P1 - The Earth in the Universe

Lesson 1: The Solar System and Beyond
1. The Solar System consists of a star (the Sun) and stuff orbiting it
  1. Planets
    1. Mercury Venus Earth Mars Jupiter Saturn Uranus Neptune
      1. Mercury, Venus, Earth and Mars are called INNER PLANETS
      2. Jupiter, Saturn, Uranus and Neptune are called OUTER PLANETS
    2. Eight planets
      1. Pluto is not a planet anymore
    3. Orbit in almost circular paths
      1. Elipses
  2. The asteroid planet comes between the inner and outer planets
    1. Asteroids and comets are made from stuff that was left over from the Solar System's formation
      1. Asteroids are lumps of rubble an rock
      2. Comets are balls of rock, dust and ice
        Orbit the sun in very long elipses
        The sun is at the end of the elipses
        When a comet approaches the sun, the ice melts leaving a tail of gas and debris
  3. The Solar System is about 5 thousand million years old
    1. Formed over long periods of time from big clouds of dust and gas
      1. 1) A cloud started to get squeezed slightly
        Nearby exploding star
    2. 2) Particles got closer together and gravity caused the cloud to collapse on itself
      1. At the centre of the collapse a protostar was formed
    3. 3) Fusion started when the temperature got high enough
      1. Hydrogen particles joined together to make helium
      2. Gives out a lot of heat and light which created a star (the Sun)
    4. 4) Around the sun, hydrogen, helium and other heavier elements clumped together to make planets
      1. Sun and planets are similar ages
    5. We know the Solar System is at least 4500 million years old
      1. This is because the oldest rocks on Earth are meteorites that crashed into the Earth about 4500 million years ago
2. Stars and Planets are very different
  1. Stars are huge, very hot and give out lots of light
  2. Planets are a lot smaller and reflect sunlight
3. Our Solar System is in the Milky Way Galaxy
  1. There are about 100,000,000,000 in the galaxy
    1. They create spiral arms leading out from the centre
      1. The Sun is about halfway along one of the arms
  2. The distance between each star in the solar system is millions of times greater than the distance between the planets in the Solar System
4. The Universe is made up of millions of galaxies
5. You can measure distances in the Universe by using light years
  1. This is the distance that light travels through a vacuum in one year
6. You need to know relative sizes and distances of different stuff in space
  1. And some ages
    1. Earth - 5000 years
    2. Sun - 5000 years
    3. Universe - 14,000 years
Lesson 2: Looking into Space
1. We can tell a lot about a star by studying the electromagnetic radiation
  1. The colour of a star is a good guide to working out its surface temperature
  2. There are various methods to work out how far away a star is
    1. 1) For 'nearby' stars you can use a parallax
      1. Astronomers take pictures of the sky six months apart
        This is when the Earth is at opposite sides of its orbit
      2. A parallax is when something appears to move when you look at it from different places
      3. The apparent movement of the star between the two photos
        Stars further away appear to move less
    2. 2) You can also measure its brightness
      1. Unfortunately a star that looks very bright from Earth could either be
        a) Quite close to Earth but not actually that bright
        b) Or a long way away and very bright
      2. Astronomers know how much radiation certain types of star actually emit, though, so by examining the brightness, they can tell how far from Earth it is
2. The Atmosphere and Light Pollution cause some problems though
  1. The atmosphere absorbs a lot of light before it can reach us
  2. Light pollution makes it hard to see dim objects
    1. Light pollution is light thrown upwards from street lamps, etc.
  3. This is why scientists put the Hubble telescope into space - where you can't get these problems
3. We see stars and galaxies as they were in the past
  1. Electromagnetic radiation travels very fast
    1. The Sun is about 150 million km away from Earth so the radiation from the Sun reaches us 8 minutes after it has left the Sun
      1. This means we see the Sun as it was 8 minutes ago
  2. The nearest star to our star is about 4.2 light years away from us
    1. This means the light takes 4.2 years to reach us
      1. We see the star as it was 4.2 years ago
  3. For other stars, the effect is more extreme
    1. The North Star is about 430 light years away, whihc means we see it as it was during the time of William Shakespeare
Lesson 3: The Life of the Universe
1. When a galaxy is moving away from us, the wavelength of the light changes and becomes redder
  1. This is called red shift
  2. By measuring how much the light has been red-shifted you can work out how quickly it is moving away
    1. The greater the red shift, the faster it is moving away
  3. From observations of different red shifts of different galaxies we know that the more distant the galaxy the faster it moves away from us
