Historical Geology: Evolution of the Earth and Life Through Time

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Historical Geology Evolution of the Earth and
Life Through Time

• 6th edition
• Reed Wicander and James S. 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 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

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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

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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-over 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.
• 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.

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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.

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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

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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

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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

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Chapter 4
Geologic TimeConcepts and Principles
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Grand Canyon

• When looking down into the Grand Canyon, we are
  really looking at the early history of Earth

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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

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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

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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

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Relative Geologic Time Scale

• The relative geologic time scale has a sequence
  of
• eons
• eras
• periods
• epochs

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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

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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

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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.

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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

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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

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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

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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

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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

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Principle of Original
Horizontality

• Horizontality These sediments were originally
• deposited horizontally
• in a marine environment

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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

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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.

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Cross-cutting Relationships

• Templin Highway, Castaic, California
• A small fault displaces tilted beds.

• The fault is younger than the beds.

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Relative-Dating Principles

• Other principles of relative dating
• Principle of inclusions
• Principle of fossil succession
• are discussed later in the text

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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

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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

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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

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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

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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

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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

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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

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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

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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

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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

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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

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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

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Radioactive Decay

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

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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

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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

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Uniform Linear Change

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

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Geometric Radioactive Decay

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

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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

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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.

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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

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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

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Igneous Crystallization

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

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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

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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.
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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
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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

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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 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
• seconds, hours, days, years
• Ancient human history
• hundreds or thousands of years ago
• 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
• 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

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Geologic Time Scale
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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
• 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

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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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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

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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

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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 and gabbro

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Plate Tectonic Theory

• Lithosphere is broken into individual pieces or
  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

• Plate boundaries are marked by
• Volcanic activity
• Earthquake activity
• At plate boundaries
• plates diverge,
• plates converge,
• plates slide sideways past each other

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Plate Tectonic Theory

• Types of plate boundaries

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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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Next time Chapter 3 Plate Tectonics