- The solar system was formed over a very long period of time,about 5000 million years ago.
- Solar system started as clouds of dust and gas,which were pulled together by the force of gravity.
- This created intense heat.Eventually nuclear fusion began to take place and a star was born-The Sun.
- The remaining dust and gasses formed smaller masses,which were attracted to the Sun.
- The smaller masses are:-
- Planets-8 large masses that move around the Sun.
- Moons-small masses that orbit the planets.
- Asteroids-small,icy masses that orbit the Sun.
- Dwarf planets-small spherical objects that have not cleared their orbits of other objects.
- Planets,moons and asteroids all move in elliptical orbits.Comets move in highly elliptical orbits.
- It takes Earth 1 year to orbit around the Sun.
The Sun&The Universe
- Suns energy(heat and light)comes from nuclear fusion.Hydrogen and nuclei fuse together to produce a larger mass.
- Duing fusion,some of energy trapped inside hydrogen nuclei is released.
- All the chemical elements with a larger mass than helium were formed by nuclear fusion in earlier stars.
- Universe is much older than Sun and Earth;approximately 14000 million years old.
The Speed of Light
- Light travels at very high but limited speeds-meaning that if the distance to an object is long enough ,the time taken for light to get there can be measured.
- Speed of light is 300 000km/s in a vacuum.
- Light takes just over a second to reach the moon.
- Light from Sun takes 8 minutes to reach Earth.This means if we look at the sun we are actually seeing what it looked like 8 minutes before.
- Vast distances are measured in light years.
- 1 light year is the distance light travels in a year-9500 billion km.
- The nearest galaxy to the milky way is 2.2 million light years away.
Measuring distances in Space
- Astronomers work out distances to different stars using two different methods:
- Relative Brightness-In general ,the dimmer a star,the further away it is.However,stars can vary in brightness so we cant be 100% certain.
- Parallax-If you hold a finger at arm's length and close each eye in turn,the finger appears to move.The closer the finger is to your face the more it appears to move.Parallax uses this idea to work out distances.As the Earth orbits the Sun,stars in the near distance appear to move against the background of very distant stars.The closer they are ,the more they appear to move.The position of a star is measured at six monthly intervals.These measurements can be used to calculate its distance from Earth.However, the further away the star is,the more difficult it is to determine an accurate measurement.
Distant Stars&Other Galaxies
- Because stars are so far away ,everything we know about them is worked out from the radiation they produce:visible light,ultraviolet and infrared.
- All our electric lights on Earth illuminate the night sky,so it is very difficult to see the stars sometimes.This is called light pollution.
- In 1990,the Hubble Space Telescope was launched.It orbits the Earth at a height of 600km,so it is not affected by light pollution or atmospherivc conditions.
- If a source of light is moving away from us,the wavelengths of the light are longer than they would be if the source was stationary.
- The wavelengths of light from almost all galaxies are longer than scientists would expect.This means that the galaxies are moving away from us.
Edwin Hubble-Hubble Law
- In 1929,Edwin Hubble discovered that light from distant galaxies had even longer wavelengths.Therefore they must be moving away from us faster.As a result,he developed the Hubble Law:
The speed at which galaxies are moving away from us is proportional to their distance from us-the faster a galaxy a moving ,the further away it is.
- If all the galaxies are moving away from one another,this must mean that space is expanding.
- If a wave source is moving away from or towards an observer,there will be a change in the observed wavelength and frequency.
- If a source of light moves away from an observer,the wavelengths of the light in its spectrum are longer than if it was not moving.
- This is known as redshift because the wavelengths 'shift' towards tyhe red end of the spectrum.
- All distant galaxies appear to be 'redshifted' ,which means they are moving away from us.
The Beginning&The End
- THE BEGINNING
- When scientists trace the path of galaxies,they all appear to be moving away from the same point.
- There have been many theories about how the Universe began.The one that best explains this evidence is The Big Bang Theory,which says the Universe started with a huge explosion 14000 million years ago.
