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

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Figure 1.28: Ancient dune cross bedding preserved in a sandstone cliff face.Figure 1.29: Tracks, trails and burrows preserved on a ripple-marked sandstone.In coastal regions, gravel is deposited on shingle beaches, sand is laid down in sandybeaches and on much of the shallow sea floor, and mud is deposited on tidal flats. Beachgravel is usually easily distinguished from other sorts of gravel deposit because the pebbleshave become <strong>we</strong>ll-rounded by the continuous pounding of waves. Beach and shallow seasands can also be distinguished from other sorts of sand because, although they can alsohave bedding, cross bedding and wave ripple marks, they contain much fossil debris too,because coasts and shallow seas have great variety of life and many of the organisms havehard parts that can become fossilised. Similarly, although coastal muds can dry out andhave mudcracks, footprints and rain pits, they also contain abundant life. <strong>The</strong> evidence oflife can be preserved in tidal muds, not only as fossil fragments, but also as whole fossilsand burrows, feeding tracks and trails (as shown in Figure 1.29).When rivers that are loaded with sediment reach the sea, the sediment often builds outinto the sea as a delta. <strong>The</strong> delta is mostly formed of sand but mud is deposited on the17
Figure 1.30: Coal seams in an opencast coal quarry.edges of the delta in the deeper regions. If the delta is in a tropical region, the deltatop becomes covered in vegetation in the swampy tidal conditions. When the swamptrees die through natural life cycles, they fall and build up into thick sequences of organicmaterial. <strong>The</strong>se are the conditions in which coal forms and there are many examples inthe geological record of delta sediments with coal deposits on the top. <strong>The</strong> muds of thefoot of the delta are preserved as shale, above this are the thick sands of the delta itself,often deposited in large cross beds. On top of the delta sands are coal deposits, found ascoal seams (see figure 1.30). Coal mining industries across the world are based on depositslike these.Shallow tropical seas have some of the greatest variety of life on Earth and many of theorganisms that <strong>live</strong> there, from microscopic algae to giant clams, have hard parts madeof calcium carbonate (often calcite, but also a different form of calcium carbonate, calledaragonite). When the organisms die, this material builds up on the sea floor as depositsthat will become limestones. <strong>The</strong>se calcium carbonate deposits are often rich in fossildebris including broken shells, pieces of coral and other carbonate debris. Since mosttypes of coral are only found in tropical seas today, if they are preserved, <strong>we</strong> know thatthe environment must originally have been a tropical shallow sea. <strong>The</strong> photograph (Figure1.31) shows a limestone made of fragments of crinoid, another animal that was commonin some ancient shallow seas. Since calcium carbonate reacts with dilute acid, it is easyto distinguish limestone from other sedimentary rocks, by the one-drop acid test.In shallow tropical sea areas where there is strong evaporation, another type of limestonecan form. It is made of spherical grains of carbonate sand that are rolled around by thewaves and tidal currents. <strong>The</strong> carbonate grains grow as the water evaporates and tinycrystals of aragonite crystallise onto the surfaces of the tiny balls. <strong>The</strong> balls are called18
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: Figure 1.26: Ancient wave ripple ma
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 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
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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
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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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