Outline for Dr. Heaton's ESCI 103 class
Principles of Earth Science II
or Historical Geology
Textbook: Harold L. Levin, The Earth Through Time,
8th Edition
Chapter 2 – Early Geologists Tackle History’s Mysteries
Key Historical
Figures and their Contributions
Herodotus (450 B.C.) and later Leonardo da Vinci (1452‑1519)
Recognized fossils
as remnants of ancient life that lived where the fossils are found
Nicolaus Steno
(1638‑1687)
Principal of Superposition (higher
layers of rock are younger than lower layers)
Principal of Original Horizontality
(tilted layers of rock were formed horizontal)
Principal of Original Lateral
Continuity (rock layers are continuous over large areas)
Abraham Werner
(1749‑1817)
Neptunist (believed all rocks, including
basalt, precipitated out of the ocean)
James Hutton (1726‑1797)
Plutonist (believed that igneous rocks
formed from a liquid melt)
Proposed long geologic cycles (like a
heat engine) to explain origin of soil for farming
Father of Uniformitarianism (old earth,
gradual change, "present is the Key to the past")
Principal of Unconformities
(sedimentary discontinuities representing time hiatuses)
William
"Strata" Smith (1769‑1839)
Principal of Fossil Succession (using
fossils to correlate rock ages)
Mapped the rocks of
Georges Cuvier
(1769‑1832)
Famous anatomist, defender of
Catastrophism and mass extinction
Mapped the rocks of
Charles Lyell (1797‑1875)
Principal expounder of
Uniformitarianism, Gradualism, and a cyclic history of life
Principal of Cross‑cutting
Relations (dating of features by their effects on each other)
Principal of Inclusions (pieces of
older rock are encased within younger rock)
Charles Darwin
(1809‑1882)
Follower of Lyell, defender of
Uniformitarianism and Gradualism
Proposed Evolution by Natural Selection
to explain faunal succession
Proposed another evolutionary theory to
explain coral reefs
Lord Kelvin (1824‑1907)
Physicist who claimed that Lyell's
earth was an absurd perpetual motion machine
Claimed that the sun and the earth were
rapidly cooling from an original molten state
Calculated that the earth was too young
for
His ideas were negated with the
discovery (around 1900) of nuclear reactions
Key Historical
Issues
The age of the
earth and its features
Rapid catastrophic
change vs. slow gradual change
Time's arrow vs.
time's cycle
The ultimate cause
of things (natural or supernatural)
Historical science
requires different approaches than laboratory science
Detailed study of
modern processes, comparison with past features (Actualism)
Recognition of past
processes no longer operating today
Hypothesis testing,
multiple working hypotheses
Chapter 3 – Time and Geology
The Geologic
Time Scale: "type sections" named locally and later correlated
worldwide
Hierarchy of Eons, Eras, Periods,
Epochs, developed in early 1800's
Dates in years added in 1950's using
radiometric dating
Learn Eons, Eras,
Periods, Epochs of Cenozoic, and dates of era boundaries
Stratigraphy is the
science of correlating sedimentary rocks.
Geochronology is
the science of dating geologic events.
Adam Sedgwick‑‑named
Cambrian, used lithology as basis (bad for correlation)
Roderick Murchison‑‑named
Silurian, used fossils as basis (better method)
Charles Lyell‑‑named
epochs of Cenozoic based on percentage of modern species
Cambrian,
Ordovician, Silurian, Devonian: named for places and tribes in
Carboniferous:
named for the important coal deposits it bears in
Subdivided into Mississippian and
Pennsylvanian in
Permian: named for
the
Triassic: named for
the three-fold division of rocks of this age in
Jurassic: named for
the
Cretaceous: named
for the chalk deposits it contains throughout
Tertiary and
Quaternary: remnant names from the original "Primary, Secondary"
nomenclature
Paleogene and
Neogene: modern official periods of the Cenozoic Era
Classification & Hierarchy of
Sedimentary Units
Time Units Time‑Stratigraphic Units Rock Units
Eon = Eonothem
Era = Erathem
Period = System » Group
Epoch = Series » Formation
Age = Stage » Member
Chron = Zone
(chronozone)
Lithostratigraphy—using rock type as
the basis of correlation
Formations are based on
lithology (rock type) and can be "time transgressive"
They also cover a
limited geographic area and cannot be correlated worldwide
The trick is
relating stratigraphy (rock layers) with time (actual age)
Biostratigraphy—using fossils as
the basis of correlation
Fossil zones are the
stratigraphic ranges covered by index fossils (short-lived species)
Strategies for
aging events
Relative dating‑‑establishing
a sequence of events irrespective of time or duration
Examples: superposition, cross‑cutting
relations, fossil correlation, etc.
