OCR 21st Century Science - PHYSICS P1

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PHYSICS
P1- The Earth in the Universe
The Earth
When it was first formed, Earth was completely molten (hot liquid). Scientists estimate Earth is 4500
million years old as it has to be older than its oldest rocks. The oldest rocks found on Earth are
about 4000 million years old.
Studying rocks tells us more about the Earth's structure and how it has changed as a result of the
following processes:
Erosion- the Earth's surface is made of rock layers, one on top of the other. The oldest is at the
bottom. The layers are compacted sediment, produced by weathering and erosion. Erosion changes
the surface over time.
Craters- the Moon's surface is covered with impact craters from meteors. Meteors also hit Earth but
craters have been erased by erosion.
Mountain formation- if new mountains weren't formed the Earth's surface would have been eroded
down to sea level.
Folding- some rocks looks as if they have been folding in half. This required huge force over a long
time.
Further evidence of the Earth's age can be found by studying: fossils of plants and animals in
sedimentary rock layers which show how life's changed and the radioactivity of rocks. A rock's
radioactivity decreases over time and radioactive dating measures radiation levels to find out a
rock's age.
The Structure of the Earth
THIN ROCKY CRUST: thickness varies between 10km and 100km, oceanic crust lies beneath the
oceans and continental crust forms continents.
THE MANTLE: Extends almost halfway to the centre, has a higher density and different composition
than rock in the crust and is very hot but under pressure.
THE CORE: Over half of the Earth's radius, made of nickel and iron and has a liquid outer part and solid
inner part and the decay of radioactive elements inside the Earth releases energy, keeping the
interior hot.

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Continental drift
Continental drift theory was produced by Wegener. He saw that the continents had jigsaw fit, with
mountain ranges and rock patterns matching up.
There were also fossils of the same animals on different continents. He said that different continents
had separated and drifted apart. Wegener also claimed that when two continents collided they
forced each other upwards to make mountains.
Geologists didn't except Wegener's theory because...
He wasn't a geologist so was seen as an outsider. The supporting evidence was limited.…read more

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Seafloor spreading
The mantle is fairly solid just below the Earth's crust. Further down it is liquid.
Convection currents in the mantle cause magma to rise. The currents move the solid part of the
mantle and the tectonic plates.
Where the plates are moving apart, magma reaches the surface and hardens, forming new areas
of oceanic crust (seafloor) and pushing the existing floor outwards.
Plate Tectonics
New crust is continuously forming at the crest of an oceanic ridge and old rock is pushed
out.…read more

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The Solar System
The Solar System was formed about 5000 million years ago.
The Solar System started as dust and gas clouds, pulled together by gravity. This created intense
heat. Nuclear fusion began and the Sun (a star) was born. The remaining dust and gas formed smaller
masses which were attracted to the Sun.
Smaller masses in our Solar System are:
Planets: nine large masses that orbit the Sun.
Moons: small masses that orbit planets.
Asteroids: small, rocky masses that orbit the Sun.…read more

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The Universe
The Universe is much older than the Sun, approximately 14000 million years old.
The Speed of Light
Light travels at very high but finite (limited) speeds. If the distance is great enough, light speed can
be measured.
The speed of light is 300 000km/s (around 1 million times faster than sound). Light from Earth
takes just over 1 second to reach the Moon (approximately 384 400km).
Sunlight takes 8 minutes to reach Earth.…read more

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Other Galaxies
If a source of light is moving away from us, the wavelengths of light are longer than if the source is
stationary.
Wavelengths of light from nearby galaxies are longer than scientists expect. This means the galaxies
are moving away from us.
Observations made by Edwin Hubble showed that almost all galaxies are moving away from us
and the further away they are, the faster they are moving away.…read more

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The explanations:
The layer of iridium could be the result of an asteroid collision. A big asteroid would have caused
firestorms, shockwaves and possibly climate change. Dinosaurs couldn't have survived. The collision
could have released sulphur and caused strong acid rain for weeks. Dust could have blocked the Sun
and caused plants to die, affecting the whole food chain.
Scientific explanation
A good scientific explanation will provide some reasons for all of the data. Many explain some facts,
but not all of them.…read more

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