Human species in the

Universe1. 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

1. The Universe & the Earth

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

Ptolemy Geocentric Model

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)

Sputnik (USSR 1957)

Neil Armstrong

(USA 1969)

International Space Station

(1998)

The discovery of new

planetoids1. 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

Exo-planets

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?

Milky Way

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) cluster1. 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

21H + 31H 4

2He + 10n

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?

Is the Sun

round?

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

Crab Nebula

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

Black hole at Cygnus X-1Black hole in the middle of a cluster

Component of a binary system

transformed into a black hole

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 layers1. 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

Continents and oceanic rifts

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

Lithospheric plates

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 tectonics1. 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