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The Earth in the UniverseThe Earth in the Universe

M Barker

Shirebrook Academy

(OCR 21st Century)

20/04/23P1.1 The Earth in the P1.1 The Earth in the UniverseUniverse

20/04/23The eight planets of our Solar The eight planets of our Solar SystemSystem

Mercury

MarsJupiter

Saturn

Neptune

Uranus

VenusEarth

As well as the eight planets, the solar system is also made up of asteroids, dwarf planets, comets and

moons

20/04/23Different OrbitsDifferent Orbits

Mercury

MarsJupiter

Saturn

Neptune

Uranus

Pluto

VenusEarth

Mercury = 88 days

Mars = 687 days

Pluto = 90,500 days

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The Earth’s OrbitThe Earth’s Orbit

Ellipse

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AsteroidsAsteroids

An “asteroid belt” lies between Mars and Jupiter. But what is an asteroid?

20/04/23CometsCometsComets are balls of dust and frozen gas. They have very elliptical orbits:

Notice how the tail always points away from the sun!

20/04/23The Solar System The Solar System summarisedsummarisedWhat makes up our solar system? Complete the following

mind map with what you now about each object:

The solar system

20/04/23Solar systems, galaxies and the Solar systems, galaxies and the UniverseUniverse

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…

Our planet (around 13,000km diameter and 4500 million years old) is pretty 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 systemHow to make a solar system

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Stage 1: NebulaeStage 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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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 2: Throw the nebula Stage 2: Throw the nebula togethertogether

20/04/23Stage 3: Make a starStage 3: Make a star

Any element in space that is heavier than helium is thought to have been made in a star.

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.

Words – heavier, balanced, hydrogen, nuclear, temperatures

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Observing the UniverseObserving the Universe

All of these methods rely on detecting radiation from stars.

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The Light YearThe 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 spaceDistances in space20/04/23

The Sun, our closest star, is 1.6x10-5 light years away from us.

The Andromeda Galaxy (our closest galaxy) – approximately 2.5 million light years away

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.

20/04/23Measuring distance using Measuring distance using brightnessbrightness

The sun looks very bright. But, to be

fair, it’s very close to us so it should look

bright!

20/04/23Measuring distance using Measuring distance using brightnessbrightness

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.

20/04/23Measuring distances to Measuring distances to starsstars

Distant stars

Nearby star

1) Relative BrightnessThe 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.

20/04/23Problems in Measuring Problems in Measuring DistancesDistances

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:

20/04/23How our Earth and the Sun How our Earth and the Sun compare to others… compare to others…

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20/04/23How did the universe How did the universe begin?begin?

Scientists believe that the universe began by a “big bang” around 14 billion years ago:

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Evidence about the Evidence about the origins of the universe…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”.

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After

helium

If the light source is moving away the absorption spectra look a little different…

helium

Before

20/04/23The absorption lines have all been “shifted” towards the longer wavelength end (red end)…

After

Before

A similar effect happens with sound – this is called “The

Doppler Effect”

This is called red shift. The faster the light source moves the further its light will be “shifted”

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Red Shift simplifiedRed Shift simplified

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

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Red shift summaryRed shift summaryLight 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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Hubble’s LawHubble’s Law

Edwin Hubble

1889-1953

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 TheoryBig Bang Theory20/04/23

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.

Stephen Hawking, 1942 -

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 UniverseThe 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 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.

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The End of the UniverseThe End of the Universe

Stephen Hawking

Basically, how the universe will end depends on its “energy-mass

density”.

Siz

e o

f u

niv

ers

e

Time

Open universe

Closed universe

Critical density

Now

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P1.2 The Changing EarthP1.2 The Changing Earth

20/04/23Evidence for the age of the Evidence for the age of the EarthEarth

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.

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Continental DriftContinental DriftLook 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

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Tectonic theoryTectonic 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

20/04/23Another Example of Continental Another Example of Continental DriftDrift

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.

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Tectonic theoryTectonic theoryThe Evidence:

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.

Conclusion – scientists now believe Wegener’s Tectonic Theory

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.

20/04/23Movement of the Movement of the LithosphereLithosphereThe 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

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Sea Floor SpreadingSea Floor Spreading

Oceanic Crust

Mantle

Magma

Earthquakes and volcanic eruptions can be common here

Igneous Rock

Convection Currents

20/04/23Magnetic Patterns in Sea Floor Magnetic Patterns in Sea Floor SpreadingSpreading

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.

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More on Plate MovementsMore on Plate Movements

Convection Currents

Thin, dense oceanic plate

Thick, less dense

continental plate

Subduction

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The Structure of the EarthThe Structure of the EarthA thin crust - 10-100km 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)…

20/04/2320/04/23An introduction to WavesAn introduction to Waves

A Wave is a “movement of energy” but NOT a transfer of matter

20/04/2320/04/23Transverse vs. longitudinal Transverse vs. longitudinal waveswaves

Transverse waves are when the displacement is at right angles to the direction of the wave.

Longitudinal waves are when the displacement is parallel to the direction of the wave…

Dis

pla

cem

en

t

Direction

Direction

Displacement

Examples – light, other EM waves, some seismic waves

Examples – sound, some seismic waves

20/04/2320/04/23Seismic wavesSeismic wavesEarthquakes 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

20/04/2320/04/23Seismic wavesSeismic waves

These P waves travel through the Earth and are refracted when they pass through a medium

These P waves are being reflected at the crust

These S waves cannot travel through the outer core as they only go through solids – this tells us that the outer core is liquid

The paths of these waves are all curved because density is

gradually changing

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Locating EarthquakesLocating Earthquakes

By measuring the time it takes the wave to travel to these locations the location of the earthquake can be found.

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Wave definitions…Wave definitions…

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)

20/04/2320/04/23Distance, Speed Distance, Speed and Time for and Time for

waveswavesSpeed = distance (in metres)

time (in seconds)

D

TS

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 wavesDrawing 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 EquationThe Wave Equation

All E-M waves obey the Wave Equation:

Wave speed (v) = frequency (f) x wavelength ()

in m/s in Hz in m

V

f

Notice that frequency is inversely proportional to

wavelength – if wavelength goes up, frequency goes

down

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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?

Some example wave equation Some example wave equation questionsquestions

0.2m

0.5m

0.6m/s

3x108m/s