Absolute dating‑‑giving
a date (i.e. in years) to each past event
Requirements of a
natural clock
1) Irreversible,
non-cycling process
2) Constant or
uniformly changing rate
3) Measurable
initial condition
4) Measurable final
condition
Early (failed)
attempts at dating the earth
Rates of deposition
& rates of erosion (non‑uniform rate, but did show that the earth was
old)
Saltiness of the
ocean (involves a cycling process rather than cumulative process)
Heat flow from the
earth [Lord Kelvin] (failed to account for heat from radioactivity)
Radiometric dating
(works best with igneous rocks)
Atoms, nuclei,
protons, neutrons, atomic number, mass number, and isotopes (nuclides)
Radioactive decay,
parent isotope, daughter isotope
Types of decay:
Alpha, Beta, Gamma, Electron capture
Statistical
probability and the law of large numbers
The Half‑life
concept: the time required for half the unstable atoms to decay
Each radioisotope has its own half‑life
value which must be experimentally determined.
Isotopes useful in geology have very
long half‑lives because they are dating old events.
Isotopes most
useful in dating past events on earth
Uranium‑238 >>
Lead‑206 4.5 billion year half‑life Multiple α and ß decays
Uranium‑235 >>
Lead‑207 0.7 billion year half‑life Multiple α and ß decays
Potassium‑40 >>
Argon‑40 1.3 billion year Half‑life Electron capture
Rubidium‑87 >>
Strontium‑87 49 billion year half‑life ß decay
Carbon‑14 >>
Nitrogen‑14 5730 year half‑life ß decay
A closed system is
needed to maintain the components and predict the initial condition.
Blocking
temperature is the temperature below which a mineral becomes a closed system.
Isochrons are plots
from multiple samples that indicate potential problems with the dates.
Concordant dates:
similar results from multiple radioisotopes (always good)
Discordant dates:
inconsistent results from multiple radioisotopes (sometimes bad)
Know the assumed
initial conditions and what event is being dated with each method.
Know what
assumptions each dating method is based upon and any potential for error.
Know what type(s)
of decay is (are) involved with each method and the half‑life.
Other dating
techniques
Fission track
dating‑‑counting holes in minerals made by energetic decay products
Magnetostratigraphy‑‑the
record of reversals of the earth's magnetic field
Time‑parallel
surfaces: ash beds, tillites, magnetic reversals, fossil origins & extinctions
Relative and
absolute dating can be used in conjunction with one another to bracket true
ages.
Radiocarbon Dating
Carbon-14 is
generated in the atmosphere and cycles through the food chain with
Carbon-12/13.
When an organism
dies its Carbon-14 decays back to nitrogen and escapes into the atmosphere.
Comparing Carbon-14
to Carbon-12 & 13 in a sample tells you when the organism died.
Chapter 4 – Rocks and Minerals:
Documents that Record Earth’s History
Minerals (naturally
occurring solids, orderly atomic arrangement and chemical comp.)
Silicates
Framework silicates: quartz, feldspars
(orthoclase, plagioclase)
Sheet silicates: biotite, muscovite,
chlorite, clay minerals (kaolinite, talc)
Double chain silicates: amphiboles
(hornblende)
Single chain silicates: pyroxenes
(augite)
Orthosilicates (isolated tetrahedra):
olivine, garnet
Carbonates:
calcite, dolomite
Phosphates:
apatite, turquoise
Sulfates: gypsum,
barite
Sulfides: pyrite,
chalcopyrite, sphalerite, galena
Chlorites: halite,
fluorite
Oxides: hematite,
limonite, magnetite, corundum, ice
Native elements:
copper, gold, sulfur, graphite, diamond
Igneous Rocks (form from a
liquid melt, rocks in bold are most common)
Composition
Felsic: Granite/Rhyolite
Intermediate:
Diorite/Andesite
Mafic: Gabbro/Basalt
Ultramafic:
Peridotite/Komatiite
Texture
Plutonic (coarse‑grained,
intrusive): Granite, Diorite, Gabbro, Peridotite
Volcanic (fine‑grained,
extrusive): Rhyolite, Andesite, Basalt, Komatiite
Volcanic glass:
Obsidian, Pumice
Sedimentary Rocks (formed at earth's
surface from sedimentary particles, layered)
Clastic sediments‑‑made
from fragments of pre‑existing rocks (via erosion)
Conglomerate/Breccia,
Sandstone, Siltstone, Shale, Coal
Chemical sediments‑‑sediments
precipitated out of water (organic or inorganic)
Limestone (Chalk, Coquina, Oolitic
