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

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Figure 3.16: <strong>The</strong> age of the ocean floor, from the youngest in red to the oldest in blue.Figure 3.17: An ocean versus ocean destructivemargin, with an oceanic trenchand an arc of destructive andesitic volcanoes.Figure 3.18: This volcano in Java showsthe typical conical shape of central-vent andesiticvolcanoes that form island arcs.85
Figure 3.19: An ocean versus continent destructivemargin, with an oceanic trenchand a mountain range with volcanoes.Figure 3.20: This volcano in Alaska hasthe conical shape of most continental volcanoes.When an oceanic plate meets a plate carrying a continent, the continental rocks are muchless dense than the oceanic rocks, so it is the oceanic plate that is subducted (Figure 3.19).<strong>The</strong> subducting plate forms an oceanic trench and causes earthquakes. <strong>The</strong> plate partiallymelts here too, forming intermediate magma that rises to form andesitic volcanoes withconical shapes (Figure 3.20).Ho<strong>we</strong>ver, this rising magma also melts the rock at the base of the continental crust. Whenthe continental crust partially melts, it is the low melting point, silicon-rich minerals thatmelt first, leaving those richer in iron behind. This melt is a silicic melt, even richerin silicon than intermediate magma. If these magmas reach the surface, they are evenmore viscous than andesitic melts, and produce steep-sided volcanoes with catastrophiceruptions. But most of the magma is so viscous and slow-moving that it never reaches thesurface; it cools down slowly below ground in bubble-shaped plutons several kilometersacross. <strong>The</strong>se granite plutons form deep in the roots of mountain chains. <strong>The</strong> mountainchains are produced by compression as the two plates are forced together, causing folding,thrust faulting and regional metamorphism as <strong>we</strong>ll as igneous activity.When two plates meet and both are carrying continents, neither can subduct, since thedensity of both of them is too low. So the two continental plates are forced togetherproducing enormous compressional forces and creating great mountain chains as the rocksbet<strong>we</strong>en them are deformed, metamorphosed and intruded by granites (Figure 3.21). <strong>The</strong>rocks are deformed into tight folds and slabs of crust can be moved many kilometres alongthrust faults. <strong>The</strong> collision of India with Asia in the fairly recent geological past hasformed the highest altitude mountain range on Earth, the Himalayas. Since after a timethe plates become locked, no further subduction occurs so these great mountain ranges donot have volcanic activity nowadays. But since the plates are still being moved towardsone another, major catastrophic earthquakes can occur. In these areas of steep slopes andgreat erosion, the earthquakes often trigger landslides too, increasing the danger of theseactive geological regions.86
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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
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
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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
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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
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Page 107 and 108: Figure 3.29: A computer generated p
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Page 113 and 114: Figure 4.1: William Smith’s geolo
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Page 129 and 130: Figure 5.6: An ash eruption rising
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Page 139 and 140: Figure 5.17: A windfarm in Ireland.
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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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