AQA GCSE Geography A rocks, resources and scenery revision notes

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How were rocks formed?
What is the geological timescale?
Geological timescale is the period of geological time since life became abundant 542 million years
ago, which geologists have divided into eras and periods. There are three main eras: Cenozoic,
Mesozoic and Paleozoic.
The three main rocks are:
Granite (formed 280 million years ago)
Carboniferous limestone (formed 340 million years ago)
Chalk (formed during the cretaceous period)
Clare (formed don many occasions throughout time period)
Rock types
Rock type Formation Characteristics Examples Photo
Igneous Formed by cooling of Composed of EXTRUSIVE
molten magma interlocking LAVAS:
underground crystals Basalt, andesite
(intrusive) or on the (crystalline). They and rhyolite.
ground (extrusive by are tough and INTROCIVE:
volcanic activity). resistant to Granite, gabbro
erosion. and dolerite.
Sedimentary Formed by the Usually form Sandstone,
compaction and layers called limestone, shale,
cementation of beds. Often they clay and
sediments; usually contain fossils. mudstone. The
deposited in the sea. Some rocks can rock chalk is a
Also includes organic be tough (e.g. form of
materials e.g. coal) limestone) most limestone.
and rocks are weaker than
precipitated from igneous or
solutions (e.g. metamorphic.
Metamorphi Formed buy the Often crystalline. Slate is the most
c alteration of They exhibit common. Others
pre-existing igneous layering called are gneiss and
or sedimentary or cleavage and schist.
metamorphic rocks banding. They
by heat and/or tend to be tough
pressure. and resistant to

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The rock cycle
What is weathering and how does it operate?
What is weathering?
Weathering is the disintegration or decay of rocks in their original place oat or close to the ground
Types of weathering
1. Mechanical weathering ­ also known as physical weathering, this involves the disintegration
(breakup) of rocks without any chemical changes tracking place. It often results in piles of angular
rock fragments called scree found at the foot of bare rocky outcrops.
2.…read more

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Biological weathering ­ this involves the action of flora and fauna. Plant roots are effective a t
growing and expanding in cracks in the rocks. Rabbits can burrow into weak rocks e.g. sand.
Mechanical weathering
Freeze thaw weathering
Commonly associated with large fluctuations in temperature,
which occur partially in hot deserts. Rock is a poor conductor
of heat. This means that only the outer part of a rock warms
and cools in response to changes in temperature.…read more

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The weathering of limestone and chalk by rainwater. It affects rocks made of calcium carbonate.
What are the characteristics of granite
The formation and distribution of granite
Granite is an intrusive igneous rock that was formed deep underground. Following uplift and the
erosion of the overlaying rocks the granite has been exposed on the surface.
In south-west England there are isolate exposures of granite all part of the same rock mass called a
batholith.…read more

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Granit contains joints. Joints form when the granite cooled and contracted. Horizontal joints in granite
resulted from pressure release as the overlying rocks were moved by erosion. The rock expanded as
the pressure was released, causing these cracks to form parallel to the ground surface. The presence
of these joints makes granite vulnerable to freeze-thaw weathering and, in some places, exfoliation.
Despite the presence of joints granite is an impermeable rock and granite landscapes are often wet
and marshy with plenty of rivers.…read more

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What are the characteristics of chalk and clay
Chalk and clay are two examples of sedimentary rocks. They were both formed under the sea and
then uplifted by tectonic activity to form rocks.
Characteristics of chalk and clay
Chalk is a permeable rock meaning there are few rivers around it (causing a lack of erosion). It is
permeable because it is heavily jointed and porous. Rainwater soaks through the joints until it reaches
the water table. This is the upper surface of underground water.…read more

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The characteristics of carboniferous limestone
Carboniferous limestone is a tough and resistant rock. It forms upland areas e.g. Pennine Hills and
Mendips. When exposed to coast, as in some parts of south Wales, if forms dramatically towering
Despite being physically strong it is chemically weak. As it is composed of calcium carbonate it is
vulnerable to carbonation. It is well jointed, with horizontal joints called bedding planes and between
the beds there are regularly spaced vertical joints. These increase freeze-thaw weathering.…read more

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An example is Malham.
Swallow holes:
An enlarged joint into which water falls.
These happen when a stream dissolves a joint in
the limestone and then flows down in.
An example is Gaping Gill.
Dry valleys:
A valley formed by a river in a wetter period but
now with no river.
These are old river valleys. They show what a river
once flowed over the surface ­ possibly during the
last Ice Age, when the ground was frozen or
afterwards when the ground was saturated.…read more

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Underground caverns:
A large underground cave.
These develop when water flows underground
through joints or swallow holes and then weathers
and erodes the limestone beneath. Eventually
large cave systems can form.
An example is Gaping Gill.
An icicle-like calcite feature hanging down from a
cavern roof.
These are formed by the dripping of water from
the roof. Some of the water evaporates and
calcium carbonate is deposited to form the
A stumpy calcite feature formed on a cavern floor.…read more

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Kitchen surfaces. pastures and reservoirs have Granite forms in
harsh been created in wild moorland.
Kaolin (china clay) environmental steep valleys e.g.
originated from conditions. Burrator Attractive for
granite. Reservoir which outdoor activities
This is because supplies e.g. walking, bird
granite forms in Plymouths water. watching, biking
upland areas and climbing.
Water sports in
Chalk Quarried to be Reasonable Important source Characterized by
manufactured fertile land, used of underground rolling hills.
into cement. for sheep farming water (aquifers).…read more



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