ls.), Dolostone, Chert, Rock salt, Rock gypsum
Lithification‑‑occurs
by the compaction and/or cementation of sediments
Sorting‑‑the
process by which similar clastic particles are collected together
Sedimentary
structures‑‑cross bedding, mud cracks, varves
Metamorphic Rocks (recrystallized in
the solid state)
Factors:
temperature, pressure, intergrannular fluids
Low vs. high grade
metamorphism‑‑indicated by index minerals, partial melting
Foliation‑‑planar
texture in rock running perpendicular to stress
Settings: burial
metamorphism, regional metamorphism, contact metamorphism
Sandstone >>> Quartzite (non‑foliated)
Limestone >>> Marble (non‑foliated)
Shale >>>
Slate >>> Phyllite
>>> Schist >>>
Gneiss (foliated)
Granite >>>
Gneiss (foliated)
Basalt >>>
Greenstone (non‑foliated)
Chapter 5 – The Sedimentary Archives
Tectonic Settings
Mountain Belts‑‑areas
of recent uplift from either collision or inflation by magma
Cratons‑‑non‑mountainous
portion of continents, eroded flat, very old
1) Shields: exposed
basement metamorphic complexes, often gneiss intruded by granite
2) Platforms: areas
with flat‑lying sedimentary rocks covering the basement complex
Environments of
Deposition
Marine Deposition (fine sediments,
clastic or biogenous/hydrogenous, great lateral uniformity)
Continental
Shelves: shallow water, abundant life, much sediment (much shale &
limestone)
Continental Slope:
unstable accumulation, erosional canyons formed by turbidity currents
Continental Rise:
turbidites form deep-sea fans at base of submarine canyons
Abyssal Plains:
slow sediment accumulation covers abyssal hills (very fine clays & oozes)
Transitional
Deposition (shoreline, high rates of deposition, clastic sediments from rivers)
Deltas: very thick
accumulations of lag gravels, channel sands, backswamp clays and coal
Beaches: longshore
drift, clean quartz & magnetite sand accumulation
Barrier
Island/Lagoon Sequences: sandstone and coal form in adjacent environments
Tidal Flats: muds
carried by tidal waters in areas of constantly‑changing shoreline
(Narrow linear
environments along coast, resultant rock units are often time‑transgressive)
(Thick
accumulations of sediments can form in shallow water because of subsidence)
Continental
Deposition (includes coarsest sediments, mixed local environments)
Meandering Rivers:
floodplains, point bars, lag gravels, backswamps, oxbow lakes
Braided Rivers:
thick & wide deposits of channel sands
Alluvial Fans/Playa
Lakes: coarse conglomerates interfingering with alkali muds
Sand Dunes:
crossbeded sands, indicates strong winds and lack of vegetation
Glaciers: tillite
(with striated cobbles), loess, associated lake & braided stream deposits
Catastrophic
Flooding: rare and distinct, scouring of bedrock, well sorted conglomerates
Features of
Sedimentary Rocks
Coloration
Black Coloration:
unoxidized organic carbon, FeS2, H2S (poor circulation,
organic deposition)
Red Coloration:
ferric (oxidized) iron (with evaporites indicate warm & arid conditions)
Can result from red source rock,
subaerial oxidation, or subsurface alteration
Texture
Particle size
(Wentworth scale), sorting, roundness/sphericity, grain orientation, matrix/cement
Sedimentary
Structures (features larger than grains)
Mud cracks:
intermittent wet and dry conditions
Cross-bedding:
planar (beach and dune deposits), trough (braided rivers sediments)
Ripple Marks:
symmetric (oscillating waves), asymmetric (stream or wind currents)
Graded Bedding:
fining upward (turbidity currents: coarse fraction settles first, fine fraction
last)
Geopetal
structures: indicate "up" direction during deposition (ripples, mud
cracks, foot prints)
Chapter 5 – The
Sedimentary Archives, cont.
Sandstones (indicate source
rock & distance of transportation [maturity])
Quartz Sandstone:
rounded quartz grains, other minerals weathered away (long transportation)
Arkose: >25%
feldspar (close proximity to granite or gneiss source rock)
Graywacke: poor
sorting, fine matrix (fast erosion or high volcanic input, active tectonic
areas)
Lithic Sandstone:
many rock fragments (deltaic coastal plains, short transportation)
Limestones (carbonates, form
in precipitation settings far from clastic sediment sources)
Can be composed of
shell fragments, tiny algae fragments, inorganic oöids, etc.
