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Title: Historical Geology: Evolution of the Earth and Life Through Time


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

2
Chapter 1
The Dynamic and Evolving Earth
3
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

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 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.

6
Earth is a Dynamic and Evolving Planet
7
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.

8
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.

9
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
  • These three interrelated themes
  • are central to our understanding and appreciation
  • of our planets history.

10
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

11
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

12
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

13
Chapter 4
Geologic TimeConcepts and Principles
14
Grand Canyon
  • When looking down into the Grand Canyon, we are
    really looking at the early history of Earth

15
Grand Canyon
  • More than 1 billion years of history are
    preserved,
  • like pages of a book,
  • in the rock layers of the Grand Canyon
  • Reading this rock book we learn
  • that the area underwent episodes of
  • mountain building
  • advancing and retreating shallow seas
  • We know these things by
  • applying the principles of relative dating to the
    rocks
  • and recognizing that present-day processes
  • have operated throughout Earth history

16
What is time?
  • We are obsessed with time, and organize our lives
    around it.
  • Most of us feel we dont have enough of it.
  • Our common time units are
  • seconds
  • hours
  • days
  • weeks
  • months
  • years
  • Ancient history involves
  • hundreds of years
  • thousands of years
  • But geologic time involves
  • millions of years
  • even billions of years

17
Concept of Geologic Time
  • Geologists use two different frames of reference
  • when discussing geologic time
  • Relative dating involves placing geologic events
  • in a sequential order as determined
  • from their position in the geologic record
  • It does not tell us how long ago
  • a particular event occurred,
  • only that one event preceded another
  • For hundreds of years geologists
  • have been using relative dating
  • to establish a relative geologic time scale

18
Relative Geologic Time Scale
  • The relative geologic time scale has a sequence
    of
  • eons
  • eras
  • periods
  • epochs

19
Concept of Geologic Time
  • The second frame of reference for geologic time
  • is absolute dating
  • Absolute dating results in specific dates
  • for rock units or events
  • expressed in years before the present
  • It tells us how long ago a particular event
    occurred
  • giving us numerical information about time
  • Radiometric dating is the most common method
  • of obtaining absolute ages
  • Such dates are calculated
  • from the natural rates of decay
  • of various natural radioactive elements
  • present in trace amounts in some rocks

20
Geologic Time Scale
  • The discovery of radioactivity
  • near the end of the 19th century
  • allowed absolute ages
  • to be accurately applied
  • to the relative geologic time scale
  • The geologic time scale is a dual scale
  • a relative scale
  • and an absolute scale

21
Changes in the Concept of Geologic Time
  • The concept and measurement of geologic time
  • have changed throughout human history
  • Early Christian theologians
  • conceived of time as linear rather than circular
  • James Ussher (1581-1665) in Ireland
  • calculated the age of Earth based
  • on Old Testament genealogy
  • He announced that Earth was created on October
    22, 4004 B.C.
  • For nearly a century, it was considered heresy to
    say Earth was more than about 6000 years old.

22
Changes in the Concept of Geologic Time
  • During the 1700s and 1800s Earths age
  • was estimated scientifically
  • Georges Louis de Buffon (1707-1788)
  • calculated how long Earth took to cool gradually
  • from a molten beginning
  • using melted iron balls of various diameters.
  • Extrapolating their cooling rate
  • to an Earth-sized ball,
  • he estimated Earth was 75,000 years old

23
Changes in the Concept of Geologic Time
  • Others used different techniques
  • Scholars using rates of deposition of various
    sediments
  • and total thickness of sedimentary rock in the
    crust
  • produced estimates of less than 1 million
  • to more than 2 billion years.
  • John Joly used the amount of salt carried
  • by rivers to the ocean
  • and the salinity of seawater
  • and obtained a minimum age of 90 million years

24
Relative-Dating Principles
  • Six fundamental geologic principles are used in
    relative dating
  • Principle of superposition
  • Nicolas Steno (1638-1686)
  • In an undisturbed succession of sedimentary rock
    layers,
  • the oldest layer is at the bottom
  • and the youngest layer is at the top
  • This method is used for determining the relative
    age
  • of rock layers (strata) and the fossils they
    contain

25
Relative-Dating Principles
  • Principle of original horizontality
  • Nicolas Steno
  • Sediment is deposited
  • in essentially horizontal layers
  • Therefore, a sequence of sedimentary rock layers
  • that is steeply inclined from horizontal
  • must have been tilted
  • after deposition and lithification

26
Principle of Superposition
  • Illustration of the principles of superposition
  • Superposition The youngest
  • rocks are at the top
  • of the outcrop
  • and the oldest rocks are at the bottom

27
Principle of Original
Horizontality
  • Horizontality These sediments were originally
  • deposited horizontally
  • in a marine environment

28
Relative-Dating Principles
  • Principle of lateral continuity
  • Nicolas Stenos third principle
  • Sediment extends laterally in all direction
  • until it thins and pinches out
  • or terminates against the edges
  • of the depositional basin
  • Principle of cross-cutting relationships
  • James Hutton (1726-1797)
  • An igneous intrusion or a fault
  • must be younger than the rocks
  • it intrudes or displaces

29
Cross-cutting Relationships
  • North shore of Lake Superior, Ontario Canada
  • A dark-colored dike has intruded into older light
    colored granite.
  • The dike is younger than the granite.