    1. This proves that the Universe is expanding
2. Th Big Bang Theory
  1. All the galaxies seem to be moving apart from a single point
  2. According to the theory, all the matter and energy in the Universe must have been compressed in a very small space
    1. It then exploded and expanded and the expansion is still going on
  3. The age of the Universe can be estimated from the current rate of expansion
    1. They think the Big Bang happened about 14 thousand million years ago
      1. It is difficult to estimate because it is hard to tell how much the expansion has slowed down
3. The Universe's ultimate fate depends on how fast it's expanding and the total mass there is in it
  1. To calculate the speed of expansion, large distances need to be measured
    1. Because of the size of the Universe it is hard to accurately measure the distances involved
  2. Also need to observe the motion of objects accurately
    1. Only assumptions can be made
      1. Pollution gets in the way
  3. Difficult to measure mass because most of it appears to be invisible
    1. Doesn't glow like a star
    2. The amount of dark matter in the Universe has not been measured
      1. Scientists aren't exactly sure what it is
      2. The dark matter will dictate the future of the Universe
  4. All the mass is attracted together by gravity
    1. The more mass there is, the greater the pull and the greater the slowing down of the Universe's expansion
4. If there is enough mass compared to how fast the galaxies are moving the Universe will eventually stop expanding
  1. This will cause it to contract
    1. The Big Crunch
5. If there's not enough mass in the Universe to stop the expansion, it could expand forever
  1. Universe becoming more and more spread out into eternity
Lesson 4: The Changing Earth
1. The Earth has been changing for thousands of millions of years
2. Rocks provide a record of changes to the Earth
  1. Erosion
    1. The slow wearing away of soil/rock by water flow or wind.
    2. Cliffs worn away by the sea
      1. The Grand Canyon
  2. Making new rock
    1. When lava from volcanoes sets, it forms new rock
  3. Fossils
    1. Rocks built up around dead animals and plants
  4. The oldest rocks found on Earth so far are about 4 thousand million years old
3. The rock cycle
  1. 1) Particles eroded from existing rock get washed into the sea and settle as sediment
    1. These sediments are crushed together to make sedimentary rocks
  2. 2) These can get pushed to the surface or they can descend into the heat and pressure inside the Earth
    1. If they descend, the structure of the rock can completely change as it gets heated and crushed
      1. Sometimes the rock actually melts and will solidify into new rock on the Earth's surface
  3. 3) When any of these rocks are pushed up to the surface, the cycle starts again
    1. They gradually get worn down and carried off to the sea again and so on
  4. The rock cycle needs dome very powerful forces to push rock up or down as described - but there's very good evidence that this is what happens.
    1. For example, some rock formations show rock that's been squeezed so hard it's just folded
Lesson 5: Wegener's Theory of Continental Drift
1. Past beliefs
  1. For years, fossils of very similar plants and animals had been found on continents at opposite ends of the Atlantic Ocean
    1. People thought this was because the continents had been linked by land-bridges which had sunk or been covered in water as the Earth cooled
  2. Why the coastlines of South America and Africa matched so well was also unknown
  3. People also didn't understand why fossils of sea creatures had been found in the Alps
2. Alfred Wegener hypothesised that Africa and South America had previously been one continent which had then split
  1. He found evidence to back up his hypothesis
    1. There were matching layers in the rocks on different continents
    2. There were similar fossils in both South America and South Africa
    3. His theory of continental drift supposed that 300 million years ago there had been just one supercontintent which he called Pangaea
      1. According to Wegener, Pangaea broke into smaller chunks which are our continents which are still slowly drifting apart
  2. A lot of people opposed his theory because it opposed things said in the land-bridge theory
    1. These were things like mountains being formed as continents crashed into one another
    2. Scientist's reactions were hostile
      1. Wegener's explanation of how the drifting was happening wasn't convincing enough because the movement wasn't detectable
        Wegener suggested that tidal movement or the Earth's rotation could cause the drifting
        Geologists showed this was impossible
      2. It also didn't help that Wegener was a meteorologist not a 'proper' geologist, which was frowned upon
3. New evidence
  1. In the 1950's, scientists discovered the Mid-Atlantic ridge, which runs the whole length of the Atlantic
    1. The found evidence that magma rises up through the sea floor, solidifies and forms underwater mountains that are roughly symmetrical
      1. This suggested that the sea floor spread by a few centimetres per year
  2. Evidence that the continents are moving apart came from the magnetic orientation of the rocks
    1. As liquid magma erupts out of the gap, iron particles align themselves with the Earth's magnetic field and as it cools, they set in position
      1. Every half a million years, the Earth's magnetic orientation swaps direction and the rocks on either side of the ridge has bands of alternate magenetic polarity, syymetrical about the ridge
  3. This was convincing evidence of how the sea floor was created and how the continents were moved apart
Lesson 6: The Structure of the Earth
1. The Earth is almost spherical and has layers
  1. The Crust
    1. We live on it
    2. 20 km thick
    3. Continental crust
      1. Forms the land
    4. Oceanic crust
      1. Under oceans
  2. The Mantle
    1. Properties of solid
    2. Flows slowly
  3. The Outer Core
    1. Hot
    2. Radioactive decay
    3. Heat and decay cause mantle to flow in convection currents
    4. Liquid
  4. The Inner Core
    1. Solid
    2. Made of mainly iron and nickel
2. Tectonic plates
  1. Crust and upper mantle
  2. Floating

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