that every people have considered to have
a mythical origin. For ancient Greeks it was a milk jet from
goddess Hera. Medieval pilgrims thought it was showing Saint
James’s way. For Arabian and Chinese it was a big river
flowing across the sky and African people Kung thought it was
the backbone of the night
 WHAT IS THE MILKY WAY ACTUALLY?

The Milky Way is our galaxy
 Galileo was the first one to observe it with the telescope. He
discovered that there were thousands of stars, so many and
so weak that they appear like a milky strip (galaxy comes
from: γαλα (gala) which is the Greek word for milk). Most of
the stars visible from the Earth concentrate in a narrow strip
 Along the 18th century astronomers proposed that it could be
because the stars gathered in a spinning disc, stick together
by the force of gravity
 At the beginning of the 20th century, the study of spiral
nebulae, like Andromeda, opened a great discussion about
whether they were inside the Milky Way or not

 In 1923, Edwin Hubble could identify individual stars in some
spiral nebulae
 The brightness of a star depends on its luminosity (the
amount of light emitted) and on the distance from where it is
 Hubble identified one class of stars, the so called Cepheid
variables, that have always a constant luminosity. This made
possible to appreciate the distance to those spiral nebulae
and demonstrate that they did not belong to the Milky Way
 So SPIRAL NEBULAE are independent galaxies as it is ours.
Now we can observe hundreds of thousands of millions of
galaxies

 Nowadays we consider that the Milky Way has a 100 000
light-years diameter and includes hundreds of thousands of
millions of stars spinning slowly and making one turn in 250
million years
 The Sun is nothing but an ordinary star, situated in one of the
spiral arms
 Galaxies are separated between them by an empty space of
millions of light-years and can have some satellite galaxies

Expansion of the Universe:
Hubble law and the Big Bang
 An ambulance siren does not sound the same when it
approaches than when it goes away
 This is because of the DOPPLER effect: when an object in
motion emits a wave, the frequency we receive from it varies
depending on its speed
 The same effect happens with light, which is a wave too, but
we need higher speeds to detect it

Doppler effect: waves
produced in a moving focus

Doppler effect: red shift of light
coming from galaxies
z = v / c
The higher z,
the higher the red shift

Hubble law
 Doppler effect and the red shift of spectral lines emitted by
light coming from galaxies were used to determine the
relative motion of outer galaxies compared to ours
 The first surprise was the discovery that ALL GALAXIES
MOVE AWAY
 The second one was in 1929, when the distance to different
galaxies was compared to their relative speed from ours:
when one plotted the data in a chart these data fitted aligned
 THE FURTHER A GALAXY IS, THE FASTER IT MOVES
AWAY FROM US (HUBBLE LAW)
 THE UNIVERSE IS UNDER EXPANSION

A POSSIBLE EXPLANATION
FOR HUBBLE LAW :
EXPANSION OF THE UNIVERSE
CHART V / D :
HUBBLE LAW
1 Mpc = 3.26 Mly = 3.086·1022 m
V = H0·D
Hubble constant H0 :
0.000 021 5 km/s/ly

The Big Bang hypothesis
 Since the Universe is spreading, if we move back in time we
should find galaxies closer and closer, until we reach the
moment in which all the matter of the Universe was
concentrated in one single point
 That would be the moment when the Universe began, in a
very big explosion known as the Big Bang. The best
estimations in 2010 consider that the Big Bang happened
some 13 700 million years ago
 Physicists consider that if this titanic explosion actually
happened, we should still receive its residual radiation at
present-day

Background radiation
 This radiation, that would be weaker than a microwave oven
emission, was eventually detected in 1965 by Arno Penzias
and Robert Wilson accidentally. This discovery means that
the Big Bang Theory has been able to make precise and
certain predictions, one of the outmost criterion to assess the
validity of a scientific theory

