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

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Figure 1.54: Gneiss, a high-grade metamorphic rock, formed by the continued metamorphismof schist by even higher temperatures and pressures, or by the high-grade metamorphismof granite. <strong>The</strong> high pressures deformed the bands of gneiss into tight foldsbefore this rock was intruded by a narrow dyke.Figure 1.55: Marble, produced by the metamorphism of limestone either by high temperaturesin thermal metamorphism, or by high temperatures and pressures in regionalmetamorphism. This specimen clearly shows the interlocking crystal texture.39
Figure 1.56: Metaquartzite, produced by the metamorphism of pure quartz sandstone,by either thermal metamorphism or regional metamorphism. This photo shows the interlockingquartz grain texture that makes it such a tough rock.So <strong>we</strong> have three types of stress and three types of behaviour, and you might anticipateseeing the results in rocks in nine different ways. Ho<strong>we</strong>ver, as <strong>we</strong> don’t see the effectsof elastic behaviour, this cuts this number down to six. When rocks are pulled apart bytensional stresses and flow, the main effect is that the layers become thinner and it isusually impossible to tell that this has happened. We rarely see the ductile effect of shearstresses in rocks either, so <strong>we</strong> are left with only four common effects to examine below.When rock sequences are strongly compressed and flow, <strong>we</strong> see the effects as folding ofthe layers. <strong>The</strong> rocks may be deformed into gentle open folds or into a series of tightfolds. <strong>The</strong> place where the rock has bent most is called the fold axis. Since there isnever just one layer that is bent, but many, if you join the axes of all the folded layerstogether, a plane is formed and this is called the axial plane surface. Compressionalstresses always act at right angles to the fold axial plane surfaces, so <strong>we</strong> can use the shapeof the folds to work out the directions of the stresses that deformed them. <strong>The</strong> directionsof axial planes are measured as compass directions; folds with north/south axial planesmust have been formed by east/<strong>we</strong>st stresses.Where rocks are folded, you often can’t see the folds themselves, you just see the sides orlimbs of the fold, as layers that <strong>we</strong>re once horizontal but are now sloping. <strong>The</strong> directionof downward slope is called the dip and can be measured as an angle to the horizontal. Atright angles to the dip direction is the strike, which is measured with a compass. So rocksthat dip towards the east have a north/south strike, which is parallel to the directionsof the fold axial plane surface. This may sound complicated but you can make a simplemodel to explain it by using your hands. Put the sides of your hands, with the littlefingers together, into a downfold, with both hands sloping at the same angle. <strong>The</strong> fold40
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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 and 52: Figure 1.51: Slate, a low-grade met
Page 53: Figure 1.53: Schist, a medium-grade
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
Page 103 and 104: 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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