Revised 8 / 06 (Monroe 6th ed.)

Orientation and Introduction: Geology 101




Introduction to the earth

Introduction to Geologic Time

The age of the earth

Geologic Time and the Relative Time Scale

Fossils and the geologic record

Timeline Lab



Who am I?

Damn good question!

Why are you here?

Scope of the course

Really a study of Earth Science

We will be covering many things other than what is strictly 'geology' in the classical sense

Astronomy, oceanography, etc.

Try to keep it fun - not boring

This requires lots of give & take

Active class participation

The Syllabus

A general guideline

We will almost certainly deviate

Internet: Use it - it will probably help

Give me as much feedback as you want - I'm always trying to improve my efforts

Geology and Earth Sciences are extremely interconnected

We will be moving around a lot

Briefly touching on a future topic to help understand where we are at the time

Some topics naturally go together

Example: Plate Tectonics and Ocean Floor

The Text

The book is important

Much, but not all of what we talk about is covered in the book

Not my personal favorite, but relatively inexpensive

Will supplement with additional info

Not take in order - will jump around quite a bit

Also... I've drawn on many other sources

When I say "the book..." I many not always be referring to our text

The Labs

Great manual, and it works for G102 also

Really focuses on topographic maps in the sections on landforms

May require a separate manual for G103

More focused on earth history and geologic mapping

When: Not every time, but when appropriate

Check the syllabus


No reason for anyone to fail this class

Graded as follows:

2 Exams (or their equivalent) (25% each)

1 GeoFantasy Presentation (25%)

The APE factor (attendance, participation, & enthusiasm) (25%)

Open-note tests: Here's the deal

Allowed one (1) page of notes on each exam (8.5 X 11; both sides)

From lecture or book

No photocopies!

Re-sketch maps, etc. if you feel the need

Abuse this priveledge and lose it!

Active participation is required!

Only requirement is that it contributes to whatever is going on at the time

This covers a large amount of acreage

Field Trips

At least one each term (may be rained/snowed out during winter term)

Real geology

Apply GeoFantasy to the real world

Not required but strongly recommended!

Any questions so far?


Introduction to the earth

Anyone who has traveled at all realizes that not all parts of the earth are the same

Both surface features and the rocks below the surface

It's also clear that the earth is not ever-present and unchanging

Anyone stuck behind a rockslide knows that

Many examples:

Mt. St. Helens


Spokane Flood

Multnomah Falls rockfall

Glacier Point rockfall

Geology is the study of these surface and bedrock features

What they are

How they were formed

Geologists need to be able to see the actual rocks

Unfortunately, there's a lot of soil and other loose stuff covering the surface

Not to mention placed covered by water

Look for places where the soil cover is gone or never developed


Let's hear it for ridges and stream beds (and road cuts)

In any event, need to get all the dirt and biological contamination out of the way in order to adequately do our job

Not everyone gives geology much respect

Geology isn't a 'Fundamental Science'

Not like Physics, Chemistry, etc.

We can't answer all of our questions by doing empirical experiments

Geology is a 'Multidisciplinary' science

This is a $.50 word which says that it draws strength from many different areas of study

By the time we're done, you will see how it is interrelated to physics, chemistry, biology

Geophysics, geochemistry, etc.

And math? I'll try to minimize the pain.

Geology is also a field oriented science

Much more so than any other of the sciences

The field IS our science!

You can't learn about it sitting in a room (so let's all go home?)

We'll have several field trips over the course of the coming year

The study of geology gives us our only glimpse into the earth's past

This glimpse is admittedly biased, as we will come to learn throughout this course

The view can be extremely selective in most cases

I really like geology and being a geologist

We do easy things

Observe and record

And beat up rocks

It's always tempting to stereotype professions

Example: Docs w/ bad handwriting

Lawyers w/ bad attitudes

Plumbers w/ bad pipes

It is traditional that geologists...

