Revised 8 / 06 (Monroe 6th ed.)
Orientation and Introduction: Geology 101
Including...
Geologic Time and the Relative Time Scale
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
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?
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
Montserrat
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
...camp 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
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
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
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
"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
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
Unconformities
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
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 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
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
Your Birthday
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