Carbonate Platforms
are broad shallow continental shelves dominated by carbonate deposition
During periods of
high sea level (Cambrian, Mississippian) carbonate deposition was extensive
Dolomite forms when
evaporating sea water develops high concentrations of magnesium
Shales (made of very fine
particles derived from erosion, mostly of clay minerals)
Clay minerals form
from the weathering of other minerals
These particles are
so small that they can be carried great distances suspended in water
Typical
Depositional Settings
Sandstone‑-in
deltas and beaches (nearest shore)
Shale‑‑near
shore where carried by local currents
Limestone‑‑farthest
from shore where clay particles are not present to dilute precipitates
Changes in Sea
Level
Transgression‑‑a
rise in sea level causing flooding ("transgression") of the land
Regression‑‑a
fall in sea level causing the exposure of previously drowned land
Transgression
sequences: unconformity (bottom), sandstone, shale, limestone (top)
Regression
sequences: limestone (bottom), shale, sandstone, unconformity (top)
Unconformities
Disconformity‑‑sedimentary
layers are parallel above and below the unconformity
Angular
unconformity‑‑sedimentary layers below meet the unconformity at an
angle
Nonconformity‑‑igneous
or metamorphic rocks underlie the unconformity
Chapter 6 – Life on Earth: What do Fossils Reveal?
Previous
assumption: special creation of fixed species, spontaneous regeneration, no
extinctions
Georges de Buffon
(1707 1788)
Defined the species concept, observed
that environments change species over time
Noted that characters are inherited in
all species, proposed a vague notion of evolution
Carolus Linnaeus
(1707‑1778)
Classified life hierarchically:
kingdom, phylum, class, order, family, genus, species
Jean Baptiste de
Lamarck (1744‑1829)
Believed in an automatic regeneration
of life (extinctions impossible)
Believed that life forms evolve with
the most complex species being the oldest
Proposed a mechanism for evolution: the
inheritance of acquired characters
Georges Cuvier
(1769‑1832)
Opposed the evolutionary ideas of
Buffon and Lamarck, believed in the fixity of species
Demonstrated the reality of extinction,
short‑lived "index fossils" useful time indicators
Louis Pasteur (1822‑1895)
Demonstrated that life can only arise
from existing life (no spontaneous generation)
Charles Darwin
(1809‑1882)
An excellent biological observer from
his youth, dabbled in medicine & the clergy
Converted to the notion of a very old
& uniformitarian earth by writings of Charles Lyell
Voyage of the Beagle (1831‑1836)
exposed him to fossils and to island biogeography
Set a whole new standard for the
collection of scientific specimens, meticulous researcher
Convinced of evolution (descent with
modification) of species by "natural selection"
Natural Selection
(adapted from socioeconomic theories by Adam Smith & Thomas Malthus)
Organisms produce far more offspring
than the environment can sustain
Offspring exhibit variation, and these
variations are heritable
Environmental factors
"select" which variants survive to produce the next generation
By sustained selective pressure a
species can be radically modified over time
A gradually changing earth (Lyell)
produces gradually changing species (
Evidences of
evolution (i.e. facts that evolution explains well)
Historic small‑scale changes
within species in nature (natural selection)
Historic large‑scale changes in
domesticated plants and animals (human selection)
Common body plans and biochemistry in
diverse organisms (homologies)
Common embryologic developmental stages
in all vertebrates
Rudimentary or "vestigial"
organs
Blatant imperfections (maladaptations)
and oddities with historical explanations
Biogeographic distributions (habitat
barriers, colonization factors, isolated populations)
The fossil record (the only true
documentation of evolution)
a) Linking fossils on the large scale (intermediate forms)
b) The dilemma of the fossil record at the species level
"Phyletic Gradualism" vs.