...drink a lot of beer during the wild and crazy phase out a lot

...spend lots of time around a campfire

...have a realistic view of time and space, and are therefore extremely well-adjusted

...are relatively unaffected by much of the normal day-to-day BS which plagues society

And best of all, there are no real "laws" in geology

Not like the fundamental sciences which rely on 'natural laws' to help them make sense (and keep them boring and predictable)

The best we have are a few general guidelines to help clarify some of the mess, such as...

Uniformitarianism - 'the present is the key to the past'

If a process is active today, it's probably worked the same throughout geologic time

Gravity, water running downhill, that kind of thing

As you can see, our 'geological laws' are pretty general!

We'll get to a few more in a couple minutes

It's possible to get a little carried away with all of this legal support!

The concept of uniformitarianism states that there are natural laws that have prevailed on our planet continuously and unchangingly throughout geologic time

'Change' is the rule in geology (as it is in life)

I like to think that a strict uniformitarian view may be too restrictive

You'll find that I preach skepticism in this course

Cast a wary eye and/or ear on all people or things which claim to "know for sure" anything about geology

This includes such modifiers as 'always, never, all, every, forever, etc.'

All in all, though, uniformitarianism is a valid and needed concept

The alternative is that all that surrounds us has no connection with the past, or effect on the future

A world in which there is no continuity, and in which chaos is the overriding principle

DIGRESS TO: Chaos Theory

The concept of uniformitarianism took a while to catch on

DIGRESS TO: Western vs. eastern cultures

In Europe, religious dogma effectively put a lid on creative geologic thought until the 1700's

Basically, the bible teaches creationism and catastrophic natural events to explain the diverse biologic and physical features found on the earth

It's not within the scope of this class to settle the debate between the Bible and Natural Processes, or Bible and Evolution

This IS a class which is in large part based on non-biblical processes and interpretations

If you have trouble with this, I look forward to many spirited discussions over the course of our study

I have no intention of dodging the issue because it is controversial!

In any event...

It does seem possible, however, to safely say that the religious straight jackets of the middle ages were an indication of the fear that the church had concerning anything which could potentially erode its hold on the masses

Fortunately, several free-thinkers attempted to explain natural events in more natural ways

James Hutton (1726-97) and John Playfair (1748-1819) - both were Scottish

Each felt that the geologic features which they observed could have been formed by slow, continuous processes over long periods of time, rather than catastrophic events

Sir Charles Lyell (1797-1875) - Englishman

Expanded on the work of Hutton and Playfair

Started doing detailed studies

"documented the realities of uniformitarianism"

Called the Father of Geology

Charles Darwin (1809-82)

Geologist/Biologist on the HMS Beagle in 1859

Quite a guy!

Wrote "The Origin of Species" based on his observations on that voyage

The method of scientific experimentation is quite different between geology and the 'true' sciences

In the case of the fundamental sciences, the 'scientific method' can be applied

DIGRESS TO: scientific method (wild and crazy idea to stagnation)

In geology, we really can't PROVE anything, because we don't have any 'natural laws' to form a firm foundation for experimentation

Also, many of the processes occur outside of our range of vision

Both spatial and temporal

There is no black and white in geology - only infinite shades of grey

Nothing works in every possible situation (oops, there are those modifiers!)

Laboratory experiments are commonly inadequate in their attempts to duplicate natural processes

The earth is the most complex and well-equipped lab we know of

Trying to duplicate it is similar to playing Motzart on a pair of spoons and a washtub

It may sound fine as far as it goes, but some of the subtleties are missing

In the case of the earth's processes, these subtleties are what define the various shades of grey, and provide for the infinite variation we see all around us

As well as the infinite joy of exploration and discovery

Geology relies on the concept of 'multiple working hypotheses'

Several different theories are proposed to account for an observed result

Additional work concentrates on attempting to DISprove one or another of them until only one remains

More often than not, geological testing is geared towards ruling out possibilities rather than towards proving a theory correct

This additional testing may often result in new theories to be considered

In geology, you can ask one question and get three more as an answer

Sometimes it doesn't seem fair

Geologic hypothesis are much like a weather forecast - both are based of estimates of probability


Introduction to geologic time - the 4th dimension

The study of the earth involves immense quantities of time

In our lives, we can comprehend hours, days, weeks, years (maybe)

The rise and fall of Rome are 'ancient' history, and details of most of what came before that are locked up in legend and speculation

Think of our history of the Greeks, Egyptians, and before into ?

