Module 13 - Historical Geology.pdf - Module 24 Historical...

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Unformatted text preview: Module 24 Historical Geology EARTH’S VERY EARLY HISTORY About 4.6 billion years ago . . . • The Earth started out cool • Probably with uniform composition/density mostly silicate compounds iron and magnesium oxides • Temperature increased with heat sources: – meteorite impacts – gravitational compression – radioactive decay • Heated up enough to melt iron and nickel EARTH’S VERY EARLY HISTORY Earth’s differentiation • Differentiation = segregated into layers of differing composition and density • Early Earth was probably uniform • Molten iron and nickel sank to form the core • Lighter silicates flowed up to form mantle and crust EARTH’S VERY EARLY HISTORY Forming the Earth-Moon system • 4.6 to 4.4 billion years ago • the young Earth was impacted by Marssized or larger planetesimal • ejected large quantity of hot material • and . . . formed the Moon EARTH’S VERY EARLY HISTORY Forming the Earth-Moon system EARTH’S VERY EARLY HISTORY Moon • Most of the lunar material came from the mantle of the colliding planetesimal • The material cooled and crystallized into lunar layers EARTH’S VERY EARLY HISTORY Moon • Light-colored areas are lunar highlands • Heavily cratered provide striking evidence of massive meteorite bombardment EARTH’S VERY EARLY HISTORY Earth ‰ ‰ ‰ ‰ Atmosphere Hydrosphere CMC-sphere Biosphere EARTH’S VERY EARLY HISTORY CMC-sphere CRUST ¾ continental-crust: granitic (sialic) composition ¾ oceanic-crust: basaltic (mafic) composition MANTEL ¾ composed largely of peridotite ¾ dark, dense igneous rock ¾ rich in iron and magnesium CORE ¾ composed largely of iron and a small amount of nickel 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 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 Geologic Time Scale GEOLOGIC TIME Geologic Time Scale and football field The history of plate movement 150 million years ago 100 million years ago 60 million years ago 30 million years ago 5 million years ago The history of plate movement during the last 200 million years has been reconstructed from all available geologic and geophysical data. These maps show the general directions of movement from the time Pangaea began to break up until the continents moved to their present positions The history of organism SUMMARY • Universe began with – a big bang 15 billion years ago • 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 • 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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  • Fall '19
  • Mantle, Uniformitarianism, 5 million years

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