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The Earth in the Universe
(OCR 21st Century)
W Richards
The Weald School
P1.1 The Earth in the Universe
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The eight planets of our Solar System
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Mercury
Venus
Earth
Mars
Jupiter
Saturn
Uranus
Neptune
As well as the eight planets, the solar system is also made
up of asteroids, dwarf planets, comets and moons
Different Orbits
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Mercury = 88 days
Mercury
Venus
Earth
Mars
Mars = 687 days
Pluto =
Jupiter
90,500 days
Saturn
Uranus
Neptune
Pluto
The Earth’s Orbit
Ellipse
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Asteroids
An “asteroid belt” lies between Mars and
Jupiter. But what is an asteroid?
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Comets
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Comets are balls of dust and frozen
gas. They have very elliptical orbits:
Notice how the tail always points away from the sun!
The Solar System summarised
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What makes up our solar system? Complete the following mind
map with what you now about each object:
The solar system
Solar systems, galaxies and the Universe
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Our planet (around 13,000km diameter and 4500 million
years old) is pretty small compared to...
OUR SUN (100 times wider
and 4.6 billion years old),
which is small compared to…
THE UNIVERSE, which
contains billions of galaxies and
is 14,000 million years old.
THE MILKY WAY, which
contains at least 200 billion
stars and is 100,000 light
years across, which is small
compared to…
How to make a solar system
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Stage 1: Nebulae
A nebulae is a collection of dust, gas and rock.
Some examples of nebulae…
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Dark nebula
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Emission nebula
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Planetary nebula
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Reflection nebula
Stage 2: Throw the nebula together
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Gravity will slowly pull these
particles together…
As they move inwards their
gravitational potential energy
is converted into heat and a
big object (PROTOSTAR) or
smaller objects (planets,
asteroids etc) are formed
Stage 3: Make a star
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In a star the forces of
gravitational attraction
pulling the particles inwards
are _________ by forces
acting outwards due to the
huge __________ inside the
star.
Stars are basically ________ reactors that use _______
as a fuel. During its main sequence a star will release
energy by combining hydrogen and helium nuclei (light
elements) into _________ elements.
Any element in space that is heavier than helium is
thought to have been made in a star.
Words – heavier, balanced, hydrogen, nuclear, temperatures
Observing the Universe
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All of these methods rely on detecting radiation from stars.
The Light Year
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Distances in space are so big that they are measured in units
called “light years”:
1 light year = the distance
travelled by light in one yar
Q. If light travels through space (i.e. A vacuum) at 300,000
km/s how far is one light year?
Because of this, when we see stars in the night sky we are
actually seeing them as they were in the past.
Distances in space
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The Sun, our closest star, is 1.6x10-5 light years
away from us.
The next closest star, Proxima
Centauri (4.2 light years away)
The centre of our galaxy, the Milky Way, is
around 26,000 light years away.
The Andromeda Galaxy (our closest galaxy)
– approximately 2.5 million light years away
Measuring distance using brightness
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The sun looks very
bright. But, to be fair,
it’s very close to us so it
should look bright!
Measuring distance using brightness
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When I look at these stars some appear brighter than
others. This because they are either brighter stars or
closer to me.
For example, the star Antares is 10,000 times brighter
than the sun but it is 500 light years away from me, so it
is only the 15th brightest star in the night sky.
Measuring distances to stars
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1) Relative Brightness
The further away a
star is the dimmer it
is. Simple.
2) Parallax
Parallax is the
apparent change in
position of closer
stars due to the
Earth moving around
the sun.
Distant
stars
Nearby star
Problems in Measuring Distances
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1) Light pollution and other
atmospheric conditions can
interfere with observing stars:
2) Stars are simply very far away so the
angles involved in using techniques like
parallax are very small:
How our Earth and the Sun
compare to others…
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How did the universe begin?
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Scientists believe that the universe began by a “big bang”
around 14 billion years ago:
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Evidence about the origins of
the universe…
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Source of
light
“Spectra”
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If you pass the light through a gas something
different is seen…
helium
Some wavelengths of light
are absorbed by the gas –
an “absorption spectrum”.
