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

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Figure 1.52: Bedding and cleavage seen in slate, formed from mudstone by regional metamorphism.<strong>The</strong> bedding runs steeply from the lo<strong>we</strong>r right to the upper left and is shownby the different bands of colour. <strong>The</strong> cleavage is the series of cracks that slope up gentlyfrom right to left. <strong>The</strong> tectonic forces that caused the metamorphism <strong>we</strong>re at right anglesto the cleavage, from top to bottom of the photo.1.6 Deformation in rocks - geological structuresRocks in the Earth’s crust can be put under pressure by three different sets of forces:they can be compressed by compressional stresses; they can be pulled apart by tensionalstresses; or they can, under pressure, slide past one another due to shear stresses. <strong>The</strong>reis a fourth type of stress, caused by turning forces, but these are not geologically verycommon.Not only do three types of stress commonly affect crustal rocks, but rocks respond inthree different ways. <strong>The</strong> rock can absorb the stress, like a rubber ball, but when thestress is removed, it bounces back. This is called elastic behaviour and, although as <strong>we</strong>shall see, this is important in earthquakes, the effects cannot be seen in rocks, since theyhave sprung back elastically to their original shape and size. <strong>The</strong> rocks may bend andflow, like clay does when you mould it with your hands. This is ductile behaviour, therocks remain distorted into folds that can be seen clearly. Finally the rocks may break;this is brittle behaviour and results in different forms of rock fracture.Whether a rock bends, breaks or behaves elastically under stress depends on a rangeof different factors, including what the rocks are made of, how great the stress is, thetemperature of the rocks, how deeply buried they are, and for how long the stresses areapplied. <strong>The</strong> result is that the same rock can behave differently at different times andunder different conditions and can show the effects of both ductile and brittle behaviour;so folded rocks can be fractured as <strong>we</strong>ll.37
Figure 1.53: Schist, a medium-grade metamorphic rock, formed by the continued metamorphismof slate, by higher temperatures and pressures. <strong>The</strong> foliation gives this flatsurface of aligned platy minerals.38
Page 1 and 2: Basic Books in ScienceBook 6<strong
Page 3 and 4: BASIC BOOKS IN SCIENCE- a Series of
Page 5 and 6: BASIC BOOKS IN SCIENCE- a Series of
Page 7 and 8: Looking ahead - If you came across
Page 9 and 10: 3.2 Plate tectonics (20th Century)
Page 11 and 12: 1.30 Coal seams in an opencast coal
Page 13 and 14: 3.4 Alfred Wegener, the polar explo
Page 15 and 16: 5.14 A GPS remote volcano monitorin
Page 17 and 18: Figure 1.2:minerals.A sandstone roc
Page 19 and 20: Even diamond can have different col
Page 21 and 22: Figure 1.8: A red garnet crystal in
Page 23 and 24: Figure 1.12: Crystals of minerals i
Page 25 and 26: Hematite, Fe 2 O 3 - earthy red, me
Page 27 and 28: Figure 1.17: Sedimentary rocks show
Page 29 and 30: Figure 1.20: A close up view of a p
Page 31 and 32: Figure 1.26: Ancient wave ripple ma
Page 33 and 34: Figure 1.30: Coal seams in an openc
Page 35 and 36: Figure 1.32: Close up view of a pie
Page 37 and 38: Figure 1.35: A fossil colonial cora
Page 39 and 40: Figure 1.38: Fossil ammonites, indi
Page 41 and 42: Figure 1.39: ‘Massive’ igneous
Page 43 and 44: Figure 1.41: A close up view of a p
Page 45 and 46: Figure 1.44: A basalt flow that coo
Page 47 and 48: Figure 1.47: Deposit of volcanic as
Page 49 and 50: Figure 1.49: An old slate quarry, s
Page 51: Figure 1.51: Slate, a low-grade met
Page 55 and 56: Figure 1.56: Metaquartzite, produce
Page 57 and 58: Figure 1.58: A region of folded roc
Page 59 and 60: Figure 1.61: A normal fault. This s
Page 61 and 62: Figure 1.64: An unconformity. Older
Page 63 and 64: proper geological maps. Fossils hav
Page 65 and 66: Cephalopods are not extinct, but th
Page 67 and 68: Figure 1.68: A shelled cephalopod f
Page 69 and 70: You can try the rock sequencing pri
Page 71 and 72: Chapter 2Reading landscapes: how la
Page 73 and 74: Figure 2.3: Rock fragments loosened
Page 75 and 76: Figure 2.6: The jo
Page 77 and 78: Figure 2.10: The m
Page 79 and 80: are forming them. Similarly the sha
Page 81 and 82: Figure 2.19: This photo was taken f
Page 83 and 84: Figure 2.25: Dinosaur tracks conser
Page 85 and 86: • On coastal sections, whenever p
Page 87 and 88: found evidence that the Earth was a
Page 89 and 90: Figure 3.3: James Hutton, the ‘Fo
Page 91 and 92: Figure 3.5: A page of Wegener’s 1
Page 93 and 94: Figure 3.7: The st
Page 95 and 96: Figure 3.10: The r
Page 97 and 98: Figure 3.13: The m
Page 99 and 100: Figure 3.15: The S
Page 101 and 102: Figure 3.19: An ocean versus contin
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Figure 3.23: Map of the major tecto
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Figure 3.26: Global temperature cha
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Figure 3.29: A computer generated p
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Figure 3.31: The
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planet extended th
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Figure 4.1: William Smith’s geolo
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Millionsof yearsago (Ma)01000Some M
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ocks whilst the first definite plan
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Figure 4.9: The ch
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Figure 4.12: The 4
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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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