P1 - The Earth in the Universe

P1 - The Earth in the Universe

1. Lesson 1: The Solar System and Beyond

   • The Solar System consists of a star (the Sun) and stuff orbiting it
     • Planets
       • Mercury Venus Earth Mars Jupiter Saturn Uranus Neptune
         • Mercury, Venus, Earth and Mars are called INNER PLANETS
         • Jupiter, Saturn, Uranus and Neptune are called OUTER PLANETS
       • Eight planets
         • Pluto is not a planet anymore
       • Orbit in almost circular paths
         • Elipses
     • The asteroid planet comes between the inner and outer planets
       • Asteroids and comets are made from stuff that was left over from the Solar System's formation
         • Asteroids are lumps of rubble an rock
         • 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
     • The Solar System is about 5 thousand million years old
       • Formed over long periods of time from big clouds of dust and gas
         • 1) A cloud started to get squeezed slightly
           • Nearby exploding star
       • 2) Particles got closer together and gravity caused the cloud to collapse on itself
         • At the centre of the collapse a protostar was formed
       • 3) Fusion started when the temperature got high enough
         • Hydrogen particles joined together to make helium
         • Gives out a lot of heat and light which created a star (the Sun)
       • 4) Around the sun, hydrogen, helium and other heavier elements clumped together to make planets
         • Sun and planets are similar ages
       • We know the Solar System is at least 4500 million years old
         • This is because the oldest rocks on Earth are meteorites that crashed into the Earth about 4500 million years ago
   • Stars and Planets are very different
     • Stars are huge, very hot and give out lots of light
     • Planets are a lot smaller and reflect sunlight
   • Our Solar System is in the Milky Way Galaxy
     • There are about 100,000,000,000 in the galaxy
       • They create spiral arms leading out from the centre
         • The Sun is about halfway along one of the arms
     • The distance between each star in the solar system is millions of times greater than the distance between the planets in the Solar System
   • The Universe is made up of millions of galaxies
   • You can measure distances in the Universe by using light years
     • This is the distance that light travels through a vacuum in one year
   • You need to know relative sizes and distances of different stuff in space
     • And some ages
       • Earth - 5000 years
       • Sun - 5000 years
       • Universe - 14,000 years

2. Lesson 2: Looking into Space

   • We can tell a lot about a star by studying the electromagnetic radiation
     • The colour of a star is a good guide to working out its surface temperature
     • There are various methods to work out how far away a star is
       • 1) For 'nearby' stars you can use a parallax
         • Astronomers take pictures of the sky six months apart
           • This is when the Earth is at opposite sides of its orbit
         • A parallax is when something appears to move when you look at it from different places
         • The apparent movement of the star between the two photos
           • Stars further away appear to move less
       • 2) You can also measure its brightness
         • 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
         • 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
   • The Atmosphere and Light Pollution cause some problems though
     • The atmosphere absorbs a lot of light before it can reach us
     • Light pollution makes it hard to see dim objects
       • Light pollution is light thrown upwards from street lamps, etc.
     • This is why scientists put the Hubble telescope into space - where you can't get these problems
   • We see stars and galaxies as they were in the past
     • Electromagnetic radiation travels very fast
       • 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
         • This means we see the Sun as it was 8 minutes ago
     • The nearest star to our star is about 4.2 light years away from us
       • This means the light takes 4.2 years to reach us
         • We see the star as it was 4.2 years ago
     • For other stars, the effect is more extreme
       • The North Star is about 430 light years away, whihc means we see it as it was during the time of William Shakespeare