If the light source is moving away the absorption
spectra look a little different…
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Before
helium
helium
After
The absorption lines have all been “shifted”
towards the longer wavelength end (red end)…
This is called red
shift. The faster
the light source
moves the further
its light will be
“shifted”
Before
After
A similar effect happens with sound –
this is called “The Doppler Effect”
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Red Shift simplified
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Basically, if I walk towards you I’ll look
slightly more blue. Then, if I walk away
from you, I’ll look slightly more red!!
Let’s try it…
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Light from different stars and from the edge
of the universe also shows this “red-shift”.
This suggests that everything in the universe
is moving away from a single point.
This is the BIG
BANG theory
Red shift summary
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Light from other galaxies has a longer _________ than
expected. This shows that these galaxies are moving ____
from us very quickly. This effect is seen to a greater
extent in galaxies that are _______ away from us. This
indicates that the further away the galaxy is, the ______
it is moving.
This evidence seems to suggest that everything in the
universe is moving away from a single point, and that this
process started around 15 _____ years ago. This is the
____ ________ Theory.
Words to use – faster, away, big bang,
billion, wavelength, further
Hubble’s Law
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The speed at which galaxies are
moving away from us is proportional
to their distance from us.
In other words, the further away
they are, the faster they go.
Edwin Hubble
1889-1953
Big Bang Theory
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Some scientists have explained that red shift can actually be used to
support the Big Bang Theory – this explanation is based around the rates
of expansion and contraction of different galaxies. If our neighbouring
galaxy is expanding at a different rate to the Milky Way then it will appear
red or blue-shifted.
So Mr President, red shift
shows us that galaxies are
moving and therefore we
assume that space itself is
expanding. Elementary!
Stephen Hawking, 1942 -
The end of the Universe
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There are some theories about how the
universe will end but its difficult to tell due
to difficulties in measuring objects that are
so far away:
“The big crunch” – if there is too much mass (i.e. too much
matter) the universe will collapse under its own gravity. It
may then do another “big bang” – this is the “oscillating
universe” theory.
“Expanding Universe” – if there isn’t enough mass in the
universe then it will just keep on expending forever.
If there is just the right mass in the universe then it will
reach a fixed size.
The End of the Universe
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Basically, how the universe will end
depends on its “energy-mass density”.
Size of universe
Stephen Hawking
Now
Open universe
Critical
density
Closed
universe
Time
P1.2 The Changing Earth
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Evidence for the age of the Earth
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Scientists once thought that the Earth was only 6000 years
old. Rocks have provided lots of evidence for the world being
older.
1) Erosion
2) Craters
3) Mountains
4) Fossils
5) Folding
6) Radioactive dating
The Earth’s age must be older than the oldest rocks, which are
around 4,000,000,000 years old.
Continental Drift
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Look at the coastlines of South
America and Africa. I wonder of they
used to fit together…
Alfred
Wegener
I’m going to call this my
Theory of Continental Drift
Tectonic theory
What’s my evidence for this? Three things:
1) The “jigsaw fit”
2) Each continent has similar rocks and fossils
3) Each continent has similar animal species
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Another Example of Continental Drift
The formation of mountain ranges can be explained by tectonic
theory. Consider the Himalayas at the top of India:
This is where
India is now
This is where
India was millions
of years ago
If it wasn’t for processes like this then, if you think
about it, continents would eventually disappear due to
erosion. Fascinating.
The Evidence:
Tectonic theory
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1) Some continents look like they used to “fit”
together
2) Similar rock patterns and fossil records
The Problems:
Wegener couldn't explain how continental drift
happened or provide evidence so nobody
believed him. Also, he wasn’t a geologist so he
had no credibility and there were other
explanations for the same evidence.
The Answer:
Scientists discovered 50 years later that the Earth generates massive
amounts of heat through radioactive decay in the core. This heat
generated convection currents in the mantle causing the crust to move.
Conclusion – scientists now believe Wegener’s Tectonic Theory
Movement of the Lithosphere
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The Earth’s LITHOSPHERE (i.e. the _______) is split
up into different sections called ________ plates:
These plates are moving ______ from each other a few
centimetres every _______. They can slide past each
other, move apart from each other or move towards
each other, causing volcanoes and _________.
