Section 1 - Introduction, History, Geologic Time

Introduction to Geology & Soil Mechanics

Introduction - Lecture Notes

What do the following items have in common?

Silica, (Alkaline Silica)
Aluminum Silicate
Coal Tar
Crystalline Silicate
Americium 241 - Radioactive
Calcium Sulfate
Titanium Dioxide
Lava Rock (Landscaping Rocks, etc.)
Industrial Quartz


These are ingredients found in products at Fleet/Farm in Menomonie, WI.  Of course, think of all the products containing steel, aluminum, and brass.  (not a complete ingredient list):

Sheetrock Patching Compound:  plaster of paris, limestone, dolomite, expanded perlite, mica, attapulgite, kaolin
Salt Bricks: Halite
Detergent: sodium silicate
Sandpaper: sand and gravel
Smoke Detector: 1 microcurie of Americium 241 (radioactive)
Flashlight: nickel, cadmium
Glass Cleaner: Silica
Stove Gasket: graphite impregnated fiberglass
Stove Motar: alkaline silicate
Black Top Sealer: refined coal tar, hydrous aluminum silicate, water (and fatty acid)
        Note: Coal tar is a phototoxic substance which, in the presence of sunlight, can cause a skin reaction similar to an aggravated sunburn, frequently causing blisters.  Coal tar and benzo(a) pyrene containing polycyclic aromatic hydrocarbons have been determined to be human carcinogens.

Vinyl siding wash: sodium hypochlorite, sodium metasilicate
Roof Coating: aluminum flake, amorphous siliceous mineral, calcium carbonate, magnesium carbonate, silicic acid
Crack Filler: quartz, calcium sulfate, biocides
Plaster Additive: crystalline silicate
Construction Adhesive: crystalline silicate, calcium carbonate
Premium F&F House and Trim Satin: titanium dioxide
Primer Latex: talc, mica, zinc oxide pigment, silicon dioxide
Weatherbond Barn and Fence: clay, CaCO3, TiO2, crystalline silica
Copper Wires, Quartz Halogen Lights
Tile Cutting Wheel: Diamond impregnated wheel
Landscaping stones: lava rocks, etc.
Sand Blasting: industrial quartz, sand (silica)
Livestock additive: cobalt carbonate, magnesium oxide, (many oxides), phosphorus and salt
Cargill Trace Mineral Salt: Zn, Mg, Fe, Cu, I, Co

The "big picture"

Geology is generally divided into physical geology and historical geology.

Physical geology is the study of physical processes that occur on earth and the material composition of the earth.  In recent times, these physical principles have been used to study other terrestrial planets within our solar system.

Historical geology examines the time evolution of material structures and life on earth.  This examination focuses on layered rock records and fossils.

Just about everything we encounter (including ourselves) are derived from the earth.  The tough question is "What is not related to geology?"

The other part of this course focuses on soil (only for PHYS-257).  Soil Mechanics is a study of the engineering properties.  How does soil respond to external forces?

It is instructive to make a short excursion into discussing the scientific method of investigation.
In short:

Scientific Method

In long:

  1. Define a problem or make an observation.
  2. Hypothesize a theory to describe or explain observation.
  3. Test the theory.  Can it predict anything?  Is it reproducible?
  4. Can others reproduce the results and make the same conclusions?
  5. Modify or discard theory if steps 3 and 4 are unsuccessful.  Go back to step 1.
  6. If it is consistently reproducible and almost all of the scientific community agrees with the theory, it becomes a natural law.  One should view natural laws and theories as "works in progress" to which some laws and theories are stronger than others.  Stronger in the sense of reproducibility and predictive power.

Two forms of logical reason form the basis of most scientific thought.  For deductive reasoning, if the premises are true, then the conclusion has to be true.  Such that,

If all ford trucks built in '76 have seat belts and Ted's ford truck was built in '76, then Ted's truck has a seat belt (or, at least, originally had a seatbelt if it wasn't removed).