3. Lesson 3: The Life of the Universe

   • When a galaxy is moving away from us, the wavelength of the light changes and becomes redder
     • This is called red shift
     • By measuring how much the light has been red-shifted you can work out how quickly it is moving away
       • The greater the red shift, the faster it is moving away
     • From observations of different red shifts of different galaxies we know that the more distant the galaxy the faster it moves away from us
       • This proves that the Universe is expanding
   • Th Big Bang Theory
     • All the galaxies seem to be moving apart from a single point
     • According to the theory, all the matter and energy in the Universe must have been compressed in a very small space
       • It then exploded and expanded and the expansion is still going on
     • The age of the Universe can be estimated from the current rate of expansion
       • They think the Big Bang happened about 14 thousand million years ago
         • It is difficult to estimate because it is hard to tell how much the expansion has slowed down
   • The Universe's ultimate fate depends on how fast it's expanding and the total mass there is in it
     • To calculate the speed of expansion, large distances need to be measured
       • Because of the size of the Universe it is hard to accurately measure the distances involved
     • Also need to observe the motion of objects accurately
       • Only assumptions can be made
         • Pollution gets in the way
     • Difficult to measure mass because most of it appears to be invisible
       • Doesn't glow like a star
       • The amount of dark matter in the Universe has not been measured
         • Scientists aren't exactly sure what it is
         • The dark matter will dictate the future of the Universe
     • All the mass is attracted together by gravity
       • The more mass there is, the greater the pull and the greater the slowing down of the Universe's expansion
   • If there is enough mass compared to how fast the galaxies are moving the Universe will eventually stop expanding
     • This will cause it to contract
       • The Big Crunch
   • If there's not enough mass in the Universe to stop the expansion, it could expand forever
     • Universe becoming more and more spread out into eternity

4. Lesson 4: The Changing Earth

   • The Earth has been changing for thousands of millions of years
   • Rocks provide a record of changes to the Earth
     • Erosion
       • The slow wearing away of soil/rock by water flow or wind.
       • Cliffs worn away by the sea
         • The Grand Canyon
     • Making new rock
       • When lava from volcanoes sets, it forms new rock
     • Fossils
       • Rocks built up around dead animals and plants
     • The oldest rocks found on Earth so far are about 4 thousand million years old
   • The rock cycle
     • 1) Particles eroded from existing rock get washed into the sea and settle as sediment
       • These sediments are crushed together to make sedimentary rocks
     • 2) These can get pushed to the surface or they can descend into the heat and pressure inside the Earth
       • If they descend, the structure of the rock can completely change as it gets heated and crushed
         • Sometimes the rock actually melts and will solidify into new rock on the Earth's surface
     • 3) When any of these rocks are pushed up to the surface, the cycle starts again
       • They gradually get worn down and carried off to the sea again and so on
     • 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.
       • For example, some rock formations show rock that's been squeezed so hard it's just folded

5. Lesson 5: Wegener's Theory of Continental Drift

   • Past beliefs
     • For years, fossils of very similar plants and animals had been found on continents at opposite ends of the Atlantic Ocean
       • 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
     • Why the coastlines of South America and Africa matched so well was also unknown
     • People also didn't understand why fossils of sea creatures had been found in the Alps
   • Alfred Wegener hypothesised that Africa and South America had previously been one continent which had then split
     • He found evidence to back up his hypothesis
       • There were matching layers in the rocks on different continents
       • There were similar fossils in both South America and South Africa
       • His theory of continental drift supposed that 300 million years ago there had been just one supercontintent which he called Pangaea
         • According to Wegener, Pangaea broke into smaller chunks which are our continents which are still slowly drifting apart
     • A lot of people opposed his theory because it opposed things said in the land-bridge theory
       • These were things like mountains being formed as continents crashed into one another
       • Scientist's reactions were hostile
         • 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
         • It also didn't help that Wegener was a meteorologist not a 'proper' geologist, which was frowned upon
   • New evidence
     • In the 1950's, scientists discovered the Mid-Atlantic ridge, which runs the whole length of the Atlantic
       • The found evidence that magma rises up through the sea floor, solidifies and forms underwater mountains that are roughly symmetrical
         • This suggested that the sea floor spread by a few centimetres per year
     • Evidence that the continents are moving apart came from the magnetic orientation of the rocks
       • 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
         • 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
     • This was convincing evidence of how the sea floor was created and how the continents were moved apart

6. Lesson 6: The Structure of the Earth

   • The Earth is almost spherical and has layers
     • The Crust
       • We live on it
       • 20 km thick
       • Continental crust
         • Forms the land
       • Oceanic crust
         • Under oceans
     • The Mantle
       • Properties of solid
       • Flows slowly
     • The Outer Core
       • Hot
       • Radioactive decay
       • Heat and decay cause mantle to flow in convection currents
       • Liquid
     • The Inner Core
       • Solid
       • Made of mainly iron and nickel
   • Tectonic plates
     • Crust and upper mantle
     • Floating

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