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

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Figure 5.20: One of the strange animals found exceptionally preserved in the 505 millionyear old Cambrian Burgess Shale in Canada.debated whether these strange animals are related to modern animal groups or not andwhat this means for the evolutionary story - and the debate continues. This debate wouldnot have been possible if the unusual fossilisation circumstances had not preserved thespecimens so completely.Examples of rock sequences with exceptional preservation like this are called lagerstättenand only about 50 examples of lagerstätten are known from the whole geological record.Ho<strong>we</strong>ver, these have given scientists unique ‘windows’ into the variety and detail of lifeat key times in the Earth’s past.Another example of lagerstätten is the Jurassic Solenhofen Limestone in Germany (about150 million years old) in which fossils of Archaeopteryx have been found (see Figure 5.19).As in other lagerstätten, the Archaeopteryx fossils are beautifully preserved and it is clearthat they not only had small teeth, like reptiles, but feathers like birds as <strong>we</strong>ll.Before the finding of Archaeopteryx scientists had debated long and hard how birds hadevolved. <strong>The</strong> Archaeopteryx specimens, with many features similar to dinosaurs (types ofreptiles), but also with wings and feathers, sho<strong>we</strong>d how birds evolved from reptiles andso provide a ‘missing link’ in evolutionary history.127
Another ‘missing link’ find has recently been reported. <strong>The</strong> headline in a UK newspaperread ‘Fossil Ida: Extraordinary find is ‘missing link’ in human evolution’ (theGuardian newspaper, 19 May 2009). <strong>The</strong> article continued, ‘Scientists have discovered anexquisitely preserved ancient primate fossil that they believe forms a crucial “missing link”bet<strong>we</strong>en our own evolutionary branch of life and the rest of the animal kingdom.’ <strong>The</strong>newspaper story described the fossil which, very unusually, was 95% complete, with thehair, and even the last meal of the small animal preserved. It was a young female about 6to 9 months old that may just have left its mother, and was found in sediments depositedin a volcanic lake 47 million years ago. It forms a ‘missing link’ bet<strong>we</strong>en early smallprimate animals and the group that later evolved into monkeys, apes and eventually,humans.Some media reports and many cinema films/movies suggest that the skeletons of largeanimals are often found intact in sedimentary rock layers. This only happens in reallyexceptional circumstances, as with ‘Ida’ above. Much more common is the finding of separatebones, like the one being excavated in Figure 5.21. <strong>The</strong> bones are usually separatedbecause, after the animal died many things could happen before the bones <strong>we</strong>re buried.Scavenging animals may have pulled the bones apart and che<strong>we</strong>d up the smaller bones,the animal may have rotted so that the skeleton fell apart, or it may have been s<strong>we</strong>ptaway and broken up in a river or the sea. When groups of bones are found together,geoscientists usually try to reconstruct the animal to show what it was like when it wasliving. When this was first done, many mistakes <strong>we</strong>re made. In the famous case of Iguanadon,early reconstructions sho<strong>we</strong>d a ‘spike’ on the nose, but it was later found to beone of the two thumb spikes.When skeletons are reconstructed today, evidence is used from several skeletons, from thesize and shape of the bones including the scars left by muscles, from how similar modernanimals <strong>live</strong>, and from features like footprints that show how the animal moved. So,modern skeleton reconstructions are much more accurate, and realistic working modelsand animations can be made, like those in the ‘Walking with dinosaurs’ TV programmesand exhibition. Most of the details of these models and animations are as accurate as theycan be, although <strong>we</strong> are never likely to know the exact colours of the skins, the soundsthe animals made, or the detailed ways in which they <strong>live</strong>d (as in Figure 5.22).<strong>The</strong> search for early human fossils is even more difficult, since they <strong>we</strong>re much less commonthan many dinosaur groups and they usually <strong>live</strong>d on land <strong>we</strong>ll away from environmentswhere they might be fossilised. So scientists and media reports are often very excited byvery small human-related finds.When a skeleton was found in rocks more than 3 million years old in Ethiopia, with partsof nearly all the major bones preserved, there was huge excitement. This was a fossil ofan early type of hominid called Australopithecus on the evolutionary line that eventuallyproduced Homo sapiens, humankind. This fossil was soon christened ‘Lucy’ and you canread the exciting story of the find on the internet. ‘Lucy’ was so important because shehad the size and shape of a chimpanzee, but also had many characteristics of modernhumans.128
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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
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Chapter 2Reading landscapes: how la
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Figure 2.3: Rock fragments loosened
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Figure 2.6: The jo
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Figure 2.10: The m
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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
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
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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
Page 105 and 106: Figure 3.26: Global temperature cha
Page 107 and 108: Figure 3.29: A computer generated p
Page 109 and 110: Figure 3.31: The
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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 119 and 120: Figure 4.9: The ch
Page 121 and 122: Figure 4.12: The 4
Page 123 and 124: Millionsof years Some Major Earth E
Page 125 and 126: Figure 5.2: Strike-slip movement (r
Page 127 and 128: Figure 5.4: The So
Page 129 and 130: Figure 5.6: An ash eruption rising
Page 131 and 132: Figure 5.10: A hazard zone map of t
Page 133 and 134: isk to humans. The
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 145 and 146: Figure 5.22: A dinosaur reconstruct
Page 147 and 148: Figure 5.25: A working aggregate-pr
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Page 151 and 152: Chapter 6Understanding what geologi
Page 153 and 154: Figure 6.2: A drilling rig used for
Page 155 and 156: When an oil/gas field has been foun
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
Page 171 and 172: Evaporite deposits (or evaporites)
Page 173 and 174: Geophysical survey Using the method
Page 175 and 176: “Integrated waste management” <
Page 177 and 178: Metamorphism The r
Page 179 and 180: Pore spaces (or pores) Gaps bet<str
Page 181 and 182: Saltation Sediment movement by flui
Page 183 and 184: Suspension Sediment movement by flu
Page 185 and 186: AcknowledgementsPermission to repri
Page 187 and 188: Figure 2.3 A scree slope. Photo ID:
Page 189 and 190: Figure 1.15a Hematite.Figure 1.15b
Page 191 and 192: 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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