From Big Bang to Big Crunch?
 The Theory of Relativity predicts that the expansion of the
Universe should be stopped by the attraction of the
gravitational force
 Some years ago an attempt was made to find out if the
Universe had enough matter to stop expansion and collapse
again, in some sort of Big Crunch or big implosion, or
otherwise it would expand indefinitely
 The observation of galaxies very far away revealed in 1998
that the expansion of the Universe was accelerating
 The interpretation of this phenomenon is a matter to debate
among scientists, many of them say there is a dark energy
making possible the Universe to enhance
 Another present-day mystery of the Universe is the nature of
dark matter which seems to content some 23 % of the
Universe whole mass

The Pavo (the Peacock) cluster
1. It is not. As the cluster is 180 million light-years away from
us, the light we see has taken 180 million years to reach
the Earth. Thus we see the Pavo cluster as it was 180
million years ago
2. It moves away because the whole Universe is expanding,
as a consequence of the Big Bang or big explosion from
which the Universe began
3. Speed = Distance X H0 = 180 000 000 light-years X
0.000 021 5 km/s/ly = 3 870 km/s (We can also use the
chart on page 17 in our textbook)

4. Time to arrive to Proxima Centauri:
P. Centauri is 40 billions of billions of km or 4 ly
40 000 000 000 000 km / 3 000 km/s = 13 333 333 333 s
= 3 700 000 hours = 154 321 days = 423 years
(Otherwise: the spacecraft travels 1/100 fold the speed of
light, if light takes 4 years, the spacecraft will take 400
years)
Time to get across the Milky Way:
If the spacecraft is 100 fold slower than light, it will take 10
million years to get across the MW which is 100 000 ly wide
Time to arrive to the Pavo cluster:
1st ANSWER: The cluster is 180 million ly ago, so the
spacecraft will take 18 000 million years
RIGHT ANSWER: The spacecraft WILL NEVER ARRIVE
THERE, because it moves with a slower speed than the
cluster moves away from us, and along time that speed will
even go faster

Where does energy of stars
come from?
 Stars are placed light-years away, but we can see them
because of the huge amount of energy they release
 They are in majority formed by elements hydrogen (H) and
helium (He), whose atoms are the smaller and simpler
 At the beginning of the Universe all matter was hydrogen and
the other elements were formed later on inside the stars
 The origin of stellar energy lies in NUCLEAR FUSION
REACTIONS. When two or more nuclei of H fuse we get one
of He and a lot of energy is released. In one star, the energy
produced every second by this process equals the burst of a
million hydrogen bombs
 Temperatures of 40 million Kelvin are generated

2
1H + 3
1H  4
2He + 1
0n

What are stars made of?
 Atoms of the elements heated to a very high temperature emit a
feature light. After analyzing the light coming from a star, we
can deduce which chemical elements does it content. These
aspects are studied in the Physical branch known as
SPECTROSCOPY

Life of stars
 Stars and planets accompanying them are originated in
clouds of interstellar gas. When they are big enough, they
start to contract because of gravitational force and heat up to
reach the appropriate temperature to start de nuclear fusion
reactions of hydrogen atoms. Then a big amount of energy is
released, the former gas cloud expands, it starts shining and
becomes a STAR
 The “life” of the star and the way it comes to an end depend
on its initial mass. Most of stars have a mass similar to our
Sun and calculations predict they can fuse hydrogen for
about 10 000 000 000 years
 The Sun has already been shining for about half this time

Gas cloud at the Aquila nebula
Space telescope Hubble

Does the
Sun have
some dark
matter?

 There is a time when hydrogen from the star nucleus comes
to an end. Then a new fusion starts in hydrogen from the
outer layers, consequently it inflates, its luminosity increases
and becomes a RED GIANT STAR. At the end of this step it
fuses helium and originates carbon and oxygen. This extends
a bit the life of the star, but as helium also comes to an end,
the star fades and contracts until it becomes a WHITE
DWARF STAR
 When the Sun become a red giant, in some five thousand
million years, it will swallow Mercury and Venus, and maybe
even the Earth too. In any case, million years before that
happens temperature in our planet would have increased so
much that it will be impossible any way of life known: oceans
will evaporate and atmosphere gases will escape to outer
space. Later on, the Sun will start fading until it will not emit
light anymore

