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Tectonic plates
· Tectonic plates float on the mantle in the upper part of the
earths crust.
· The plates don't stay in one place, they usually move a few
cm per year. This means that places we know e.g. Britain,
have moved slowly over the earths surface.
· When the plates move the mantle underneath rises up
through seafloor, solidifies to form new crust. (it's then
magnetised by the earths magnetic field)
· Every half a million years it swaps direction- the rocks either
have normal polarity or reversed polarity.
· This pattern can be used to estimate the age of different parts
of the crust and see where the plates have moved.…read more

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Sedimentary rocks contain clues to the earths history.
· Because the tectonic plates move, rocks in britain could've
been formed in different places & different climates.
· Geologists look at features of rocks to learn about the
environment in which they were formed: (they look at..)
­ Fossils: remains or imprints of dead organisms, they tell you age of
rock and conditions it was formed in.
­ Shells or ripples on the rock: it tells you it was created by the sea or
rivers.
­ Shapes of grains found in sedimentary rocks: sediment that forms the
rocks will either have been made in air or water. These grains can tell
you if its formed underwater (water borne grains) or on surface
(contains air-blown grains).…read more

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Mineral in the Earths Crust
· Different types of rock in the earths surface contain different minerals.
These minerals are formed by either sedimentation, dissolving,
evaporation, erosion or mountain building.
· Chemical industries grow near where these minerals are found.
Limestone- is a sedimentary rock, it's grey/white and contains mainly of calcium
carbonate. (sedimentary rock is formed by layers of sediment laid down in
lakes/seas.)
· Sediment comes from shells, bones or sea creatures or erosion from existing
rock.
· Erosion creates tiny particles of sediment that wash away and end up at the
bottom of a sea or lake. Over millions of years the layers of sediment get
buried under more, the weight of this squeezes out the water.
· Fluids flowing through pores in the sediment deposit natural mineral cement
that holds the sediment particles together to form rock.…read more

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Coal is another type of sedimentary rock, it's black in colour and
formed over millions of years by fossilisation of layers of plant
matter. Its mainly the element of carbon.
· Some types of coal are hard because they're put under high
pressure and temperatures (this can happen during the mountain
building process).
· Salt is left by evaporation. Salt is extracted by underground
deposits.
· These were formed when ancient seas containing salt evaporated.
The salt left was buried by other layers of sediment over millions of
years.
· This is deposits of rock salt.…read more

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Salt
· Rock salt is a mixture of salt and impurities which is found
underground in salt deposits. It can be extracted by solution mining
or normal mining.
· Normal salt mining- rock salt is drilled, blasted and dug out then
brought to surface by machinery.
· Most salts by normal mining is not pure and used on roads as grit.
Or can be separated out and used to enhance flavour in food or
making chemicals.
· Solution mining is another method where water is injected into a
salt deposit at high pressure. The salt dissolves in the water, making
a solution called brine. It's the pumped back up (it can be used as
brine or can be boiled and left to evaporate, after the impurities are
removed)
· table salt or salt for chemical production is used from this method.…read more

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