For inductive reasoning, no matter how much evidence exists for a conclusion, the conclusion could still conceivably be false. 

Suppose someone eats 5 apples out of a barrel of 100 and finds each of the 5 apples to be tasty.  From this, they conclude that all the apples are tasty.

One can have weak or strong inferences based upon inductive reasoning.  Many "scientific" studies are plagued with the problem of distinguishing between a causation verses a correlation.  This seems to be most true in the field of sociological studies.  The field of geology has many principles based upon inductive reasoning.

For more reading, here is a study guide to scientific findings published in the New York Times.
An Introduction to Science - Dr. Steven D. Schafersman, Miami University
Introduction, Earth Formation, and Natural Sciences - Lecture Notes, Dr. Susan DeBari, SJSU
Google - Search for Physical Geology Lecture Notes


Historical Development - Lecture Notes

When did geology begin to establish a scientific foundation?

If we go back 2 or 3 centuries, we would find that most people (including scholars) had a very poor understanding of the age of the earth.  Compounding this problem was a tendency to attribute unusual observations to divine intervention or catastrophism.  Such that, sedimentation rock layers 10,000 feet into the air were observed to contain fossils of organisms that lived underwater.  This was difficult to rectify with current earth processes if one assumes the earth to be relatively young (~10,000 years).

Archbishop James Ussher (1581-1656) studied history and biblical text to determine that the earth was created on Sunday, October 23, 4004 BC.  Adam and Eve were driven from Paradise on Monday, November 10, 4004 BC and the Ark touched down on Mt. Ararat on Wednesday, May 5, 1491 BC.  A scientific analysis of geology indicates this to be complete folly.

A Scottish medical man, gentlemen farmer, and geologist named James Hutton is credited with putting modern geology onto a scientific footing.  In the late 1700's he published a paper entitled Theory of the Earth With Proofs and Illustrations".

  • He wrote "We find no sign of a beginning - no prospect for an end."
  • He put forth the principle of Uniformitarianism which states that the physical processes operating in the present to modify the earth's surface also operated in the geologic past.  In other words, "The present is key to the past."

Historical Development - Related Web Links

An Introduction to Geology For Ordinary Folks by Terry Wright
A short biography of James Hutton
Google - Search for Historical Geology Lecture Notes


Geologic Time - Lecture Notes

"Nobody hurries geology"  - Mark Twain

"[People] cling to the edge of eternity our passion to know propels us to the stars but we are humbled by the secrets of the earth.  Is this great canyon the work of God or a symphony of nature?  Is it the summation of all grandeur or the grave of the world?" 

- Grand Canyon: The Hidden Secrets, (Destination Cinema), 2002, DVD IMAX movie

The Earth solidified and became a planet about 4.6 billion years ago.  Geologist have subdivided this 4.6 billion years into Eons, Eras, and Periods.  These divisions are based upon major trends in the evolution of life on earth according to fossil records.  In particular, the boundaries between the geologic eras represent times where mass extinctions have occurred.

Geologic Time

 Geologic Time



Pennsylvania (Carboniferous)
Mississippian (Carboniferous)


Phanerozoic means visible life (Greek origin).
Cenozoic means recent life.  Also called the "Age of the Mammals".
Mesozoic means middle life.  Also called the "Age of the Reptiles" or "Age of the Dinosaurs".
Paleozoic means ancient life.  Also called the "Age of the Fish".
(Be careful, just because the Paleozoic era is called the age of the fish doesn't mean there were no fish in the Mesozoic era.  And early humans did not exist during the reign of the dinosaurs.  Hollywood sometimes depicts humans with dinosaurs as in the "Land Before Time".)

Mammoth Site
Paleontologists working at the Mammoth Site dig site in Hot Springs, South Dakota.  A mammoth tusk is being uncovered in the foreground.  The fossils at this site date back to about 26,000 years.