- It is difficult to predict the fate of the Universe because it is very hard to measure because it is very hard to measure the very large distances involved,It is also very difficult to study the motion of very distant objects.
- The future depends on the amount of mass in the Universe.If there is not enough mass,the universe will not keep expanding.If there is not enough mass,gravity will pull everything back together and the Universe will collapse with a big crunch.Measuring the amount of mass in the Universe is very difficult,so its ultimate fate is hard to predict.
- People once thought the Earth was only 6000 years old.There was no way of testing this theory,so people believed it for a long time.
- We know that rocks provide evidence of how the Earth has changed and clues as to its age.
- Erosion-the Earth's surface is made up of layers of rock,one on top of the other ,with the oldest at the bottom.The layers are made of compacted sediment,which is produced by weathering and erosion.Erosion changes the surface of the planet over long periods of time.
- Craters-the surface of the Moon is covered with impact craters from collisions with meteors.However,the Earth which is much larger has had fewer collision ,due to the Earth's atmosphere,but craters have also been erased by erosion.
- Mountain Formation-if new mountains were not being formed,the whole Earth would of been eroded down to sea level.
- Fossils-plants and animals trapped in layers of sedimentary rock have formed fossils,providing evidence of how Earth has changed over millions of years.
- Folding-some rocks look like they have been folded like plastercine.This would require a big force to be applied over a long period of time-further evidence that the Earth is very old.
- Radioactive Dating-all rocks are radioactive,but the amount of radiation they emit decreases over time-Radioactive dating measures radiation level to find out how old they are.
The Structure of the Earth
Thin rocky crust
- Its thickness varies between 10km and 100km.
- Oceanic crust lies beneath the oceans.
- Continental crust forms continents.
- Extends almost halfway to the centre.
- Has a higher density,and a different composition,than rock in the crust.
- Very hot,but under pressure.
- Made of nickel&iron.
- Over half of Earths radius;liquid outer part&solid inner part.
- Decay of radioactive elements inside the Earth releases energy,keeps Earths interior hot.
- Alfred Wegner(1880-1930)was a meteorologist who put forward a theory called continental drift.
- He saw that continents fit together like a jigsaw,with mountain ranges and sedimentary rock patterns matching up perfectly.
- Fossils of same land animals on different continents.
- Wegner proposed that the different continents were once joined but got seperated and drifted apart.
- Also claimed that when 2 continents collided,they forced each other upwards to make mountains.
- Ideas not accepted because:-
- he was not a geologist so considered an outsider.
- big idea-little evidence.
- evidence could be explained simply by land bridge connecting continents sunk or eroded.
- Earth's crust is cracked into several large pieces known as tectonic plates.
- Plates float on Earth's mantle-because they are less dense.
- They can move apart,towards each other or slide past each other.
- Lines where plates meet are called plate boundaries.
- These are where volcanoes,earthquakes and mountain building occur.
- Earhquakes near sea are called tsunami's.
- Movement of the tectonic plates can happen suddenly due to a build up in pressure and can have disastrous consequences.
- Move in three ways;
- Sliding past each other-When plates slide past each other ,huge stresses and strains build up in the crust,which eventually have to be released in order for movement to occur.Release of energy is called an earthquake.
Tectonic Plates cont..
- Move away from each other-constructive plate boundaries-When plates move away from each other at an oceanic ridge,fractures occur.Molten rock rises to surface,where it solidifies to form new ocean floor-known as seafloor spreading.Because new rock is being formed ,these are called constructive plate boundaries.
- Move towards each other-Destructive plate boundaries-As plates are moving away from each other in some places,it follows that they must be moving towards each other in other places.When plates collide,one is forced under another,so these are called destructive plate boundaries.Earthquake&volcanoes likely to occur.
- Just below the Earth's crust the mantle is fairly solid.
- Further down it is liquid and able to move.
- Convection currents in the mantle cause magma to rise to the surface.
