The Earth in the Universe

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The Earth in the Universe
(OCR 21st Century)
M Barker Shirebrook Academy
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P1.1 The Earth in the Universe
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The eight planets of our Solar System
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
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Different Orbits
Mercury 88 days
Mercury
Venus
Mars 687 days
Earth
Mars
Pluto 90,500 days
Jupiter
Saturn
Uranus
Neptune
Pluto
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The Earths Orbit
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Asteroids
An asteroid belt lies between Mars and Jupiter.
But what is an asteroid?
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Comets
Comets are balls of dust and frozen gas. They
have very elliptical orbits
Notice how the tail always points away from the
sun!
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The Solar System summarised
What makes up our solar system? Complete the
following mind map with what you now about each
object
The solar system
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Solar systems, galaxies and the Universe
OUR SUN (100 times wider and 4.6 billion years
old), which is small compared to
THE MILKY WAY, which contains at least 200
billion stars and is 100,000 light years across,
which is small compared to
THE UNIVERSE, which contains billions of galaxies
and is 14,000 million years old.
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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
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Stage 2 Throw the nebula together
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Stage 3 Make a star
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Observing the Universe
All of these methods rely on detecting radiation
from stars.
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The Light Year
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.
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Distances in space
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Measuring distance using brightness
The sun looks very bright. But, to be fair, its
very close to us so it should look bright!
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Measuring distance using brightness
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.
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Measuring distances to stars
2) Parallax Parallax is the apparent change in
position of closer stars due to the Earth moving
around the sun.
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Problems in Measuring Distances
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
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How our Earth and the Sun compare to others
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How did the universe begin?
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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If you pass the light through a gas something
different is seen
Some wavelengths of light are absorbed by the gas
an absorption spectrum.
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If the light source is moving away the absorption
spectra look a little different
helium
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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
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 Ill look
slightly more blue. Then, if I walk away from
you, Ill look slightly more red!! Lets 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.
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Red shift summary
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
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Hubbles Law
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.
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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!
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The end of the Universe
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 isnt 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.
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The End of the Universe
Basically, how the universe will end depends on
its energy-mass density.
Open universe
Critical density
Closed universe
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P1.2 The Changing Earth
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Evidence for the age of the Earth
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 Earths age must be older than the oldest
rocks, which are around 4,000,000,000 years old.
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Continental Drift
Look at the coastlines of South America and
Africa. I wonder of they used to fit together
Alfred Wegener
Im going to call this my Theory of Continental
Drift
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Tectonic theory

• Whats my evidence for this? Three things
• The jigsaw fit
• Each continent has similar rocks and fossils
• 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
If it wasnt for processes like this then, if you
think about it, continents would eventually
disappear due to erosion. Fascinating.
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Tectonic theory

• The Evidence
• Some continents look like they used to fit
  together
• 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 wasnt 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 Wegeners
Tectonic Theory
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Movement of the Lithosphere
The Earths LITHOSPHERE (i.e. the _______) is
split up into different sections called ________
plates
Words earthquakes, crust, apart, tectonic, year
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Sea Floor Spreading
Magma
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Magnetic Patterns in Sea Floor Spreading
The Earths 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.
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More on Plate Movements
Thick, less dense continental plate
Thin, dense oceanic plate
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The Structure of the Earth
How do we know? A lot of the evidence for these
facts comes from studying earthquakes (seismic
waves)
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An introduction to Waves
A Wave is a movement of energy but NOT a
transfer of matter
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Transverse vs. longitudinal waves
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Transverse waves are when the displacement is at
right angles to the direction of the wave.
Examples light, other EM waves, some seismic
waves
Longitudinal waves are when the displacement is
parallel to the direction of the wave
Examples sound, some seismic waves
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Seismic waves
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Earthquakes travel as waves through the Earth
we call them SEISMIC WAVES. There are two types

• P waves
• They are longitudinal so they cause the ground to
  move up and down
• They can pass through solids and liquids
• They go faster through more dense material

• S waves
• They are transverse so they cause the ground to
  move from right to left
• They ONLY pass through solids
• They are slower than P waves
• They go faster through more dense material

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Seismic waves
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The paths of these waves are all curved because
density is gradually changing
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Locating Earthquakes
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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)
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Distance, Speed and Time for waves
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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?

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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
in m
Notice that frequency is inversely proportional
to wavelength if wavelength goes up, frequency
goes down
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Some example wave equation questions
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1. A water wave has a frequency of 2Hz and a
   wavelength of 0.3m. How fast is it moving?
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?
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?
4. Purple light has a wavelength of around 6x10-7m
   and a frequency of 5x1014Hz. What is the speed
   of purple light?

0.6m/s
0.2m
0.5m
3x108m/s