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

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Figure 6.5: Electrical resistivity surveying.and arsenic and silver for gold deposits. Heavy mineral surveys could find titaniumores, diamonds and gold. Geochemical and heavy mineral surveys begin by sampling thestream sediments of a region and sending the samples to labs for analysis. Any anomaliesare follo<strong>we</strong>d up, upstream, by more intense stream sampling and later by soil sampling,normally on a grid pattern, to pinpoint the source of the anomaly.Mineral exploration geologists spend most of their time in the field, often in large anddeveloping countries where the geological potential is least <strong>we</strong>ll known. Mining geologistsare based in mines, which may often be in remote areas. <strong>The</strong>y explore rock sequences andore deposits ahead of the miners, using evidence from surface or underground drilling butsometimes with geophysical methods as <strong>we</strong>ll. This is important rock detective work, sincethe work of the miners and the profit of the mining company is based on the decisions ofthe mining geologist.Geological work with the mining industry fluctuates with world and local economies, butthere will always be need for natural resources and the expertise of mineral explorationand mining geologists (Figure 6.1).6.4 HydrogeologyHydrologists study the whole of the water cycle, both above and below ground, buthydrogeologists focus particularly on subsurface water, called groundwater. Whenit rains, water infiltrates into the ground and percolates down into the rocks beneath.141
Figure 6.6: Groundwater flowing out of thebedrock in a spring.Figure 6.7: Water flows down through theunsaturated zone to the water table andthen flows sideways as groundwater, emergingnaturally in springs or rivers.If these rocks are permeable the water will continue to run down until it reaches thesaturated zone, where all the pore spaces are full of water. <strong>The</strong> top of this zone iscalled the water table and you can often see the top of the water table by looking downa <strong>we</strong>ll. <strong>The</strong> water table is not flat but is higher under hills and lo<strong>we</strong>r beneath valleys,so the groundwater flows slowly downhill, towards the valleys. Where the water tablereaches the ground surface, water flows out of the ground, in a spring, marsh or bog, ordirectly into rivers, lakes or the sea.A permeable rock containing water is called an aquifer. If part of the aquifer is beneathan impermeable layer, this is a confined aquifer (Figure 6.7). Boreholes drilled intoaquifers to extract water are called <strong>we</strong>lls and if <strong>we</strong>lls are drilled into confined aquifers,water may flow naturally out of the <strong>we</strong>ll under pressure.<strong>The</strong> job of the hydrogeologist is to find aquifers in places where there is not enough surfacewater from rivers or reservoirs to supply the population. When the hydrogeologist hasexamined the regional geology and found areas where there are likely to be permeablerocks containing groundwater, an exploratory <strong>we</strong>ll is drilled. If the <strong>we</strong>ll hits water, thewater may naturally flow out of the ground, if the aquifer was confined, but normally, thewater will need to be pumped from the <strong>we</strong>ll.When a possible aquifer is found, the hydrogeologist will investigate if the <strong>we</strong>ll can producea reliable water supply by carrying out pumping tests. A series of test <strong>we</strong>lls is drilledin a line on either side of the first borehole. <strong>The</strong>n water is pumped from the centralborehole. This causes the water table to be drawn down to form a ‘cone of depression’around the pumping borehole and the shape of the cone of depression can be found bymeasuring the height of the water in the test <strong>we</strong>lls. If the sides of the cone of depressionare steep, the rock is not very permeable, water flows only slowly into the pumping <strong>we</strong>lland will not produce enough reliable water. Ho<strong>we</strong>ver, if the cone of depression is broad,water flows easily into the pumping <strong>we</strong>ll from the surrounding rock and a reliable watersource has been found.142
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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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Figure 1.8: A red garnet crystal in
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Figure 1.12: Crystals of minerals i
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Hematite, Fe 2 O 3 - earthy red, me
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Figure 1.17: Sedimentary rocks show
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Figure 1.20: A close up view of a p
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Figure 1.26: Ancient wave ripple ma
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Figure 1.30: Coal seams in an openc
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Figure 1.32: Close up view of a pie