The destiny of the largest stars
 Stars with a mass ninefold bigger than the Sun live much less time:
only one or two million years, because their temperature is much
higher and they fuse hydrogen more quickly
 These stars form much heavier elements by fusion, like iron, gold or
uranium
 At the moment when their fuel is out, giant stars burst in a huge
explosion named SUPERNOVA
 During several months they shine as much as millions of normal
stars, they release out a big part of their matter and when they fade
they finally become a NEUTRON STAR or, if they are exceptionally
large, a BLACK HOLE
 Matter released by supernovae may finally become part of
interstellar gas clouds and stars in the next generation may content
heavy elements originated in a supernova

Supernovae
 In 1054 AD a new star appeared at the constellation of
Taurus. This star was visible by the daylight, and by night it
was even possible to read because of its light. After a year it
faded. This event was registered by astronomers at different
parts of the world
 The picture in slide before, taken with the Hubble space
telescope, shows the Crab Nebula, which are present-day
rests of the 1054 AD supernova, placed 7000 ly away from
the Earth. The different colored filaments show the presence
of hydrogen, sulfur and oxygen. There is a neutron star in
the middle spinning around itself thirty times per second and
emitting radiation pulses
 Matter in a neutron star is incredibly concentrated: a spoonful
of a neutron star weighs alike a terrestrial mountain
 With modern telescopes tenths of supernovae are discovered
every year, most of them in outer galaxies

NGC 4261 – Virgo 100 million ly
Component of a binary system
transformed into a black hole
Black hole in the middle of a cluster Black hole at Cygnus X-1

Black holes
 In 1971 a big source of X-rays was discovered at the
constellation of Cygnus (the Swan). The source, named
Cygnus X-1, must be some 300 km wide
 Gravity attraction acting on a nearby star allowed to calculate
its mass: tenfold bigger than the Sun
 An object with such a high density must be a BLACK HOLE:
a place where gravity is of such intensity that nothing can
escape from its surface, not even light
 When matter swallowed by the black hole from the nearby
star falls, it accelerates and heats until the emission of X-rays
 They are strange places, singularities in space-time where
the laws of Physics are not valid anymore. If something falls
into a black hole, it never goes out

Are we made of stardust?
1. The Sun gets its energy by means of nuclear fusion reactions,
basically by fusing H atoms and producing He
2. After starting to shine like a STAR, the Sun has been fusing H
into He for some 5 000 million years and it is predictable that it
will continue the next 5 000 million years. Then H will come to
an end and He will start to fuse, making O and C, so its volume
will enhance to become a RED GIANT STAR. When He ends,
the Sun will start to contract and cool to become a WHITE
DWARF STAR. Thus the phases are: “NORMAL” STAR – RED
GIANT – WHITE DWARF

3. The Sun won’t go through these phases until 5 000 million years
later. It’s so much time that if the descendants of our species still
survive they must have colonized other stellar systems and will
be able, in part, to escape from the violent final of our solar
system
4. The Sun itself can’t become neither a black hole nor a neutron
star because it has not enough mass to get it. The only stars to
become those objects have masses ninefold the Sun mass.
5. H is the original element of the Universe and was formed just
after the Big Bang. C and O are formed in red giants, stars that
are about to finish their fuel. Fe is formed in a very big star. So
Fe, H, C and O, elements found in living beings, were all formed
in stars of a generation previous to the Sun itself, and these
stars released those elements at the end of their own cycle
6. Much of the atoms that form our body (oxygen, carbon, iron,
etc.) have belonged to previous stars. According to this, the
sentence is true

What is astrology?
 Astrology is a knowledge that claims to know and predict
people’s personality and important events in their lives. For
that purpose, it is based on the stars positions and their
motion, considering one person’s birth date
 In ancient times and during the Middle Ages, astronomy and
astrology developed together and they were usually practiced
by the same researchers: Ptolemy, who described the
geocentric model, wrote also some books about astrology
and many astronomers earned a living by making astrological
predictions to several kings and princes

