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

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Figure 1.34: A melting glacier depositing glacial till.and America, showing that these areas <strong>we</strong>re covered by ice sheets in the past. Other cluesto past glaciation include glacial U-shaped valleys and rocks scratched by the ice draggingrock fragments across their surfaces.<strong>The</strong> fossils that sedimentary rocks contain can be valuable in helping us to interpret theenvironment in which the sediments <strong>we</strong>re laid down. Where possible <strong>we</strong> use the principlethat the ‘present is the key to the past’ (the Principle of Uniformitarianism) to helpus to understand the ancient environment. Coral is a good example of an environmentalindicator, since most coral only grows in shallow tropical seas today so, if <strong>we</strong> find fossilcoral, <strong>we</strong> can assume that the sediments <strong>we</strong>re also deposited in shallow tropical seas (thereis a picture of a fossil coral in Figure 1.35). Similarly, land plants only grow on land or inthe swampy conditions of some coastal areas, so fossil land plants, such as those in Figure1.36, show not only that the area was land, but also, if the growth was very luxuriant andproduced lots of organic material (as in coal), that the area was tropical as <strong>we</strong>ll. Tracks,trails and footprints are important, since they tell us that there <strong>we</strong>re living things in thearea and so it was not too hot, or cold, or dry, or lacking in oxygen or food for organismsto <strong>live</strong> there. Since most tracks, trails and footprints are made on dried-out land or inshallow water, they provide further clues to the environment.When animals have become extinct, <strong>we</strong> cannot use the ‘present is the key to the past’principle so easily. Nevertheless, <strong>we</strong> know that the modern relatives of fossils like trilobites(Figure 1.37) and ammonites (Figure 1.38) only <strong>live</strong> in the sea and so the sediments inwhich they are found are most likely to have been deposited in the sea. Likewise, themodern equivalents of trilobites <strong>live</strong> in shallow waters, indicating that most trilobites also<strong>live</strong>d in shallow sea conditions.Sediments become sedimentary rocks after they become buried, through a process calleddiagenesis that normally takes millions of years (‘millions of years’ is usually abbreviatedto Ma). As the sediments become buried by more and more sediments, they become21
Figure 1.35: A fossil colonial coral preserved in shallow tropical sea sediments.Figure 1.36: Fossilised trees that must have grown on the land.22
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: Figure 1.32: Close up view of a pie
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 and 52: Figure 1.51: Slate, a low-grade met
Page 53 and 54: Figure 1.53: Schist, a medium-grade
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
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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
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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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The planet we live on: The beginnings of the Earth Sciences

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