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Figure 1.35: A fossil colonial cora
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Figure 1.38: Fossil ammonites, indi
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Figure 1.39: ‘Massive’ igneous
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Figure 1.41: A close up view of a p
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Figure 1.44: A basalt flow that coo
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Figure 1.47: Deposit of volcanic as
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Figure 1.49: An old slate quarry, s
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Figure 1.51: Slate, a low-grade met
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Figure 1.53: Schist, a medium-grade
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Figure 1.56: Metaquartzite, produce
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Figure 1.58: A region of folded roc
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Figure 1.61: A normal fault. This s
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Figure 1.64: An unconformity. Older
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proper geological maps. Fossils hav
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Cephalopods are not extinct, but th
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Figure 1.68: A shelled cephalopod f
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You can try the rock sequencing pri
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Chapter 2Reading landscapes: how la
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Figure 2.3: Rock fragments loosened
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Figure 2.6: The jo
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Figure 2.10: The m
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are forming them. Similarly the sha
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Figure 2.19: This photo was taken f
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Figure 2.25: Dinosaur tracks conser
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• On coastal sections, whenever p
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found evidence that the Earth was a
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Figure 3.3: James Hutton, the ‘Fo
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Figure 3.5: A page of Wegener’s 1
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Figure 3.7: The st
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Figure 3.10: The r
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Figure 3.13: The m
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Figure 3.15: The S
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Figure 3.19: An ocean versus contin
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Figure 3.23: Map of the major tecto
Page 105 and 106: Figure 3.26: Global temperature cha
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Page 109 and 110: Figure 3.31: The
Page 111 and 112: planet extended th
Page 113 and 114: Figure 4.1: William Smith’s geolo
Page 115 and 116: Millionsof yearsago (Ma)01000Some M
Page 117 and 118: ocks whilst the first definite plan
Page 119 and 120: Figure 4.9: The ch
Page 121 and 122: Figure 4.12: The 4
Page 123 and 124: Millionsof years Some Major Earth E
Page 125 and 126: Figure 5.2: Strike-slip movement (r
Page 127 and 128: Figure 5.4: The So
Page 129 and 130: Figure 5.6: An ash eruption rising
Page 131 and 132: Figure 5.10: A hazard zone map of t
Page 133 and 134: isk to humans. The
Page 135 and 136: Figure 5.14: A GPS (global satellit
Page 137 and 138: None of these methods has yet prove
Page 139 and 140: Figure 5.17: A windfarm in Ireland.
Page 141 and 142: Figure 5.19: A beautifully preserve
Page 143 and 144: Another ‘missing link’ find has
Page 145 and 146: Figure 5.22: A dinosaur reconstruct
Page 147 and 148: Figure 5.25: A working aggregate-pr
Page 149 and 150: Figure 5.26: The E
Page 151 and 152: Chapter 6Understanding what geologi
Page 153 and 154: Figure 6.2: A drilling rig used for
Page 155: When an oil/gas field has been foun
Page 159 and 160: Dam disaster in Italy, when the wav
Page 161 and 162: Figure 6.10: A slab foundation, bui
Page 163 and 164: An example of this is investigation
Page 165 and 166: GlossaryAbsolute age The</s
Page 167 and 168: Carbon capture The
Page 169 and 170: Crustal shortening This results of
Page 171 and 172: Evaporite deposits (or evaporites)
Page 173 and 174: Geophysical survey Using the method
Page 175 and 176: “Integrated waste management” <
Page 177 and 178: Metamorphism The r
Page 179 and 180: Pore spaces (or pores) Gaps bet<str
Page 181 and 182: Saltation Sediment movement by flui
Page 183 and 184: Suspension Sediment movement by flu
Page 185 and 186: AcknowledgementsPermission to repri
Page 187 and 188: Figure 2.3 A scree slope. Photo ID:
Page 189 and 190: Figure 1.15a Hematite.Figure 1.15b
Page 191 and 192: Figure 1.28 Dune cross bedding in s
Page 193 and 194: Figure 3.18 An island arc volcano,
Page 195 and 196: Figure 5.21 Excavations at the dino
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