In geology, we are dealing in millions and billions of years

This immense scale is possibly one on the most difficult (although important) concepts to be grasped in geology

Geologists have a healthy respect for time

DIGRESS TO: analog vs. digital clocks

Our view of the earth is not a photograph

More like one frame in a movie

In any event, it is comforting to be a geologist

Lots of us get nervous about human impact on the surface of the earth

A geological view of time is sufficiently broad to allow for healing of any possible scar

Anyway, the passage of large amounts of time is a critical part of geological thought

You will hear me say "Over the course of geologic time..."

A basic tenet (guideline?) of geology is that just about anything can happen if given enough time

Remember the monkeys with typewriters and trying to knock out the Great Books

Our measurements of time on earth reflect our limited scope of time.

We have seconds, minutes, hours, days, and years

Computers have changed our scope to where many talk of portions of a second - examples

No matter what, we don't commonly deal in millions and billions of years

We need to employ "unconventional methods" in order to estimate time intervals throughout geologic history


The age of the earth

Anyone have any idea how old it is?

It has been open for speculation for quite some time, and several "unconventional" time spans have been postulated

Archbishop Ussher (1581-1656)

Added up the 'begats' in the old testament

The earth was formed on the evening of October 22, 4004 B.C.

This date was etched in the cement of church dogma

For a hundred years or so, anyone who questioned this date was liable to be denounced as a heretic (or worse)

Remember, this was when you could be bar-b-qued for questioning the church

Supporters relied on "innumerable catastrophes" to explain the diverse geologic features on earth

The early work of men like Hutton, Playfair and Lyell helped to break out of the straightjacket of religious dogma

New insights into geologic processes allowed 'more scientific' attempts

Early attempts used such things as measurements of stratigraphic sequences

DIGRESS TO: the 3 general types of rock

Lots of problems

How fast are sediments deposited

How fast are they eroded

Is sedimentation continuous

And even if we can figure out all the above

No continuous exposure through all of the earth's history

With all of this in mind (maybe)

William Sollas (1883)

Estimated the earth's age at 26 million years

Far cry from the 6000 years postulated by the church

It's certain that if he had been born 200 years earlier he would have been toast!

Measurements of the amount of salt in seawater - Joly (1899) - Irishman

Lots of problems here, too

Is the rate of salt addition constant

This is directly related to rates of mountain building and tectonics

Which certainly seems to be anything but regular

How about salt removed from the sea due to uplift and evaporation

Some of this salt is re-cycled as the salt beds are eroded

Came up with an age of 100 million years

We currently believe that the earth is 4.6 billion years old

Based on Absolute Age Dating methods

Describe: this is some serious GeoFantasy

Relies on the regular decay of unstable (radioactive) minerals

Allows us to assign absolute dates to many rocks

Many uncertainties (at least to me)

Absolute age dating methods are a fairly recent innovation

Not available in the past

Early workers had to come up with a different way to figure out how old something was


The Relative Geologic Time Scale

Doesn't concern itself with actual ages, only in the RELATIVE order of events

Geologists can use a relative time scale in many situations in geology (Monroe: fig. 1-16, pg. 24)

Many have to do with sedimentary rocks

This leads us to the classical "Laws of Geology" which I promised you earlier

First 2 were developed by Nicolaus Steno (1638-86) - a Danish physician

Law of Superposition

"in any sequence of layered rocks any one layer will be older than the layer above it and younger than the layer below it"

This can be used to determine the relative ages of undisturbed sedimentary sequences

The key term here is "undisturbed sedimentary sequences"

Faulting and folding can play merry hell with superposition

Law of Original Horizontality

States that sedimentary beds are laid down horizontally (or near horizontally)

If they aren't flat, some tectonic force must have disturbed them

DIGRESS TO: Tectonics

There are definitely exceptions to this "law"

Cross-cutting relationships - James Hutton

"if one body of rock cuts across another body of rock, the latter must be older than the former."

