The planet we live on: The beginnings of the Earth Sciences

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Figure 2.1: Natural lumps and bumps inthe landscape, caused by the effects of underlyingrocks of different toughness and arange of natural surface processes. A viewfrom Glastonbury Tor across the SomersetLevels in South West England.Figure 2.2: Freeze-thaw <strong>we</strong>athering hasforced the cracks in this rock apart.material can be dissolved and removed in solution, but any movement away of solidmaterial is erosion and not <strong>we</strong>athering. Weathering happens in place (in situ) and loosensmaterial that is later removed by erosion.So, physical <strong>we</strong>athering causes the break up of rock surfaces, and the most commontype of physical <strong>we</strong>athering in areas where the <strong>we</strong>ather becomes cold enough to freeze, isfreeze-thaw <strong>we</strong>athering (Figure 2.2). Water is a very unusual substance because whenit becomes solid, its volume increases (usually when liquids become solid, their volumesdecrease). When water freezes, the volume of the ice formed is 9% more than the volumeof the original water. This means when water gets into permeable rocks, bet<strong>we</strong>en thegrains or along cracks, and freezes, it expands and pushes the grains and cracks apart.When it melts, a little more water fills the space and later freezes again. Many cycleslike this eventually <strong>we</strong>aken the rock so that pieces break away, so it has most effect wherethere is frequent freezing and thawing, as on many mountain tops. After being loosened,the broken pieces are moved by erosion, often by gravity, causing them to fall away. Sobeneath rock faces affected by freeze-thaw <strong>we</strong>athering, gravity-erosion has usually builtup a sloping pile of angular rock fragments, called scree (see Figure 2.3). You can seethe effects of freeze-thaw <strong>we</strong>athering on the outsides of walls and buildings as <strong>we</strong>ll, withfragments of brick, stone and concrete building up at the bottom of the wall.Physical <strong>we</strong>athering also affects rocks in desert areas, because they become very hot inthe day and very cold at night (see Figure 2.4). Since different minerals in the rocksexpand and contract at different rates, the rock is <strong>we</strong>akened. This is <strong>we</strong>athering byheating and cooling, and commonly affects granites, where curved sheets can be brokenaway in a process called exfoliation. Lab experiments show that this doesn’t happen tocompletely dry rocks though, so there must be a little water present (often from dew indeserts), causing some chemical <strong>we</strong>athering that <strong>we</strong>akens the rock as <strong>we</strong>ll.57
Figure 2.3: Rock fragments loosened by freeze-thaw <strong>we</strong>athering have been eroded bygravity, falling to make a sloping heap of scree under the rock face.58
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Basic Books in ScienceBook 6<strong
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BASIC BOOKS IN SCIENCE- a Series of
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BASIC BOOKS IN SCIENCE- a Series of
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Looking ahead - If you came across
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3.2 Plate tectonics (20th Century)
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1.30 Coal seams in an opencast coal
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3.4 Alfred Wegener, the polar explo
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5.14 A GPS remote volcano monitorin
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Figure 1.2:minerals.A sandstone roc
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Even diamond can have different col
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Page 55 and 56: Figure 1.56: Metaquartzite, produce
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Page 71: Chapter 2Reading landscapes: how la
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Millionsof years Some Major Earth E
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Figure 5.2: Strike-slip movement (r
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Figure 5.4: The So
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Figure 5.6: An ash eruption rising
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Figure 5.10: A hazard zone map of t
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isk to humans. The
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Figure 5.14: A GPS (global satellit
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None of these methods has yet prove
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Figure 5.17: A windfarm in Ireland.
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Figure 5.19: A beautifully preserve
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Another ‘missing link’ find has
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Figure 5.22: A dinosaur reconstruct
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Figure 5.25: A working aggregate-pr
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Figure 5.26: The E
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Chapter 6Understanding what geologi
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Figure 6.2: A drilling rig used for
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When an oil/gas field has been foun
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Figure 6.6: Groundwater flowing out
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Dam disaster in Italy, when the wav
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Figure 6.10: A slab foundation, bui
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An example of this is investigation
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GlossaryAbsolute age The</s
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Carbon capture The
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Crustal shortening This results of
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Evaporite deposits (or evaporites)
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Geophysical survey Using the method
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“Integrated waste management” <
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Metamorphism The r
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Pore spaces (or pores) Gaps bet<str
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Saltation Sediment movement by flui
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Suspension Sediment movement by flu
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AcknowledgementsPermission to repri
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Figure 2.3 A scree slope. Photo ID:
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Figure 1.15a Hematite.Figure 1.15b
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Figure 1.28 Dune cross bedding in s
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Figure 3.18 An island arc volcano,
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Figure 5.21 Excavations at the dino
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The planet we live on: The beginnings of the Earth Sciences

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