Historical Geology: Evolution of the Earth and Life Through Time

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Historical Geology Evolution of the Earth and
Life Through Time

• 6th edition
• Reed Wicander and James S. Monroe

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Chapter 1
The Dynamic and Evolving Earth
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The Movie of Earths History

• What kind of movie would we have
• if it were possible to travel back in time
• and film Earths history
• from its beginning 4.6 billion years ago?
• It would certainly be a story of epic proportions
• with incredible special effects
• a cast of trillions
• a plot with twists and turns
• and an ending that is still a mystery!
• Although we cannot travel back in time,
• the Earths history is still preserved
• in the geologic record

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Subplot Landscape History

• In this movie we would see
• a planet undergoing remarkable change as
• continents moved about its surface
• ocean basins opened and closed
• mountain ranges formed along continental margins
  or where continents collided
• The oceans and atmospheric circulation patterns
  would
• shift in response to moving continents
• causing massive ice sheets to form, grow, and
  then melt away
• Extensive swamps or vast interior deserts
• would sweep across the landscape

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Subplot Lifes 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.

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Earth is a Dynamic and Evolving Planet
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At the End of the Movie

• The movies final image is of Earth,
• a shimmering blue-green oasis
• in the black void of space
• and a voice-over says,
• To be continued.

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The Movies Theme

• Every good movie has a theme,
• and The History of Earth is no exception.
• The major theme is that Earth is complex and
  dynamic
• Three interrelated themes sub-themes run
  throughout this epic
• The first is that Earths outermost part
• is composed of a series of moving plates
• Plate tectonics
• whose interactions have affected its physical and
  biological history.

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The Movies Theme

• The second is that Earths biota
• has evolved or changed throughout its history
• Organic evolution
• The third is that physical and biological changes
  
• have occurred over long periods of time
• Geologic or Deep Time
• Three interrelated themes
• are central to our understanding and appreciation
• of our planets history.

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Earth is a System of Interconnected Subsystems

• Atmosphere (air and gases)
• Hydrosphere (water and oceans)
• Biosphere (plants and animals)
• Lithosphere (Earths rocky surface)
• Mantle
• Core

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Interactions in Earths Subsystems

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This course is about historical geologyWhat is
Geology?

• From the Greek
• geo (Earth) logos (reason)
• Geology is the study of Earth
• Physical geology studies Earth materials,
• such as minerals and rocks
• as well as the processes operating within Earth
  and on its surface

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Historical Geology

• In historical geology we study
• changes in our dynamic planet
• how and why past events happened
• implication for todays global ecosystems
• Principles of historical geology
• not only aid in interpreting Earths history
• but also have practical applications
• William Smith, an English surveyor/engineer
• used his study of rock sequences and fossils
• to predict the kinds and thicknesses of rocks
• to be excavated in the construction of canals

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Scientific Method

• The scientific method
• an orderly and logical approach
• involves gathering and analyzing facts or data
• A hypothesis
• is a tentative explanation
• to explain observed phenomena
• Scientists make predictions using hypotheses
• then they test the predictions
• After repeated tests,
• if one hypothesis continues to explain the
  phenomena,
• scientists propose it as a theory

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Formulation of Theories

• Theory

• colloquial usage speculation or conjecture
• scientific usage
• coherent explanation for one or several related
  natural phenomena
• supported by a large body of objective evidence

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Origin of the Universe

• The Big Bang
• occurred approximately 14 billion years ago
• is a model for the evolution of the universe

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Evidence for the Big Bang

• Universe is expanding
• Galaxies are receding from each other, and
  produce a red spectral shift
• Doppler Effect

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Evidence for the Big Bang

• Universe is expanding
• Pervasive background radiation of 2.7 Kelvin
  above absolute zero
• the afterglow of the Big Bang

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Evidence for the Big Bang

• How do we determine the age of the universe?
• measure the rate of expansion
• backtrack to a time when the galaxies were all
  together at a single point

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Big Bang Model

• When the universe began
• All matter and energy were compressed
• infinitely small high-temperature and
  high-density state
• Time and space were set at zero
• During 1st second
• The four basic forces separated
• gravity, electromagnetic force, strong nuclear
  force, weak nuclear force
• Enormous expansion occurred

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Big Bang Model, continued

• After 30 minutes, nuclear reactions had
  completely ended
• The universes mass consisted of almost entirely
  hydrogen and helium nuclei
• Continued expansion and cooling produced stars
  and galaxies
• The composition of the universe changed
• Heavier elements are formed during stars deaths

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Features of Our Solar System

• Part of the Milky Way Galaxy
• Sun
• 8 planets
• one dwarf planet, Pluto
• 153 known moons (satellites)
• a tremendous number of asteroids
• most orbit the Sun between the orbits of Mars and
  Jupiter
• millions of comets and meteorites
• interplanetary dust and gases

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Relative Sizes of the Sun and Planets
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Solar System Configuration
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Origin of Our Solar System

• Solar nebula theory

• cloud of gases and dust

• formed a rotating disk
• concentrated 90 of material in center part of
  disk

• forming solar nebula
• with an embryonic Sun
• surrounded by a rotating cloud

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Embryonic Sun and Rotating Cloud