30
Cross-cutting Relationships
  • Templin Highway, Castaic, California
  • A small fault displaces tilted beds.
  • The fault is younger than the beds.

31
Relative-Dating Principles
  • Other principles of relative dating
  • Principle of inclusions
  • Principle of fossil succession
  • are discussed later in the text

32
Neptunism
  • Neptunism
  • All rocks, including granite and basalt,
  • were precipitated in an orderly sequence
  • from a primeval, worldwide ocean.
  • proposed in 1787 by Abraham Werner (1749-1817)
  • Werner was an excellent mineralogist,
  • but is best remembered
  • for his incorrect interpretation of Earth history

33
Neptunism
  • Werners geologic column was widely accepted
  • Alluvial rocks
  • unconsolidated sediments, youngest
  • Secondary rocks
  • rocks such as sandstones, limestones, coal,
    basalt
  • Transition rocks
  • chemical and detrital rocks, some fossiliferous
    rocks
  • Primitive rocks
  • oldest including igneous and metamorphic

34
Catastrophism
  • Catastrophism
  • concept proposed by Georges Cuvier (1769-1832)
  • dominated European geologic thinking
  • The physical and biological history of Earth
  • resulted from a series of sudden widespread
    catastrophes
  • which accounted for significant and rapid changes
    in Earth
  • and exterminated existing life in the affected
    area
  • Six major catastrophes occurred,
  • corresponding to the six days of biblical
    creation
  • The last one was the biblical deluge

35
Neptunism and Catastrophism
  • These hypotheses were abandoned because
  • they were not supported by field evidence
  • Basalt was shown to be of igneous origin
  • Volcanic rocks interbedded with sedimentary
  • and primitive rocks showed that igneous activity
  • had occurred throughout geologic time
  • More than 6 catastrophes were needed
  • to explain field observations
  • The principle of uniformitarianism
  • became the guiding philosophy of geology

36
Uniformitarianism
  • Principle of uniformitarianism
  • Present-day processes have operated throughout
    geologic time.
  • Developed by James Hutton (1726-1797), advocated
    by Charles Lyell (1797-1875)
  • William Whewell coined the term
    uniformitarianism in 1832
  • Hutton applied the principle of uniformitarianism
  • when interpreting rocks at Siccar Point, Scotland
  • We now call what Hutton observed an unconformity,
  • but he properly interpreted its formation

37
Unconformity at Siccar Point
  • Hutton explained that
  • the tilted, lower rocks
  • resulted from severe upheavals that formed
    mountains
  • these were then worn away
  • and covered by younger flat-lying rocks
  • the erosional surface
  • represents a gap in the rock record

38
Uniformitarianism
erosion
erosion
  • Hutton viewed Earth history as cyclical

deposition
uplift
  • He also understood
  • that geologic processes operate over a vast
    amount of time
  • Modern view of uniformitarianism
  • Today, geologists assume that the principles or
    laws of nature are constant
  • but the rates and intensities of change have
    varied through time
  • Some geologists prefer the term actualism

39
Crisis in Geology
  • Lord Kelvin (1824-1907)
  • knew about high temperatures inside of deep mines
  • and reasoned that Earth
  • was losing heat from its interior
  • Assuming Earth was once molten, he used
  • the melting temperature of rocks
  • the size of Earth
  • and the rate of heat loss
  • to calculate the age of Earth as
  • between 400 and 20 million years

40
Crisis in Geology
  • This age was too young
  • for the geologic processes envisioned
  • by other geologists at that time,
  • leading to a crisis in geology
  • Kelvin did not know about radioactivity
  • as a heat source within the Earth

41
Absolute-Dating Methods
  • The discovery of radioactivity
  • destroyed Kelvins argument for the age of Earth
  • and provided a clock to measure Earths age
  • Radioactivity is the spontaneous decay
  • of an element to a more stable isotope
  • The heat from radioactivity
  • helps explain why the Earth is still warm inside
  • Radioactivity provides geologists
  • with a powerful tool to measure
  • absolute ages of rocks and past geologic events

42
Atoms A Review
  • Understanding absolute dating requires
  • knowledge of atoms and isotopes
  • All matter is made up of atoms
  • The nucleus of an atom is composed of
  • protons particles with a positive electrical
    charge
  • neutrons electrically neutral particles
  • with electrons negatively charged particles
    outside the nucleus
  • The number of protons ( the atomic number)
  • helps determine the atoms chemical properties
  • and the element to which it belongs

