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

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Figure 3.30: A graph of observed increases in seal level over the past 50 years withprojections of the effects of the melting of continental ice sheets in the next 100 years.Many low lying areas of Earth would be very vulnerable to an increase in sea level of halfa metre, including most of Earth’s major cities, which have been built in coastal areas. Ifsea level continued to rise, the impacts would be even greater.<strong>The</strong> geological record contains evidence of sea level change in the recent geological past.During the glacial periods shown in Figure 3.26, such as the one 20,000 years ago, moreof the Earth’s water was locked up as ice on land than now, so sea level was lo<strong>we</strong>r andareas now under water <strong>we</strong>re once land. Thus at low tide in some coastal areas <strong>we</strong> canfind tree stumps of ancient submerged woodland, and these are sometimes found with theartifacts of the humans that <strong>live</strong>d in the area at the time. Meanwhile, river valley systemscut when sea level was lo<strong>we</strong>r, <strong>we</strong>re flooded as sea level rose forming ‘drowned valleys’, orestuaries on which many of today’s ports are based. It is thought that some importanthuman migrations took place during times of lo<strong>we</strong>r sea level, such as the native Americanmigration from eastern Asia into North America through the area that is now Alaska andthe migration of people into the British Isles, before they became islands.During periods bet<strong>we</strong>en the glaciations, also shown on Figure 3.26 (eg. 120,000 yearsago), less ice was locked up in continental ice sheets and so sea levels <strong>we</strong>re higher. Incoastal areas, beaches <strong>we</strong>re formed at higher levels than today and have now been left as‘raised beaches’ several metres above today’s sea level, often with ‘fossil cliffs’ behindthem.One of the founders of the science of climate change was Charles Keeling who, in 1958,first started to measure the amount of carbon dioxide in the atmosphere accurately. He93
Figure 3.31: <strong>The</strong> ‘Keeling Curve’ of atmospheric carbon dioxide measurements, showingannual cycles and a steady increase.built a high-precision measuring instrument and sited it on top of a volcanic peak inHawaii, to be as far away from and as high above human polluting activities as possible.He was asked to make just one measurement, but thought it would be more effective tomake regular measurements. To the great surprise of scientists, he found that the carbondioxide content of the atmosphere varied annually. He also found that, in addition to thisannual variation, it also sho<strong>we</strong>d a steady increase, as can be seen in Figure 3.31.<strong>The</strong> annual variations in the ‘Keeling Curve’, as it has now been called, are explainedbecause of seasonal variation of uptake of carbon dioxide by plants. <strong>The</strong>re is more land,and so more plants in the Northern Hemisphere than in the Southern Hemisphere. Sowhen, in the Northern Hemisphere summer, plants are most active, they remove carbondioxide from the atmosphere; thus the curve reaches its lo<strong>we</strong>st point at the end of theNorthern Hemisphere summer, in October. It then recovers, to reach its highest pointat the beginning of the Northern Hemisphere summer, in May. This annual cycle issometimes described as the ‘breathing’ of the Earth.As described above, most scientists believe that the steady increase of carbon dioxide,shown by the curve over the past 50 years, is the result of the burning of carbon-richfossil fuels by humans, ie. it is an anthropogenic effect (anthropo - human; genic - causedby). Ho<strong>we</strong>ver, some scientists think that global warming of the oceans releases carbondioxide causing this increase - so the debate continues. Ho<strong>we</strong>ver, without the crucial workof Keeling, who first demonstrated that the carbon dioxide content of the atmosphere isincreasing, such a debate couldn’t have taken place.94
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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
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Figure 1.49: An old slate quarry, s
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Figure 1.51: Slate, a low-grade met
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Figure 1.53: Schist, a medium-grade
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Figure 1.56: Metaquartzite, produce
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Page 61 and 62: Figure 1.64: An unconformity. Older
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Page 65 and 66: Cephalopods are not extinct, but th
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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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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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