Tyrannosaurus Skull
Tyrannosaurus Skull
66 Million Years Ago, Cretaceous
(The size of this skull grew to about 1.46 m or about 5 feet long.) 

The era are bounded by profound changes in world-wide life forms.  Plus, the furthur back one goes the more limited our knowledge becomes.  It is important to note that when the "early paleozoic" time is discussed, the term "early" means "older".  The term "late paleozoic" time implies "young" or an age of about 260 million years old.

The Cambrian period represents the first clear and recognizable fossil records of life.  However, scientist have evidence supporting the existence of simple life forms (such as bacteria) going back over 3 billion years ago.  A detailed description of this boundary between the cambrian period and pre-cambrian time can be found here.

A good mnemonic device for remembering the sequence of periods is
"Quit Telling Crazy Jack That Perry Como Died Slowly Over Coals."

"...The earth scorns our simplifications, and becomes much more interesting in its derision.  The history of life is not a continuum of development, but a record punctuated by brief, sometimes geologically instantaneous, episodes of mass extinction and subsequent diversification.  The geologic time scale maps this history, for fossils provide our chief criterion in fixing the temporal order of rocks...Hence, the time scale is not the devil's ploy for torturing students, but the chronicle of key moments in life's history...I make no apologies for the central importance of such knowledge."  [source: Gould, S.J., 1989, Wonderful Life, W.W. Norton and Co.]

Local History

The surface of the earth observed today represents a complex series of geological events that began ~4.6 billion years ago.  Wisconsin has two major physical provinces (areas with similar geology): Canadian Shield and Stable Continental Interior.  Northern Wisconsin (or Southern Canadian Shield) area is call the Superior Upland Province and is mostly metamorphic and igneous rocks of Pre-cambrian age.  It has been subjected to folding, faulting, and igneous activity.  Southern Wisconsin (or Northern Stable Interior) is called the Central Lowlands Province.  It is flat or gently folded sedimentary strata of paleozoic or younger age.

Dating Techniques (Radioactive and Non-radioactive)

Non-radioactive: Tree Rings (Bristlecone Pine > 4,000 years old), Rock Strata, Astronomy (Hubble's Law, Star Clusters), Electron Spin Resonance, Thermoluminescence (radiation changes to rock crystals), Mitochondrial DNA (mutation rate), Amino Acid analysis (gradual change)

[Tree Ring research - or Dendrochronology - has enabled a continuous record of earth's climatic history dating back 8,000 years.]

Sitka Spruce
Sitka Spruce Tree in Olympic National Park (WA) that is about 500 years old.

Tree rings
Cross section of a tree that was about 500 years old when fell.  This section of it shows the rings for about 250 years.  (This tree grew in Olympic National Park.)

The configuration of rock strata can give an indication of relative age.  The principle of superposition can be stated as follows: In a sequence of strata (i.e. sedimentary rocks or lava flows) that have not been overturned by crustal deformation, the older layers are on the bottom and the youngest are on the top. If an igneous rock unit in the form of a dike, stock, or batholith cuts across another rock, the igneous rock unit is said to have a cross-cutting relationship to the other rock and is younger. The study of fossils also provides a means of determining the relative ages of the strata in which fossils occur.

Some Terminology in Dating Rock Strata:
    Unconformity represents a period where deposition occurred, then ceased and erosion began, then erosion stopped and deposition resumed.  Uplift may also play a role.  Here are some specific types of unconformities:  

Angular Unconformity is an unconformity with the deeper sedimentary rock layers tilted with respect to the overlain, flatter lying strata.
Disconformity is an unconformity with the deeper sedimentary rock layers parallel with the overlain rock layers.  This unconformity is difficult to identify.
Nonconformity represents a break between older metamorphic or igneous rocks with younger sedimentary rocks overlaying them.

Example of Relative Dating


By applying the relative dating principles, the rock strata in this profile can be relative dated and unconformities can be identified.  Try to relative age date these strata and identify at least one unconformity.  After attempting this exercise on your own, click here for the solution.  

