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

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into the positions they have today - but they continue moving, at centimetres per year,so the distribution of continents on Earth will continue to change into the future.This movement of plates and continents over geological time has had profound effects;oceans have formed and closed, continents have grown and split, and plate movementshave produced mountain ranges which <strong>we</strong>re later eroded.As the plates and continents <strong>we</strong>re moved across the Earth, they encountered differentclimates in different parts of the globe. So a continent like India, that at one time wasnear the south pole experiencing polar conditions, was moved north, through temperateand tropical zones and across the equator, to its present position. <strong>The</strong> sedimentary rockslaid down when it was in each climate zone record the story of this movement over thesurface of the Earth. <strong>The</strong> rock sequence also records evidence of tension, as plates movedapart, and compression, as plates collided, during its long geological history.As <strong>we</strong>ll as all these changes, that are clearly linked to plate movement, there <strong>we</strong>re globalchanges as <strong>we</strong>ll. At times, global sea levels have been much higher than today. <strong>The</strong>sehigh sea levels seem to be linked to times when new oceans <strong>we</strong>re forming, with activeconstructive plate margins s<strong>we</strong>lling up and displacing much of the ocean water on to theland.Great variations in global climate may also be linked to plate activity so, for example,the intense ice ages that affected Earth bet<strong>we</strong>en 900 and 600 million years ago, may berelated to quieter times in plate movement when reduced volcanic activity at plate marginsproduced less carbon dioxide and the globe cooled. At times during these global coolingevents 600 - 900 million years ago, the Earth may have been completely covered by ice - a‘Snowball Earth’ or nearly covered by ice - a ‘Slushball Earth’. Ice ages which did notaffect the whole globe, but which nevertheless had important effects near the poles alsooccurred around 460 and 300 million years ago and Earth today is still experiencing an iceage that began 2 million years ago. <strong>The</strong>se are called ‘ice house conditions’, contrastingwith the ‘greenhouse conditions’ when the Earth was completely ice-free at the poles.One period of ‘greenhouse conditions’ occurred when Earth experienced extreme globalwarming 55 million years ago.All these events build into a picture of the complex evolution of our <strong>planet</strong> with a numberof major ‘milestones’ along the way (shown in Figure 4.16).Earth is clearly a very dynamic <strong>planet</strong>, with the continents experiencing great changesof latitude and altitude whilst also being affected by global sea level and temperaturechanges. <strong>The</strong>se changes have affected life on Earth by separating and joining populationsof organisms whilst creating and destroying environmental niches. Now humans are havingan additional impact of global importance that can only have more effects on the Earthin the future.107
Millionsof years Some Major Earth Eventsago (Ma)2 Ice age55 Extreme global warming65 Major extinction of life on Earth, including dinosaurs130 First flo<strong>we</strong>ring plants150 First birds190 First mammals200 Major extinction of life on Earth225 First dinosaurs250 Major extinction of life on Earth, including mostmarine organisms300+ Ice ages315 First reptiles325+ Supercontinent Pangaea existed365 Major extinction of life on Earth370 First amphibians420 First plants and animals on land450 Major extinction of life on Earth460 Ice age510 First fish545 First animals with hard parts600 - 900 Ice ages1000+ Supercontinent Rodina existed1200 First multicellular organisms2000 First eukaryotes (cells with a nucleus)3500 First bacteria and archaea (cells with no nucleus)3800 Earliest life4000+ Earliest continents formed4600 Origin of the EarthFigure 4.16: ‘Milestones’ in the evolution of <strong>planet</strong> Earth108
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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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Figure 1.58: A region of folded roc
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Figure 1.61: A normal fault. This s
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Figure 1.64: An unconformity. Older
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proper geological maps. Fossils hav
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Cephalopods are not extinct, but th
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Figure 1.68: A shelled cephalopod f
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You can try the rock sequencing pri
Page 71 and 72: Chapter 2Reading landscapes: how la
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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
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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 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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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
Page 115 and 116: Millionsof yearsago (Ma)01000Some M
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Page 129 and 130: Figure 5.6: An ash eruption rising
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Page 135 and 136: Figure 5.14: A GPS (global satellit
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Page 139 and 140: Figure 5.17: A windfarm in Ireland.
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Page 153 and 154: Figure 6.2: A drilling rig used for
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Page 157 and 158: Figure 6.6: Groundwater flowing out
Page 159 and 160: Dam disaster in Italy, when the wav
Page 161 and 162: Figure 6.10: A slab foundation, bui
Page 163 and 164: An example of this is investigation
Page 165 and 166: GlossaryAbsolute age The</s
Page 167 and 168: Carbon capture The
Page 169 and 170: Crustal shortening This results of
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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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