Text: Historical Geology
Evolution of Earth and Life Through Time
4th edition
by Wicander and Monroe
Chapter 1
The Dynamic and Evolving Earth
…a brief overview of the semester….refresher
from last semester….
-Big Bang origin of universe!
-the Scientific Method
-Geologic Time
-Evolution
-Plate Tectonics
- Summary of development of Life through Geologic Time….
trilobites to dinosaurs to birds to horses to apes to Modern Man…
Historical Geology
• Learn to tell time using different clock..
– The Geologic Time Scale…
• View geology in 3 dimensions.
• Focus on semester, last ¾ , will be on changes in
both the surface of Earth and life that existed on 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
This class 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
– and on Earth’s 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 study of rock sequences
– to help predict the difficulty of excavation
– in constructing canals
Scientific Method
• The scientific method
– an orderly and logical approach
– Gather and analyze facts or data
• 1. A hypothesis is a tentative explanation
– to explain observed phenomena
– 2. Gather and analyze facts or data
• Scientists make predictions using hypotheses
-3. then they test the predictions
• After repeated tests, make 4. Conclusion
– if one hypothesis continues
– to explain the phenomena,
– scientists propose it as a theory
Origin of the Universe
• The Big Bang
– occurred 15 billion years ago
– and is a model for the beginning of the universe
– Age of Earth: 4.5 Billion years
Solar System Configuration
Houston Chronicle- August 16, 2006
Earth’s 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
Plate Tectonic Theory
• Lithosphere is broken into individual pieces
called
plates
• Plates move over the asthenosphere
– as a result of underlying convection cells
Modern Plate Map
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 Scale
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
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
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
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 Interior Layers
• Crust - 5-90 km
thick
– continental and
oceanic
• Lithosphere
– solid upper mantle
and crust
• Mantle
– composed largely
of peridotite
– dark, dense
igneous rock
– rich in iron and
magnesium
• Core
– 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
– granite
• oceanic (5-10 km thick)
– density 3.0 g/cm3
– composed of basalt
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
Plate Tectonic Theory
• Types of plate boundaries
Divergent
Mid-oceanic plate
ridge
boundary
Transform
plate
boundary
Continentalcontinental
convergent
plate
boundary
Continentaloceanic
convergent
plate
boundary
Divergent
plate
boundary
Trench
Oceanicoceanic
convergent
plate
boundary
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
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
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
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
Principle of Horizontality
• Illustration of the principles of superposition
– and original horizontality
• Horizontality: These sediments
were originally
– deposited horizontally
– in a marine environment
– This outcrop is Chattanooga Shale, Tennessee
Principle of Superposition
• Illustration of the principles of superposition
– and original horizontality
• Superposition: The youngest
– rocks are at the top
– of the outcrop
– and the oldest rocks are at the bottom
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
• Recent events in Indian Ocean area and southern
California demonstrate that…..
• 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’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
Text: Historical Geology
Evolution of Earth and Life Through Time
4th edition
by Wicander and Monroe
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.”
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
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
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
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
Relative Sizes of the
Sun and Planets