 Astronomy and astrology began to split since the approval of the
heliocentric model at the time of Kepler
 Since then on, astronomy has been developing, as any other
science, while astrology is still based in the same old principles
 Astronomy has incorporated the discovery of new planets and
galaxies, has postulated the expansion of the Universe and its
origin from a big explosion, has developed coherently with
Physics and Mathematics and has been able to calculate
distances, velocities and chronologies with high precision
 Meanwhile, astrology is still based in the same twelve zodiac
signs (without considering that their position has changed since
the times of Ptolemy and that, in fact, they are not twelve but
thirteen), the same old seven planets (including the Moon and
the Sun) and it keeps the idea that the whole Universe turns
around the Earth (so it uses expressions like “Mars is in Aries”).
Many astrologists still talk about the four elements from ancient
Philosophy (earth, water, air, fire)

The zodiac: The Animal house
Astrology is now unconnected
from modern science. According to astrologists,
the position of Mars at the moment of the birth may
have influence in one person’s life, but how
could a star exercise such an influence?

 Many people is born in a closed room and light reflected by this
planet cannot reach them. The only sort of influence known
coming from Mars is gravity, but Mars is so far away that its
gravitational effect upon us is sixfold lower than that of the
midwife helping the childbirth
 Its ability to predict is very doubtful. Very often, two twins, born
in the same place with some minutes of delay, have had very
different lives: that is, one of them died in childhood of a car
accident while the other got unto oldness. When quite
controlled tests are done, astrologists are unable to predict the
personality and future of people only known by their date and
place of birth
 Psychologists have discovered that people behave in the way
they believe they are expected to. If we are usually said to be
impetuous and energetic, we will probably behave so. This is
the most efficient way how horoscopes influence our lives

Can we rely on horoscopes?
1. In some signs, predictions are incompatible. You can
easily check it in Aries, Leo and Libra
2. They aren’t but general ambiguous predictions, and could
apply to many different situations, like: “There are some
affective tensions about you that could not have you in
focus but involve you in some way”. Everyday practically
everybody comes across with situations that could fit to the
prediction said before
3. They are based on the situation of different stars (the
Moon, Mars, the Sun, etc.) in a particular position, as we
see them from the Earth. These circumstances cannot act
on people’s life by any well known means

4. Some possible arguments IN FAVOUR are:
Astrology is a very old kind of knowledge.
Some people think that predictions work.
Some possible arguments AGAINST are:
Astrology has not changed in two thousand years. It is so
reliable as medicine practiced two thousand years ago. It is
not a science, it is only a PSEUDOSCIENCE.
Its theoretical foundations have no relation with modern
science. It supposes that the Earth is the center of the
Universe. It is based in seven planets, and there are some
more (considering the Moon and the Sun as planets). It
doesn’t take into account the changes in the stars positions
the last two thousand years. It ignores galaxies, black
holes, supernovae, etc.
Astrological predictions are inaccurate, general and
frequently contradictory.
Astrologists are unable to predict people’s personality by
only knowing the time and place of birth.
Astrology is an obsolete discipline with no reliability at all.

The Earth’s origin:
the solar system formation
 According to the nebular theory, the solar system originated
some 4 600 million years ago, coming from a cloud made of
gas and dust, similar to the Aquila nebula that we have seen
before
 The gas and dust cloud contracted because of gravitational
attraction, probably due to the explosion of a nearby
supernova. While it was contracting, the gas cloud started to
turn around itself faster and faster
 Most of the matter remained condensed at the center of the
cloud where the Sun was formed. Matter turning outside
started crashing and gathered in fragments bigger and bigger
until planets were born as we know them now

The nebular theory explains
the origin of the solar system
The Moon’s origin is
related to the impact
of a big planetoid called
Theia, like Selene’s mother

The Moon’s formation
 Today’s most accepted theory of the Moon’s origin explains
that our satellite was formed as a consequence of the impact
of a planetoid, whose mass was similar to Mars, with the
early Earth. In this theory the planetoid is named Theia, after
the mythological character who was Selene’s mother, being
Selene the goddess that represented the Moon
 Collision should have torn off a huge amount of materials,
that would have gathered because of gravitational attraction
to form the new satellite: the Moon. This theory could justify
the fact that the Moon contains materials very similar to the
ones found at the Earth’s surface