Words – earthquakes, crust, apart, tectonic, year
Sea Floor Spreading
Earthquakes and
volcanic eruptions can
be common here
Igneous Rock
Oceanic Crust
Mantle
Convection
Currents
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Magma
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Magnetic Patterns in Sea Floor Spreading
The Earth’s magnetic field swaps poles every million years.
The above picture shows those changes recorded over time in
rocks on the sea floor and provides evidence for long-term sea
floor spreading.
More on Plate Movements
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Subduction
Thin, dense oceanic plate
Convection
Currents
Thick, less dense
continental plate
The Structure of the Earth
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A thin crust - 10100km thick and
not very dense
A mantle – extends
almost halfway to the
centre, hot and dense
A core – made of molten
nickel and iron. Outer
part is liquid and inner
part is solid. Gets hot
due to radioactive decay.
How do we know? A lot of the evidence for these facts
comes from studying earthquakes (seismic waves)…
An introduction to Waves
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A Wave is a “movement of energy” but NOT a transfer of
matter
Transverse vs. longitudinal waves
Transverse waves
are when the
displacement is at
right angles to the
direction of the
wave.
Displacement
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Direction
Examples – light, other EM waves, some seismic waves
Displacement
Direction
Longitudinal waves
are when the
displacement is
parallel to the
direction of the
wave…
Examples – sound, some seismic waves
Seismic waves
Earthquakes travel as waves through the Earth – we call them
SEISMIC WAVES. There are two types:
P waves:
1) They are longitudinal so they cause the ground
to move up and down
2) They can pass through solids and liquids
3) They go faster through more dense material
S waves:
1) They are transverse so they cause the ground
to move from right to left
2) They ONLY pass through solids
3) They are slower than P waves
4) They go faster through more dense material
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Seismic waves
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These P waves are
being reflected at the
crust
These P waves travel
through the Earth and
are refracted when
they pass through a
medium
The paths of these waves are all
curved because density is
gradually changing
These S waves cannot
travel through the
outer core as they only
go through solids – this
tells us that the outer
core is liquid
Locating Earthquakes
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By measuring the time
it takes the wave to
travel to these
locations the location
of the earthquake can
be found.
Wave definitions…
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1) Amplitude – this is
“how high” the wave
is:
2) Wavelength () – this is the
distance between two
corresponding points on the
wave and is measured in metres:
3) Frequency – this is how many waves pass by
every second and is measured in Hertz (Hz)
4) Speed – this is how fast the wave travels and is
measured in metres per second (m/s)
Distance, Speed
and Time for waves
Speed = distance (in metres)
time (in seconds)
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D
S
T
1) A water wave travels 200 metres in 40 seconds. What is its speed?
2) Another wave covers 2km in 1,000 seconds. What is its speed?
3) Sound travels at around 330m/s. How long does it take to travel one
mile (roughly 1,600m)?
4) Light travels at a speed of 300,000,000m/s. How long would it take to
travel around the world if the diameter at the equator is around
40,000km?
Drawing waves
1) Low amplitude, low frequency:
2) Low amplitude, high frequency:
3) High amplitude, low frequency:
4) High amplitude, high frequency:
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The Wave Equation
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All E-M waves obey the Wave Equation:
Wave speed (v) = frequency (f) x wavelength ()
in m/s
in Hz
Notice that frequency is
inversely proportional to
wavelength – if wavelength
goes up, frequency goes down
V
f
in m

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Some example wave equation questions
1) A water wave has a frequency of 2Hz and a wavelength
of 0.3m. How fast is it moving?
0.6m/s
2) A water wave travels through a pond with a speed of
1m/s and a frequency of 5Hz. What is the wavelength
of the waves?
0.2m
3) The speed of sound is 330m/s (in air). When Dave
hears this sound his ear vibrates 660 times a second.
What was the wavelength of the sound?
0.5m
4) Purple light has a wavelength of around 6x10-7m and a
frequency of 5x1014Hz. What is the speed of purple
light?
3x108m/s