Text: Historical Geology

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Text Historical Geology

• Evolution of Earth and Life Through Time
• 4th edition
• by Wicander and 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 see
• 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 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 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
• ocean basins opened
• mountain ranges grew along continental margins
• and where continents collided
• The oceans and atmosphere would
• form and grow
• change circulation patterns
• cause massive ice sheets to form and 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 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
• Three interrelated themes run throughout it
• 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
• The second is that Earths biota
• has evolved or changed throughout its history
• organic evolution

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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)
• Interior (mantle and core)

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Interactions in Earths Subsystems
Gases from respiration Transport of seeds and
spores
Atmosphere Biosphere
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Interactions in Earths Subsystems
Wind erosion, transport of water vapor for
precipitation Mountainsdivert air movements
Atmosphere Lithosphere
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Interactions in Earths Subsystems
Source of sediment and dissolved material Water
and glacial erosion, solution of minerals
Hydrosphere Lithosphere
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This class 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
• and on Earths 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 study of rock sequences
• to help predict the difficulty of excavation
• in constructing canals

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Scientific Method

• The scientific method
• an orderly and logical approach
• Gather and analyze 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 15 billion years ago
• and is a model for the beginning of the universe

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Evidence for the Big Bang

• Universe is expanding
• How do we determine the age?
• measure the rate of expansion
• backtrack to a time when the galaxies
• were all together at a single point
• Pervasive background radiation of 2.7º above
  absolute zero
• is the afterglow of the Big Bang

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Big Bang Model

• Initial state
• No time, matter or space existed
• There is no before the Big Bang
• Universe consisted of pure energy
• During 1st second
• Very dense matter came into existence
• The four basic forces separated
• gravity, electromagnetic force, 2 nuclear forces
• Enormous expansion occurred

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Big Bang Model (cont.)

• 300,000 years later
• atoms of hydrogen and helium formed
• light (photons) burst forth for the first time
• During the next 200 million years
• Continued expansion and cooling
• Stars and galaxies began to form
• Elements heavier than hydrogen and helium
• began to form within stars by nuclear fusion

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Features of Our Solar System

• In a spiral arm of the Milky Way Galaxy
• Sun
• 9 planets
• 101 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
• condensed and collapsed due to gravity

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

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Embryonic Sun and Rotating Cloud

• Planetesimals have formed
• in the inner solar system,
• and large eddies of gas and dust
• remain far from the protosun

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The Planets

• Terrestrial Planets
• Mercury
• Venus
• Earth
• Mars
• small, composed of rock, with metal cores

• Jovian Planets
• Jupiter
• Saturn
• Uranus
• Neptune
• large, composed of hydrogen, helium, ammonia,
  methane, relatively small rocky cores

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Earths Very Early History

• Started out cool about 4.6 billion years ago
• probably with uniform composition/density
• Mostly
• silicate compounds
• iron and magnesium oxides
• Temperature increased. Heat sources
• meteorite impacts
• gravitational compression
• radioactive decay
• Heated up enough to melt iron and nickel

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Earths 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

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Forming the Earth-Moon System

• Impact by Mars-sized or larger planetesimal with
  young Earth
• 4.6 to 4.4 billion years ago

• ejected large quantity of hot material,

• and formed the Moon

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Forming the Earth-Moon System

• Most of the lunar material
• came from the mantle of the colliding
  planetesimal
• The material cooled
• and crystallized
• into lunar layers

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Forming the Earth-Moon System

• Most of the lunar material
• came from the mantle of the colliding
  planetesimal
• The material cooled
• and crystallized
• into lunar layers

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Moon

• Light-colored areas are lunar highlands

• Heavily cratered
• Provide striking evidence
• of massive meteorite bombardment

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EarthDynamic Planet

• Earth was also subjected
• to the same meteorite barrage
• that pock-marked the Moon
• Why isnt Earths surface also densely cratered?
• Because Earth is a dynamic and evolving planet
• Craters have long since been worn away

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Earths Interior Layers

• Crust - 5-90 km thick
• continental and oceanic

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

• Core
• iron and a small amount of nickel

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Earths Interior Layers

• Lithosphere
• solid upper mantle and crust

• Crust - 5-90 km thick
• continental and oceanic

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

• Asthenosphere
• part of upper mantle

• behaves plastically and slowly flows

• Core
• 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

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Plate Tectonic Theory

• Lithosphere is broken into individual pieces
  called 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

• At plate boundaries
• Volcanic activity occurs
• Earthquakes occur
• Movement at plate boundaries
• plates diverge
• plates converge
• plates slide sideways past each other

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Plate Tectonic Theory

• Types of plate boundaries

Transform plate boundary
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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
• 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 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

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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

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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 Earths biota through time
• The time scale was subsequently dated in years
• using radiometric dating techniques

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Geologic Time Scale
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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

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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
• 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

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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 and theories
• Universe began with
• a big bang 15 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
• 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

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Summary

• Earths 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

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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 Earths 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