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

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ocks. Many of these desert deposits are red, because the <strong>we</strong>athering processes there tendto concentrate red hematite on the surfaces of sediment grains. You can investigate howwater currents move and deposit sand using the ‘Mighty river in a small gutter: sedimentson the move’ activity from the http://www.earthlearningidea.com <strong>we</strong>bsite.Each time mud settles outfrom quiet water, in adesert lake, for example,it forms a layer. <strong>The</strong>selayers build up into seriesof laminations. Ifthe mud dries out the surfaceshrinks and it breaksinto mudcracks (desiccationcracks) with polygonalshapes (Figure 1.25).Since mudcracks only developin dried mud, mudcracked mudstones showthat the mud could nothave been deposited in thesea - which would not dryFigure 1.24: Cross bedding insandstones. <strong>The</strong> water flowdirection here was from left torightFigure 1.25: Ancient mudcracks preserved in mudstone.out. <strong>The</strong> mud sometimes carries other clues that it dried out, such as small pits made byraindrops or footprints of the creatures that <strong>live</strong>d there at the time. If salt was depositedon the drying lake floor, the mud can preserve the shapes of the cube-shaped crystals.<strong>The</strong> next mud layer can make casts of these shapes, preserving the shapes of the saltcrystals in mud. All these clues of an environment that was once <strong>we</strong>t but dried out, canbe preserved as the mud becomes mudstone.If desert lakes have sandy floors then waves can form symmetrical ripple marks inthe sand in the same way as they do on beaches and in shallow seas (see Figure 1.26).Unlike current ripple marks, these wave ripple marks are symmetrical, with an equalslope on either side. <strong>The</strong>y are usually straight as <strong>we</strong>ll, and are parallel to the waves thatformed them so, since waves are parallel to shorelines, they can show you the directionof the shoreline of the lake or coast when the ripples formed. Try making your ownripple marks using a washbowl (current ripples) or a tank (wave ripples) as shown on thehttp://www.earthlearningidea.com <strong>we</strong>bsite.Windy deserts are famous for wind-formed sand dunes. <strong>The</strong> winds <strong>we</strong>re not strong enoughto pick up larger particles, so they formed the sand into dunes, and blew any mud-sizedparticles out of the area. <strong>The</strong> sand is therefore <strong>we</strong>ll-sorted and has become rounded andquartz-rich as it was blown along (Figure 1.27). <strong>The</strong> grains often have red hematitestainedsurfaces. Sand is laid down by the wind on the sloping fronts of the dunes in largecross beds, much larger than the cross beds found in rivers. Preserved dune cross beddingcan be a metre or more high. So, desert dune deposits have <strong>we</strong>ll sorted, red-colouredquartz sands deposited in large sets of cross bedded sandstone (see Figure 1.28).15
Figure 1.26: Ancient wave ripple marks preserved in sandstone.Figure 1.27: Modern sand dunes, made of <strong>we</strong>ll-sorted sand deposited in sloping layers onthe front of the dune - Death Valley, California.16
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: Figure 1.20: A close up view of a p
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 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
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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
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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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