"Punctuated Equilibrium"
Genetics of Gregor
Mendel (1822‑1884)
Provided the long‑sought basis
for inheritance
At first seemed contradictory to
evolution because it limited possible variation
Eventually formed a foundation for
evolution via mutations and genetic recombination
Disorder of the genetic code (like a
jumbled computer program) suggestive of evolution
Inheritance of
Acquired Characters has some truth to it
Human culture is passed on in a
Lamarckian fashion
Immunities (via acquired antibodies,
not genes) are often inherited
Viral DNA and "jumping genes"
may sometimes be passed on to offspring
Know the definition
and examples of these terms
Divergent evolution‑‑a
single species giving rise to morphologically distinct species
Convergent
evolution‑‑distant species coming to look superficially alike
Iterative evolution‑‑one
lineage repeatedly giving rise to similar descendants
Adaptive radiation‑‑one
form quickly giving rise to many diverse descendants
Evolutionary trend‑‑a
long‑term evolutionary change in the same direction in a lineage
Sympatric
speciation‑‑a single population diverging into two different
species
Allopatric
speciation‑‑isolated populations of a species diverging to form
different species
Preadaptation‑‑a
body structure switching from one function to another
Neoteny‑‑a
juvenile trait being retained into adulthood
Microevolution‑‑small‑scale
changes in a lineage
Macroevolution‑‑development
of an entirely new body form or structure
Extinction‑‑the
termination of a lineage
Uses of Fossils
1) Learning about
ancient life to better understand our world (Paleobiology)
2) Geologic time
correlation (Biostratigraphy)
Index fossils (fossils with a short geologic
time range)
Biozones: range zones, assemblage
zones, concurrent range zones
The problem of reworked fossils
3) Environmental
indicators (Paleoecology)
Subdivisions of the marine and
terrestrial realms, habitats
Ecosystems, trophic levels, niches
4) Reconstructing
ancient geography (Paleobiogeography)
Dispersal (corridors, filter routes,
sweepstakes routes)
Body fossils‑‑bodily
remains of prehistoric organisms
Trace fossils‑‑tracks,
trails, burrows, etc. (Ichnology)
Types of
preservation‑‑permineralization, carbonization, etc.
Advantages for
preservation‑‑hard parts, rapid burial, etc.
The fossil record
(an accidental historical record) is a good but incomplete record of life
The Evolution/Creation Debate
Ideas Popular in Western Religions
God created the universe (primarily for Man) and is the
ultimate authority on all matters.
Prophets reveal God's will and purpose; past scripture
is a substituted for prophets today.
Argument from Design: the best proof of God's existence
is his creations (William Paley, 1802)
Deism: the world is a self‑running machine set in
motion by God (René Descartes, 1596‑1650)
Biblical Creationism: the world was created in 6 literal
days, a world-wide flood killed most life
The Fundamentals of Science
Observation and Experiment—collecting data from the
physical world itself to learn its history
Rational Thinking—careful evaluation, hypothesis
testing, theory generation (no higher authority)
Naturalism—the belief that all things have come about by
way of consistent natural laws
The Dethroning of God as Creator (finding explanations
for origins that don't invoke God)
1) Nebular Hypothesis of Laplace & Kant for the
origin of the solar system and the earth
2) Uniformitarian Geology of Hutton & Lyell for the
origin of the earth's rocks and features
3) Evolution by Natural Selection of Darwin &
Wallace for life on earth
The Genesis Account
1) God created heaven and earth and the various
"kinds" of life (Genesis 1:1‑2:7, Exodus 20:11)
2) The Fall of Adam brought death into the world
(Genesis 2:16‑17, 3:1‑24, I Cor. 15:21‑23)
3) The Flood of Noah killed off nearly all life on earth
(Genesis 6:5‑8:19)
Ways of Harmonizing Geological Observations with Genesis
1) Day-Age Theory: each "day" of Creation is
really a long geologic time period
2) Gap Theory: there was a long time gap between the
first two verses of Genesis
3) Creation Science: earth is ~6,000 years old, Noah's
Flood created the sedimentary rocks
Spectrum of Positions on Science and Religion
1) Atheistic Evolution: evolution is the only
explanation needed for life on earth
2) Theistic Evolution: evolution is true, but God guided
the process (Catholic viewpoint)
3) Day-Age & Gap Theories: evolution is false but
there were long geological ages
4) Creation Science: the earth is young, Noah's Flood
deposited most sedimentary rocks
The History and Nature of Creation Science
Originated with a Seventh Day Adventist named George
McCready Price (1870‑1963)
Price
differed from other creationists by attacking geology rather than biology.
Made popular to Protestants by Whitcomb & Morris' The
Genesis Flood (1963) & Jerry Falwell
Morris' Scientific Creationism presents
Creationism as a Science rather than a religion.
Science is
the modern way of knowing all truth, so even religion must be scientific.
Creationists
have tried (unsuccessfully) to get Creationism into the science classroom.
Creationism in Court
1) Tennessee Anti-Evolution Act (1925) prohibited the
teaching of evolution in public schools
Scopes
Monkey Trial at
2) Equal Time laws (equal time required for evolution
and Biblical view of origins)
These were
ruled unconstitutional at the outset because of Separation of Church and State.
3) Arkansas Balanced Treatment Act (1981) based on the
Evolution/Creation science distinction
Judge
Overton banned implementation of the law because of its obvious religious
basis.