43
Isotopes A Review
  • Atomic mass number
  • number of protons number of neutrons
  • The different forms of an elements atoms
  • with varying numbers of neutrons
  • are called isotopes
  • Different isotopes of the same element
  • have different atomic mass numbers
  • but behave the same chemically
  • Most isotopes are stable,
  • but some are unstable
  • Geologists use decay rates of unstable isotopes
  • to determine absolute ages of rocks

44
Radioactive Decay
  • Radioactive decay is the process whereby
  • an unstable atomic nucleus spontaneously
    transforms
  • into an atomic nucleus of a different element

45
Half-Lives
  • The half-life of a radioactive isotope
  • is the time it takes for
  • one half of the atoms
  • of the original unstable parent isotope
  • to decay to atoms
  • of a new more stable daughter isotope
  • The half-life of a specific radioactive isotope
  • is constant and can be precisely measured

46
Half-Lives
  • The length of half-lives for different isotopes
  • of different elements
  • can vary from
  • less than one billionth of a second
  • to 49 billion years!
  • Radioactive decay
  • is geometric, NOT linear,
  • and produces a curved graph

47
Uniform Linear Change
  • In this example
  • of uniform linear change,
  • water is dripping into a glass
  • at a constant rate

48
Geometric Radioactive Decay
  • In radioactive decay,
  • during each equal time unit
  • half-life
  • the proportion of parent atoms
  • decreases by 1/2

49
Determining Age
  • By measuring the parent/daughter ratio
  • and knowing the half-life of the parent
  • which has been determined in the laboratory
  • geologists can calculate the age of a sample
  • containing the radioactive element
  • The parent/daughter ratio
  • is usually determined by a mass spectrometer
  • an instrument that measures the proportions
  • of atoms with different masses

50
Determining Age
  • Example
  • If a rock has a parent/daughter ratio of 13
  • or a ratio of (parent)/(parent daughter) 14
    or 25,
  • and the half-live is 57 million years,
  • how old is the rock?
  • 25 means it is 2 half-lives old.
  • the rock is 57my x 2 114 million years old.

51
What Materials Can Be Dated?
  • Most radiometric dates are obtained
  • from igneous rocks
  • As magma cools and crystallizes,
  • radioactive parent atoms separate
  • from previously formed daughter atoms
  • Because they are the right size
  • some radioactive parents
  • are included in the crystal structure of cooling
    minerals

52
What Materials Can Be Dated?
  • The daughter atoms are different elements
  • with different sizes
  • and, therefore, do not generally fit
  • into the same minerals as the parents
  • Geologists can use the crystals containing
  • the parent atoms
  • to date the time of crystallization

53
Igneous Crystallization
  • Crystallization of magma separates parent atoms
  • from previously formed daughters
  • This resets the radiometric clock to zero.
  • Then the parents gradually decay.

54
Sedimentary Rocks
  • Generally, sedimentary rocks can NOT be
    radiometrically dated
  • The date obtained would correspond to the time of
    crystallization of the mineral,
  • when it formed in an igneous or metamorphic rock,
  • and NOT the time that it was deposited as a
    sedimentary particle
  • Exception The mineral glauconite can be dated
  • because it forms in certain marine environments
    as a reaction with clay minerals
  • during the formation of the sedimentary rock

55
Dating Metamorphism
  • a. A mineral has just crystallized from magma.

b. As time passes, parent atoms decay to
daughters.
c. Metamorphism drives the daughters out of the
mineral as it recrystallizes.
d. Dating the mineral today yields a date of 350
million years time of metamorphism, provided
the system remains closed during that time.
Dating the whole rock yields a date of 700
million years time of crystallization.
56
Long-Lived Radioactive Isotope Pairs Used in
Dating
  • The isotopes used in radiometric dating
  • need to be sufficiently long-lived
  • so the amount of parent material left is
    measurable
  • Such isotopes include
  • Parents Daughters Half-Life (years)

Most of these are useful for dating older rocks
Uranium 238 Lead 206 4.5 billion Uranium
234 Lead 207 704 million Thorium 232
Lead 208 14 billion Rubidium 87 Strontium
87 48.8 billion Potassium 40 Argon 40 1.3
billion
57
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

58
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

59
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

60
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

61
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

62
Geologic Time Scale
63
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

64
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

65
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

66
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

67
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

68
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

69
Plate Tectonic Theory
  • Lithosphere is broken into individual pieces or
    plates
  • Plates move over the asthenosphere
  • as a result of underlying convection cells

70
Modern Plate Map
71
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

72
Plate Tectonic Theory
  • Types of plate boundaries

73
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

74
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
75
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
76
Next time Chapter 3 Plate Tectonics
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