The process of the Earth’s
formation
 Soon after its formation, the Earth had an atmosphere with a
few gases and suffered the continuous arrival of meteorites
to its surface
 It also showed a very intense volcanic activity, because of
that it had an external temperature of hundreds of centigrade
degrees
 At that period the planet materials arranged according to its
decreasing density: the heaviest in the core and the lightest
outside. The Earth’s surface slowly cooled down, water
steam condensed and oceans appeared

The fall of meteorites and
volcanic eruptions have become
less frequent but they still happen
nowadays
The picture shows how should be the
Pre-cambrian Earth, some 1 000 million years
ago. There are volcanoes in eruption and
early forms of life (green algae)

The Earth’s layers
 Humans have been able to observe the Earth’s surface,
atmosphere and oceans. We have dug wells and shafts, but
the deepest shaft ever dug until now is at the Kola peninsula
(Russia) and it reaches only 12 262 m deep. Compared to the
Earth radius (6 378 km), we realize that we have hardly
scratched the planet’s surfaces. How can we learn about what
is inside?
 The first clue is given by noting that at the outer Earth’s
surface, TEMPERATURE INCREASES 3 °C EVERY 100 m,
INSIDE THE PLANET. This happens because there is heat
inside the planet, so high that it can melt rocks and generate
magma

 If we consider that magma ejected by volcanoes is some 1 000
°C hot, we can infer that temperature inside the Earth must be
about thousands of centigrade degrees
 Another clue is given by the TERRESTRIAL MAGNETIC FIELD,
what makes the compass needle to point to the north. The most
accurate explanation to understand this magnetic field says that it
is originated by the electron motion inside the planet, in a zone
with a lot of IRON
 A very important source of information about the Earth composition
comes from METEORITES
They are rocky fragments falling onto the
Earth coming from outer space. We suppose
that the Earth was originated by gathering
many similar rocky fragments and their
composition will help us to infer which
materials is the planet formed of. Many
meteorites content SILICATES, while the
heaviest content IRON and NICKEL

Finally it is most important the study of SEISMIC WAVES
When an earthquake happens
a sequence of seismic waves
is generated, and they spread
throughout inside the planet
deflecting when they collide
with new materials
Waves are recorded in
seismographs at different
stations throughout the world.
The combination of all these
data makes possible to
calculate the waves speed and
trajectory

The analysis of data collected from seismic waves has led to infer that
the outer layer of the planet, the CRUST, reaches some 12-35 km deep.
An intermediate layer, the MANTLE, reaches until 2 900 km deep.
Finally, the CORE reaches the very center of the planet and would be
formed by a liquid OUTER CORE and a solid INNER CORE

The Earth’s layers
1. Look at this scheme:

2. The most reasonable hypothesis is to imagine that the
crust and the mantle are made up of SILICATES, while the
core (with the heaviest materials) is made up of IRON and
NICKEL
3. The main evidences are:
the geothermic gradient: temperature increases with
depth composition and temperature of magma ejected by
volcanoes
the terrestrial magnetic field
meteorites
earthquakes
Obviously we cannot be completely sure that the Earth
inside be like that. Science does not allow us to be totally sure
about anything. But this model of the Earth’s inside is the one
that explains better all evidences accumulated until now

4. No, the Earth has not always been like that. In its early
days, the planet had a very thin and light atmosphere and
temperature was so high that there was no liquid water.
Besides, the arrangement of continents and oceans has
changed a lot along the planet history, as we are going to
explain in next section
5. According to the most acceptable theory today, the Moon
would have been formed by gathering fragments torn off
from the Earth’s surface originated by the impact of a
planetoid. Then it is logical to expect that the Moon’s
composition be similar to that of the Earth’s surface

Plate tectonics
 We known now that most present-day mountains have been a
at the sea floor some million years ago. How can it be that the
planet surface undergoes such drastic changes?
 Since some centuries ago geologists attempt to explain the
formation of mountains and the origin of earthquakes and
volcanoes. At first they thought that these phenomena had
different origins
 When volcanoes (red triangles on next slide map) and
earthquakes (yellow dots) were studied they realized they
were concentrated in particular zones, following certain pattern
lines. That singular distribution could not be a coincidence

Volcanoes and earthquakes
Volcanoes: ⏏ / Earthquakes: 