• Planetesimals formed
• and collided and grew in size and mass

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The Planets

• Terrestrial Planets
• Mercury
• Venus
• Earth
• Mars
• small, composed of rock and metallic elements

• Jovian Planets
• Jupiter
• Saturn
• Uranus
• Neptune
• large, composed of hydrogen, helium, ammonia,
  methane condense at low temperatures

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Earths Very Early History

• About 4.6 billion years ago, early Earth was
  probably
• cool
• with uniform composition/density
• Composed mostly of silicates, and
• iron and magnesium oxides
• The temperature increased because of
• meteorite impacts
• gravitational compression
• radioactive decay
• Iron and nickel melted and Earths homogeneous
  composition disappeared

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Earths Differentiation

• Differentiation segregated into a series of
  concentric layers of differing composition and
  density

• Molten iron and nickel sank to form the core

• Lighter silicates flowed up to form mantle and
  crust

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EarthDynamic Planet

• Earth is a dynamic planet
• The size, shape, and geographic distribution
• of continents and ocean basins have changed
  through time
• The composition of the atmosphere has evolved
• Life-forms existing today differ from those that
  lived in the past

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Earths Interior Layers

• Crust
• Continental (20-90 km thick)
• Oceanic (5-10 km thick)

• Mantle
• 83 volume
• composed largely of peridotite
• dark, dense igneous rock, rich in iron and
  magnesium

• Core
• Solid inner region, liquid outer region
• iron and a small amount of nickel

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Earths Interior Layers

• Lithosphere
• solid upper mantle and crust

• Crust
• Continental (20-90 km thick)
• Oceanic (5-10 km thick)

• Mantle
• 83 volume
• composed largely of peridotite
• dark, dense igneous rock, rich in iron and
  magnesium

• Asthenosphere
• part of upper mantle

• behaves plastically and slowly flows

• Core
• Solid inner region, liquid outer region
• iron and a small amount of nickel

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Earths Interior Layers

• Lithosphere
• solid upper mantle and crust

• broken into plates that move over the
  asthenosphere

• Asthenosphere
• part of upper mantle
• behaves plastically and slowly flows

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Earths Crust

• outermost layer
• continental (20-90 km thick)

• density 2.7 g/cm3
• contains Si, Al
• oceanic (5-10 km thick)

• density 3.0 g/cm3
• composed of basalt and gabbro

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Plate Tectonic Theory

• Lithosphere is broken into individual pieces or
  plates

• Plates move over the asthenosphere
• as a result of underlying convection cells

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Modern Plate Map
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Plate Tectonic Theory

• Plate boundaries are marked by
• Volcanic activity
• Earthquake activity
• At plate boundaries
• plates diverge,
• plates converge,
• plates slide sideways past each other

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Plate Tectonic Theory

• Types of plate boundaries

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Plate Tectonic Theory

• Influence on geological sciences
• Revolutionary concept
• major milestone, comparable to Darwins theory of
  evolution in biology
• Provides a framework for
• interpreting many aspects of Earth on a global
  scale
• relating many seemingly unrelated phenomena
• interpreting Earth history

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Plate Tectonics and Earth Systems

• Plate tectonics is driven by convection
• in the mantle
• and in turn drives mountain building
• and associated igneous and metamorphic activity

Solid Earth
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
Atmosphere
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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

Hydrosphere
Movement of continents creates corridors or
barriers to migration, the creation of
ecological niches, and transport of habitats
into more or less favorable climates
Biosphere
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Theory of Organic Evolution

• Provides a framework
• for understanding the history of life
• Charles Darwins
• On the Origin of Species by Means of Natural
  Selection, published in 1859,
• revolutionized biology

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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

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History of Life

• The fossil record 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

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Geologic Time

• From the human perspective, time units are
• seconds, hours, days, years
• Ancient human history
• hundreds or thousands of years ago
• Geologic history
• millions, hundreds of millions, billions of years

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Geologic Time Scale

• Resulted from the work of many 19th century
  geologists who
• gathered information
• from numerous rock exposures, and
• constructed a sequential chronology
• based on changes in Earths biota through time
• Ages subsequently were assigned to the time scale
• using radiometric dating techniques

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Geologic Time Scale
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Uniformitarianism

• Uniformitarianism is a cornerstone of geology
• 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 through time

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How Does the Study of Historical Geology Benefit
Us?

• Survival of the human species
• depends on understanding
• how Earths various subsystems
• work and interact
• By studying what has happened in the past
• on a global scale,
• and try to determine how our actions
• might affect the balance of subsystems in the
  future

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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

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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
• proposing theories
• Universe began with
• a Big Bang 14 billion years ago

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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
• Earth is differentiated into layers
• the oceanic and continental crust, mantle and
  core,
• with the upper mantle and crust
• making up the solid lithosphere
• which overlie the plastic asthenosphere

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Summary

• 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 formation of mountain ranges
• 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 Earths evolution

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Summary

• Uniformitarianism holds that the laws
• of nature have been constant through time
• Geology is an integral part of our lives
• and our standard of living depends
• on our use of natural resources
• that formed over millions and billions of years