Radioactive (or Radiometric Dating)

Some naturally occuring nuclei within atoms are unstable.  Such that, the nuclei are in a quantum mechanical energy state that will spontaneously decay (by photon or particle emission) over time into a more stable energy state.  How quickly a radioactive nuclei decays depends on its half-life.  Half of the original nuclei will remain un-decayed after one half-life of time has transpired.

where T is the half-life of the parent nuclei, No is the original number of parent nuclei, N is the number of un-decayed nuclei.  This can also be expressed as



    An absolute age of some rocks or fossils can be determined based on the radioactive decay of certain elements. To determine the age of a given mineral or rock, the amount of "parent" to "daughter" atoms need to be carefully measured along with the decay rate of the parent (and the daughter if it is also radioactive). Igneous rocks and minerals, when dated, give the age of crystallization (or solidification). Metamorphic rocks can sometimes cause inaccurate radioactive dating due to the removal of daughter atoms. The longer the half-life of the parent, the older the rock is that can be dated.

[Note:  The atomic elements are usually denoted as  with A being the atomic mass or atomic weight (equal to the number of protons plus neutrons in the nucleus), Z is the atomic number (equal to the number of protons in the nucleus).  The Z must be consistent with the abbreviation of the element, El.  For example, is carbon 14 (an isotope of carbon 12).  Isotopes have the same Z (or element name) but a different A. ]

Carbon 14 Dating

    Perhaps the best known radioactive dating is based on . This is used to date organic remains. The ratio of to remains constant in an organism as it lives. Upon dying, the begins to decay into but the amount of remains constant. Therefore, an accurate measurement of the ratio of their amounts gives an age. Since has a relatively short half-life of 5,730 years, this method is accurate for ages less than about 60,000 years.  The ratio of in living organisms is 1.2x10-12 (source: Physics Education, March 2004, p. 137).

Radon Fact Sheet For Construction

All about radiation and risk analysis.  (No hypochondriacs allowed into this link!  Everything you wanted to know about radiation and quantifying risk but were afraid to ask.)


Geologic Time - Related Web Links

Radiometric Dating of Rocks (USGS)
On-line "Geological Time Machine"
USGS On-line book Geologic Time by William L. Newman
USGS On-line book FOSSILS, ROCKS, AND TIME By Lucy E. Edwards and John Pojeta, Jr.
Natural History Museums
Grand Canyon Explorer
Radiometric Dating of Rocks and Isotopes, History of Radiation  
Other Geologic Time Charts - University of Calgary, Geology and Geologic Time from UC-Berkeley, YOGI's Geologic Time Chart
Stephen Gould on evolution
An on-line book with a detailed analysis of the teaching of Creationism verses Evolution debate (National Academy Press)   
Geology of Mt. Diablo - I (instructor of this course) used to live nearby this Mountain
Tunguska impact in Siberia (1908) - One of the strangest natural events recorded in recent times.
Google - Search for Radioactivity Animations
Google - Search for Geologic Time

Human Origins - A site devoted to exploring human origins

"The Smithsonian Barbie" (humor)

On-line Lecture Notes

GOOGLE search for lecture notes on geologic time
Dr. Pamela Gore's On-line course in Historical Geology (geologic time, evolution, etc.) and Radiometric Dating
Dr. Susan DeBari, lecture notes on Earth Structure and Geologic Time
Dr. Susan DeBari, lecture notes on Geologic Time and Relative Dating
Dr. Tom Clifton, lecture notes on History of Life
Google - Search for Geologic Time Lecture Notes

Review Quizzes
Section 1

Review Quiz Section 1
Tarbuck and Lutgens, Essentials of Geology, Self-Quiz (Select Chapters Introduction To Geology or Geologic Time or Earth History: A Brief Summary)

Grand Canyon

Grand Canyon, 1991
To see a schematic of the age of each rock strata in this picture go to the PBS web site Lost in The Grand Canyon, The American Experience.

Grand Canyon