- Mantle is solid beneath crust.
- Liquid futher down.
- Convection currents in mantle cause magma to rise.
- Moves solid mantle and tectonic plates.
- Magma reaches surface and hardens, forms new area of seafloor and pushes old floor outwards.
- Seafloor spreads by few cm every year.
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- Molten when formed.
- 4500 mil years old.
- Learn about Eath structure by studying rocks.
- Earth changed by:
- Erosion: rock layers with oldest at bottom.
- Craters: moon has craters from metoers.
- Mountain formation: if no new mountains formed, Earth's surface erode to sea level.
- Folding: some rocks folded from huge force over time.
- Evidence of Earth's age, study:
- Fossils of plants and animals in sedimentary rock.
- Radioactivity of rocks which decreases over time.
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Structure of Earth
Thin rocky crust:
- 10 - 100km thick.
- Oceanic crust beneath oceans.
- Continental crust forms continents.
- Extends halfway to Earth's centre.
- Higher densisty than crust's rock.
- Hot, under pressure.
- Over half of Earth's radius.
- Nickel and iron.
- Liquid outer, solid inner.
- Radioactive element's decay releases energy and keeps hot.
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- Wegener's theory.
- Continents had jigsaw fit.
- Fossils of same animal on different continents.
- Stated that continents separated and drifted.
- Stated when 2 continents collided, forced upwards to make mountains.
- Geologists didn't accept: Wegener was outsider, limited evidence.
- Seafloor spreading evidence convinced scientific communtiy that Wegener correct.
- Became accepted theory through peer review process.
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- Crust in several large pieces.
- Float on mantle.
- Can move apart, towards or slide past others.
- Plates meet at plate boundaries where volcanoes, earthquakes, mountains occur.
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- Earth magnetic field changes polarity every mil years.
- Combined with seafloor spreading, causes rock stipes of alternating polarity.
- Geologists see how quickly crust forming by width of stripes.
- Subduction - when oceanic and continental plates collide and denser oceanic forced under continental plate.
- Oceanic plate melts, molten rock rises to form volcanoes. At destructive plate boundaries.
- Mountain ranges along colliding plate boundaries as sedimentary rock forced up by pressure of collision.
- Earthquakes occur most at plate boundaries:
- Plates slide past or collide
- Pressure builds up as plates push on each other
- Eventually stored energy released and waves of energy spread from epicentre
- Plate movement crucial in rock cycle:
- Old rock destroyed through subduction.
- Igneous rock formed when magma reaches surface.
- Plate collisions produce high temperatures and pressure - rock folds.
- Sedimentary becomes metamorphic.
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Waves from Earthquakes
- Earthquakes produce wave motions on surface and in Earth.
- Detected using seismograph.
- Primary waves (P-waves):
- Faster than S-waves.
- Travel through liquids and solids.
- Travel through liquid of outer core.
- Secondary waves (S-waves)
- Only through solids.
- Can’t travel through liquid of outer core.
- P-waves and S-waves travel at different speeds in rocks of different density.
- If rock has high density, wave travels faster.
- Boundaries between different types of rock lead to changes in wave speed.
- Causes refraction or reflection of waves.
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Types of Wave
- Particles vibrate backwards and forwards from normal position.
- Particles move backwards and forwards in same plane as direction of wave movement.
- Sound travels as longitudinal waves.
- Particles vibrate up and down from normal position.
- Moves up and down at right angles to direction of wave movement.
- Light and water ripples travel as transverse waves.
- All electromagnteic waves are transverse.
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- Amplitude (distance from trough to top/bottom)
- Wavelength (distance between waves at highest/lowest point)
- Frequency (waves per second in hertz)
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Wave Speed and Frequency
- If wave travels at constant speed:
- Increasing frequency will decrease wavelength.
- Decreasing frequency will increase wavelength.
- Frequency is inversely proportional to wavelength.
- If wave has constant frequency:
- Decreasing wave speed will decrease wavelength.
- Increasing wave speed will increase wavelength.
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Wave speed = Frequency x Wavelength
(m/s) (Hz) (m)
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Distance a Wave Travels
Distance = Wave speed x Time
(m) (m/s) (s)
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The Solar System
- Formed 5000 mil years ago.
- Started as dust and gas clouds, pulled together by gravity.
- This made intense heat - nuclear fusion and Sun born.
- Remaining dust and gas formed smaller masses, attracted to sun.
- Smaller masses:
- Planets - large masses, orbit Sun.
- Moons - small masses, orbit planets.
- Asteroids - small rocky masses, orbit Sun.
- Comets - small icy masses, orbit Sun.
- Dwarf planets - small masses, orbit Sun.
- Planets, moons and asteroids move in elliptical orbits.
- Comets move in highly elliptical orbits.
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- 500 million years older than Earth.
- Energy from nuclear fusion:
- Hydrogen atoms fuse together to produce atom with larger mass.
- Binding energy stored in hydrogen atoms is released.
- All chemical elements larger than helium formed by nuclear fusion in earlier stars.
- Nuclei of hydrogen atoms fuse together during nuclear fusion.
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- Approximately 14,000 million years old.
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Speed of Light
- Light travels at high but finite (limited) speeds.
- If distance great enough, speed of light can be measured.
- Speed of light through space 300000km/s, takes just over 1 second to reach moon.
- Sunlight takes 8 mins to reach Earth.
- Space distances measured in light-years.
- Nearest galaxy to Milky Way is 2.2 mil light-years away.
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Measuring Distances in Space
- Relative brightness– thedimmer a star, thefurther away but never certain.
- Parallax– stars in near distance appear to move against background of distant stars, the closer they are, more they appear to move. Further away the star, less accurate measurement.
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- Radiation from stars tells us what we know about them.
- Stars produce visible light, ultraviolet and infrared.
- Light pollution when electric lights on Earth make viewing stars difficult.
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- If source of light is moving away, wavelengths longer than if source is stationary.
- Wavelengths of light from nearby galaxies longer than scientists expect so galaxies moving away.
- Observations by Hubble showed:
- Almost all galaxies moving away.
- The further away they are, the faster they’re moving.
- Hubble’s Law: The speed that galaxy's moving away proportional to its distance from us.
- This means the Universe is expanding.
- If an electromagnetic wave appears longer than it should, been red shifted so moving away.
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Relative Sizes to Universe
- Diameter of Earth = 12742km.
- Diameter of Sun = 110 x Earth’s diameter.
- Size of Earth’s orbit = 107 x diameter of Sun.
- Distance of Sun to nearest star = 4 light-years.
- Size of solar system = several thousand light-years.
- Size of Milky Way = 100000 light-years.
- Distance of Milky Way to nearest galaxy = 2.2 million light-years.
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The Beginning and The End
- Big Bang theory says Universe began with huge explosion 14000 million years ago.
- If there isn’t enough mass, the Universe will keep expanding.
- If there’s too much mass the Universe will collapse.
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