Weathering and erosion of pre-existing rock or sediments

Can only happen near the surface of the earth

This "law" is really a negative situation

Based on the absence of any rock record

Results in a gap in the geologic record


Uplift, erosion, and subsidence

These are very common in the stratigraphic record

Can be very difficult to recognize

Especially if there hasn't been any tilting of the sedimentary layers

Grand Canyon - The Great Unconformity

Easy to recognize - angular unconformity and nonconformity

Strickler's Laws of GeoFantasy

Establishing the relative time sequence in a local area is relatively easy

Any given outcrop is usually pretty straight-forward

It's much more difficult on a regional scale

DIGRESS TO : regional vs. local

The best method to be used in correlating separated rock units is to compare the characteristics of the rocks themselves

Physical and compositional

The more distinctive, the better

Marker beds

Time-stratigraphic horizons

The best represent regionally distinctive, widespread, and short duration events

Rock units, fossils, mineral assemblages, whatever

Volcanic ash deposits are excellent examples

These greatly aid in developing a regional time scale

Think of what a marker bed man will be!

Unfortunately, not all sedimentary units are 'regionally distinctive'

Many, if not most, change laterally into subtle to profoundly different types of rocks

Pebble Conglomerate to Sandstone to Shale to Limestone

Near shore high energy zone to quiet, deep water carbonate sedimentation

Facies Changes


Fossils and the geologic record

Fossils are the best and most commonly used correlation tool

This is based on the concepts of natural selection and evolution

Define both

Rapid evolution of short-lived species works best

Fossils are the preserved remains or traces of prehistoric plants or animals

Unfortunately, only Phanerozoic rocks have fossils

And not even all of those have fossils

Basically, we're talking about the last 600 m.y. or so

Also, it is a VERY thin and biased record

Mostly marine organisms

Fossils allow geologists (Paleontologists) to correlate similar rock units across very wide distances

They form the basis for the Relative Time Scale (Monroe: fig. 1-16, pg. 24)

Fossils show clearly that life has changed continuously in form and kind throughout geologic time

Constantly adapting to changing environments due to changes in the earth

Fossils in rocks have proven to be exciting throughout recorded history (and pre-history, too)

Their true meaning, however, hasn't always been recognized

Avicenna (980-1037) - a disciple of Aristotle: they grow within the rocks and resemble bones and plants only by chance

Dogma of the middle ages said that they were created by Satan to confuse us

William Smith (1769-1839) - English canal builder

Spent 24 years mapping canal routes and observing the rocks of the English countryside

First established the relationship between stratified rocks and the fossils they contain

He published the first geological map in 1815

At that time, he failed to recognize the evolutionary significance of the fossils

To him they were essentially just distinctive shapes which allowed him to assign relative orders to the rock units in the area

Since the pioneer work of Smith, most of the world has been mapped (at some scale, at least)

The significance of the fossilized remains has been recognized and used to establish the Relative Time Scale

Paleontology - the study of fossils (or "ancient life")

A study of fossil remains indicates that life forms on earth "have evolved from relatively simple to complex hierarchies of plants and animals"

This evidence was used by Darwin (and others) in the formation of the theory of evolution



Lab Exercise


Using a scale of 1" = 50 million years, construct a Geologic Time Line

4.6 billion years ago, to midnight tonight


Materials Needed:

Butcher paper

Meter stick

Felt pens (several colors


Be sure to include the following "red-letter days" in earth history

4.6 billion years ago - the origin of the earth and solar system

4.1 billion - the first rocks

3.5 to 2.5 billion - large-scale granitic intrusives and the origins of continental crustal material

3.2 billion - oldest evidence of life - bacteria & blue-green algae

2.6 billion to 1.8 billion - banded iron formations

1.8 billion - free oxygen begins building in atmosphere

1.4 billion - eucaryotic cells and enough free O2 to allow aerobic metabolism

600 million - first fossil invertebrates

All periods from Relative Time Scale (Monroe: fig. 1-16, pg. 24)

The Birth of Christ

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