1. Historical Geology: Evolution of the Earth and Life Through Time
6th edition
Reed Wicander and James S. Monroe

2. The Dynamic and Evolving Earth
Chapter 1
The Dynamic and Evolving Earth

3. 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
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

4. 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

5. 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.

6. Earth is a Dynamic and Evolving Planet
Changes in its surface
Changes in life
Images from left to right:
Changes in its surface
Artist’s rendition of how Earth is thought to have appeared about 4.6 billion years ago.
Paleogeography of the world for the Late Cambrian Period.
Apollo 17 view of Earth. Africa, Arabian Peninsula, Madagascar, Antarctica, South Atlantic Ocean , Indian Ocean.
Changes in life
Possible precursor of life: bacterium-like proteinoid.
Reconstruction of Middle Devonian reef from the Great Lakes area Shown are corals, ammonoids, trilobites and brachiopods.
Cretaceous Pteranodon.

7. 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.”

8. 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.

9. 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.

10. Earth is a System of Interconnected Subsystems
Atmosphere (air and gases)
Hydrosphere (water and oceans)
Biosphere (plants and animals)
Lithosphere (Earth’s rocky surface)
Mantle
Core

11. Interactions in Earth’s Subsystems

12. 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

13. 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

14. Scientific Method The scientific method A hypothesis
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

15. 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

16. Origin of the Universe The Big Bang
occurred approximately 14 billion years ago
is a model for the evolution of the universe

17. Evidence for the Big Bang
Universe is expanding
Galaxies are receding from each other, and produce a red spectral shift
Doppler Effect

18. Evidence for the Big Bang
Universe is expanding
Pervasive background radiation of 2.7 Kelvin above absolute zero
the afterglow of the Big Bang

19. 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

20. Big Bang Model When the universe began During 1st second:
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

21. 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

22. 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

23. Relative Sizes of the Sun and Planets

24. Solar System Configuration

25. 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

26. Embryonic Sun and Rotating Cloud
Planetesimals formed
and collided and grew in size and mass

27. 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

28. Earth’s 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 Earth’s homogeneous composition disappeared

29. 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

30. 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

31. 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

32. Earth’s 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

33. 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

34. 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

35. Plate Tectonic Theory
Lithosphere is broken into individual pieces or plates
Plates move over the asthenosphere
as a result of underlying convection cells

36. Modern Plate Map

37. 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

38. Plate Tectonic Theory
Types of plate boundaries

39. 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

40. 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

41. 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

42. 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

43. 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

44. 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

45. 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

46. 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 Earth’s biota through time
Ages subsequently were assigned to the time scale
using radiometric dating techniques

47. Geologic Time Scale

48. 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

49. 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

50. 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

51. Summary Earth is a system Geology is the study of Earth
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

52. 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

53. 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

54. 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