- Force is strong enough to move the solid part of mantle and tectonic plates.
- When the magma reaches the surface,it hardens to form new areas of oceanic crust(seafloor),pushing existing floor outwards.
New oceanic crust is formed continuously at crest of oceanic ridge and old rock is gradually pushed further outwards.
- Earth has magnetic field which reverses every million years or so.
- Combined with seafloor spreading,this produces stripes of rock of alternating polarity.
- Geologist can work out how quickly new crust is forming from width of stripes.
- This occurs at constructive plate boundaries ,where the plates are moving away from each other.
- When an oceanic plate and a continental plate collide,the denser oceanic plate is forced under the continental plate.This is called subduction.
- Oceanic plate then melts ,and the molten rock can rise upwards to form volcanoes.
- Occurs at destructive plate boundaries.
- Mountain ranges form along plate boundaries as sedimentary rock is forced upwards by the pressure created in a collision.
- Earthquakes occur frequently at plate boundaries where plates slide past each other and collide.Pressure builds up over many years due to force of plates pushing against each other.Stored energy is released.
Plate movement plays crucial part in the rock cycle.
- Old rock is desroyed through subduction.
- Igneous rock formed when magma reaches the surface.
- Plate collisions can produce very high temperatures and pressures,causing the rocks to fold and changing sedimentary rock into metamorphic rock.
Evidence for the Structure of the Earth
- Evidence for the layered structure of the Earth has been gained through the study of earthquakes.
- These are due to the fracture of large masses of rock inside the Earth.
- The energy that is released travels through the Earth as a series of shock waves called seismic waves,which are detected using seismographs.
- 2 types of shock waves.P-Waves and S-Waves.Differences in the speed of P-Waves and S-Waves can be used to give evidence for the structure of the Earth.
- Longitudinal waves where the ground is made to vibrate in the same direction as the shock wave is travelling-if the shock wave moves from left to right the ground also vibrates from left to right.
- They can pass through solids&liquids,faster than S-Waves,speed increases in denser material.
Evidence for the Structure of the Earth cont..
- S-Waves-Transverse waves where the ground is made to vibrate at right angles to the direction the shock wave is travelling-if the shock wave is travelling from left to right the ground vibrates up and down.
- Pass through solids only.
- Slower than P-Waves.
- Speed increases in denser material.
Types of Waves
- Waves are regular patterns of disturbance that transfer energy in the direction the wave travels without transferring matter.
- Two types of wave-longitudinal&transverse
- All waves transfer energy from one point to another without transferring particles of matter.
- Each particle moves backwards and forwards in the same plane as the direction of wave movement.
- Each particle simply vibrates to and fro about its normal position.
- Sound travels as longitudinal waves.
- Each particle moves up and down at right angles(90 degrees)to the direction of wave movement.
- Each particle simply vibrates up and down about its normal position.
- Light and water ripples both travel as transverse waves.
Distance Travelled by a Wave
The distance travelled by a wave can be worked out using the formula:
Distance(metres,m)=Wave Speed(metres per second,m/s) x Time(seconds,s)
All waves have several important feautures:
- Amplitude-the maximum disturbance caused by a wave.It is measured by the distance from a crest or trough of the wave to the undisturbed position.
- Wavelength-the distance between corresponding points on two adjacent disturbances.
- Frequency-the number of waves produced per second.Measured in hertz (Hz).
Wave Speed,Wavelength and Frequency
If a wave travels at a constant speed (i.e the speed does not change),then:
- Increasing its frequency will decrease its wavelength.
- Decreasing its frequency will increase its wavelength.
If a wave has a constant frequency(i.e. its frequency does not change),then:
- Decreasing its wave speed will decrease its wavelength.
- Increasing its wave speed will increase its wavelength.
Wave speed equation
Wave Speed(metres per second,m/s)=Frequency(hertz,Hz) x Wavelength(metres,m)
For a constant wave speed,the wavelength is inversely proportional to the frequency.