Transcript Historical Geology

Historical Geology:
Evolution of the Earth and Life Through Time
6th edition
Reed Wicander and James S. Monroe
Chapter 1
The Dynamic and
Evolving Earth
The Movie of Earth’s History
• What kind of movie would we have
– 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
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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 Earth’s history is still preserved
– in the geologic record
Subplot: Landscape History
• In this movie we would see
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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
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-over says,
• “To be continued.”
The Movie’s 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 Earth’s outermost part
– is composed of a series of moving plates
• Plate tectonics
– whose interactions have affected its physical and
biological history.
The Movie’s Theme
• The second is that Earth’s 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 planet’s history.
Earth is a System of
Interconnected Subsystems
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Atmosphere (air and gases)
Hydrosphere (water and oceans)
Biosphere (plants and animals)
Lithosphere (Earth’s rocky surface)
Mantle
Core
Interactions in Earth’s
Subsystems
This course is about historical geology
What 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
Historical Geology
• In historical geology we study
– changes in our dynamic planet
– how and why past events happened
– implication for today’s global ecosystems
• Principles of historical geology
– not only aid in interpreting Earth’s 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
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
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
Origin of the Universe
• The Big Bang
– occurred approximately 14 billion years ago
– is a model for the evolution of the universe
Evidence for the Big Bang
• Universe is expanding
– Galaxies are receding from each other, and
produce a red spectral shift
• Doppler Effect
Evidence for the Big Bang
• Universe is expanding
• Pervasive background radiation of 2.7
Kelvin above absolute zero
– the afterglow of the Big Bang
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
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
Big Bang Model, continued
• After 30 minutes, nuclear reactions had
completely ended
• The universe’s 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
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
Relative Sizes of the
Sun and Planets
Solar System Configuration
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
Embryonic Sun and Rotating Cloud
• Planetesimals formed
– and collided and grew in size and mass
The Planets
• Terrestrial Planets
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Mercury
Venus
Earth
Mars
• small, composed of
rock and metallic
elements
• Jovian Planets
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Jupiter
Saturn
Uranus
Neptune
• large, composed of
hydrogen, helium,
ammonia, methane;
condense at low
temperatures
Earth’s Very Early History
• About 4.6 billion years ago, early Earth was
probably
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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 Earth’s homogeneous
composition disappeared
Earth’s 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
Earth—Dynamic 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
Earth’s 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
Earth’s Interior Layers
• Crust
– Continental (20-90 km
thick)
– Oceanic (5-10 km thick)
• Lithosphere
– solid upper mantle
and crust
• 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
• Asthenosphere
– part of upper
mantle
– behaves plastically
and slowly flows
Earth’s 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
Earth’s 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
Plate Tectonic Theory
• Lithosphere is broken into individual pieces or
plates
• Plates move over the asthenosphere
– as a result of underlying convection cells
Modern Plate Map
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
Plate Tectonic Theory
• Types of plate boundaries
Plate Tectonic Theory
Influence on geological sciences:
• Revolutionary concept
– major milestone, comparable to Darwin’s 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
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
• Charles 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 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
– seconds, hours, days, years
• Ancient human history
– hundreds or thousands of years ago
• Geologic history
– millions, hundreds of millions, billions of years
Geologic Time Scale
• Resulted from the work of many 19th century
geologists who
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gathered information
from numerous rock exposures, and
constructed a sequential chronology
based on changes in Earth’s biota through time
• Ages subsequently were assigned to the time
scale
– using radiometric dating techniques
Geologic
Time Scale
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
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
• 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
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
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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
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
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 Earth’s evolution
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