 At the beginning of 20th century, Alfred L. Wegener observed
that the outlines of Africa and South America fitted like a
puzzle. The most surprising was that there also fitted different
geological structures and fossils older that 150 million years
were the same as well
 Wegener supposed that continents were moving along the
time, a theory that was named as the CONTINENTAL DRIFT.
This idea was received initially with skepticism
Alfred Wegener
(Berlin, 1880-
Greenland, 1930)

Present-day continents were long time ago gathered in one only continent

 During the 1960’s they discovered that rocks at the ocean floor
were much less older that the ones in the continents. They
also discovered some sort of undersea mountain ranges
named as OCEANIC RIFTS
 At the rifts, the oceanic crust is recently formed and there are
lot of earthquakes and volcanic eruptions
 They also discovered oceanic trenches, zones that are much
deeper than the rest of the ocean, parallel to archipelagos or
volcanic ranges, where earthquakes are also frequent
 These discoveries led to formulate the hypothesis that the
ocean floor expands at the rifts, where magna goes up, and
disappears at the oceanic trenches, where it sinks

Mechanism to explain the formation of
oceanic rifts and mountain ranges

 All facts described before are explained by the PLATE
TECTONICS THEORY
 According to this theory, the Earth’s surface is formed by
several solid and rigid plates of LITHOSPHERE including the
crust and the upper part of the mantle
 Under the lithosphere lies the ASTHENOSPHERE, much
more fluid, where higher temperatures produce convection
currents, as we can see at the slide before
 Convection currents drag along the lithospheric plates and
make the plates split in some places (at the oceanic rifts) and
in others they crash and then one plate sinks under the other
until they melt (at the oceanic trenches)
 LITHOSPHERIC PLATES are formed of oceanic crust, which
is heavier, and continental crust, which is lighter. When two
plates crash, the oceanic crust sinks under the
asthenosphere and originates an oceanic trench

 Rubbing between plates produces EARTHQUAKES. The plate
lying up compresses and originates mountain ranges. The
plate that is sinking melts and originates magma that reach the
surface through VOLCANOES
 If the crash happens between two plates with continental crust,
its lower density obstructs the sinking of both plates. Then they
compress, produce earthquakes and originate a big continental
range (Alps, Himalaya, Andes...)
 Once they are formed by this mechanism, the new mountains
suffer the slow process of erosion. Present-day hills, with
rounded shapes, are, actually, old mountains
 Scientific theories must be able to make predictions, what plate
tectonics has accomplished several times. For instance, it has
been noted that both sides of an oceanic rift split between 2
and 10 cm per year, according to what this theory predicts

Plate tectonics
1. Questions 1 and 2 are answered at the picture of
lithospheric plates seen before
3. The Andes range originated because of the crash of Nazca
plate against South-American plate, so that the first one
sunk under the second one
4. The origin of Japan was due to the crash of the Pacific
plate against the Euro-Asiatic plate, so that the first one
sunk under the second one
5. The Himalaya range originated because of the crash of the
Indian plate and the Euro-Asiatic plate

6. As we have seen before, new oceanic crust is created at
the rifts, so both sides of one rift are splitting and separate
some centimeters every year. The rift in the middle of the
Atlantic ocean makes this ocean widen from 5 to 10 cm
per year. So, almost 520 years after Columbus went
across it, the Atlantic ocean has become between 26 and
52 meters wider, approximately

To learn more
 BURNHAM, R, DYER, A. y KANIPE, J. Guía del Cielo Nocturno.
Astronomía. Barcelona: Editorial Blume, 2002
 GRAU, et al. Ciències per al Món Contemporani. Ciència en
context. Barcelona: Editorial Teide, 2008
 SAGAN, Carl. Cosmos. Barcelona: Universitat de Barcelona, 2007
 DIVERSOS AUTORS. La Enciclopedia del Estudiante. Volúmen 10
: Ciencias de la Tierra y del Universo. Madrid: Editorial Santillana-
EL PAÍS, 2005
 RIDPATH, Ian. Oxford Dictionary Of Astronomy. Oxford: Oxford
University Press. 1997

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