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Text: Historical Geology Evolution of Earth and Life Through Time 4th edition by Wicander and Monroe Chapter The Dynamic and Evolving Earth The Movie of Earth’s History • What kind of movie would we see – if it were possible to travel back in time – and film Earth’s History – from its beginning 4.6 billion years ago? • It would certainly be a story of epic proportions – – – – with great special effect and a cast of trillions twists and turns in its plot with an unknown ending • Although we cannot travel back in time, – the Earth’s History is still preserved – in the geologic record Subplot: Landscape History • In this movie we would see – – – – – a planet undergoing remarkable change as continents moved about ocean basins opened mountain ranges grew along continental margins and where continents collided – – – – form and grow change circulation patterns cause massive ice sheets to form and grow and then melt away • The oceans and atmosphere would • Extensive swamps or vast interior deserts – would sweep across the landscape Subplot: Life’s History • We would also witness – the first living cells evolving – from a primordial organic soup – between 4.6 and 3.6 billion years ago • Cell nuclei would evolve, – then multicelled soft-bodied animals – followed by animals with skeletons and then backbones • The barren landscape would come to life as – plants and animals moved from their watery home – insects, amphibians, reptiles, birds and mammals – would eventually evolve Earth is a Dynamic and Evolving Planet • Changes in its surface • Changes in life At the End of the Movie • The movie’s final image is of Earth, – a shimmering blue-green oasis – in the black void of space – and a voice says, • “To be continued.” The Movie’s Theme • Every good movie has a theme, – and “The History of Earth” is no exception • Three interrelated themes run throughout it • The first is that Earth’s outermost part – is composed of a series of moving plates • Plate tectonics – whose interactions have affected its physical and biological history • The second is that Earth’s biota – has evolved or changed throughout its history • organic evolution Earth is a System of Interconnected Subsystems • • • • • Atmosphere (air and gases) Hydrosphere (water and oceans) Biosphere (plants and animals) Lithosphere (Earth’s rocky surface) Interior (mantle and core) Interactions in Earth’s Subsystems re e h p s o e r m e t h A p s Bio Gases from respiration Transport of seeds and spores Solid Earth Plate tectonics is driven by convection in the mantle and in turn drives mountain building and associated igneous and metamorphic activity Atmosphere Plate Tectonics and Earth Systems Arrangement of continents affects solar heating and cooling, and thus winds and weather systems Rapid plate spreading and hot-spot activity may release volcanic carbon dioxide and affect global climate Biosphere Hydrosphere Plate Tectonics and Earth Systems Continental arrangement affects ocean currents Rate of spreading affects volume of mid-oceanic ridges and hence sea level Placement of continents may contribute to the onset of ice ages Movement of continents creates corridors or barriers to migration, the creation of ecological niches, and transport of habitats into more or less favorable climates Theory of Organic Evolution • Provides a framework – for understanding the history of life • Darwin’s – On the Origin of Species by Means of Natural Selection, published in 1859, – revolutionized biology Central Thesis of Evolution • All present-day organisms – are related – and descended from organisms – that lived during the past • Natural selection is the mechanism – that accounts for evolution • Natural selection results in the survival – to reproductive age of those organisms – best adapted to their environment History of Life • The fossil record provides perhaps – the most compelling evidence – in favor of evolution • Fossils are the remains or traces – of once-living organisms • Fossils demonstrate that Earth – has a history of life Geologic Time • From the human perspective time units are in – seconds, hours, days, years • Ancient human history – hundreds or even thousands of years • Geologic history – millions, hundreds of millions, billions of years Geologic Time Scale • Resulted from the work of many 19th century geologists who – – – – pieced together information from numerous rock exposures, constructed a sequential chronology based on changes in Earth’s biota through time • The time scale was subsequently dated in years – using radiometric dating techniques Geologic Time Scale Uniformitarianism • Uniformitarianism is a cornerstone of geology – is based on the premise that present-day processes – have operated throughout geologic time • The physical and chemical laws of nature – have remained the same through time • To interpret geologic events – from evidence preserved in rocks – we must first understand present-day processes – and their results • Rates and intensities of geologic processes – may have changed with time How Does the Study of Historical Geology Benefit Us? • Survival of the human species – depends on understanding – how Earth’s various subsystems – work and interact • Study what has happened in the past, – on a global scale, – to try and determine how our actions – might affect the balance of subsystems in the future We “Live” Geology • Our standard of living depends directly on – our consumption of natural resources – resources that formed millions and billions of years ago • How we consume natural resources – and interact with the environment determines – our ability to pass on this standard of living – to the next generation Summary • Earth is a system – of interconnected subsystems • Geology is the study of Earth • Historical geology is the study – of the origin and evolution of Earth • Scientific method is – – – – an orderly, logical approach to explain phenomena, using data, formulating and testing hypotheses and theories • Universe began with – a big bang 15 billion years ago Summary • Solar system formed 4.6 billion years ago – by condensation and gravitational collapse – of a rotating interstellar cloud • Earth formed 4.6 billion years ago – as a swirling eddy in the solar system nebula • Moon may have formed – when a planetesimal collided with Earth – 4.6 to 4.4 billion years ago • Earth probably started solid – then differentiated into layers – as it heated and melted Summary • Earth’s layers mostly solidified – – – – into the core, mantle and crust, with the upper mantle and crust making up the soft asthenosphere and the solid lithosphere • Lithosphere is broken into plates – that diverge, converge and – slide sideways past each other • Plate tectonics is a unifying theory – that helps explain features and events – including volcanic eruptions, – earthquakes and mountain forming Summary • Central thesis of organic evolution is – that all living organisms evolved – from organisms that existed in the past • An appreciation – of the immensity of geologic time – is central to understanding Earth’s evolution • Uniformitarianism holds that the laws – of nature have been constant through time • Geology is part of our lives – and our standard of living depends – on our use of natural resources – that formed over billions of years
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