Revised 8 / 06 (Monroe 6th ed.)

Introduction to Hysterical Geology (Ch. 9)



Introduction to Paleontology

Evolution and natural selection

Evolution and Geologic Time

Relative Age Dating

Stratigraphic Columns

Stratigraphic Correlation



Introduction to Paleontology

Study of earth history based on fossils

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

Used by Darwin (and others) in the formation of the theory of evolution

Fossils have proven to be exciting throughout recorded history (and pre-history)

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: 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

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

He published the first geological map in 1815

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


Several different processes:

Unaltered hard (or soft) parts - pretty rare

Preservation: Rancho la Brea Tar Pits

Amber - like in Jurassic Park

Desiccation - mummies

Frozen - mammoths

Altered hard parts - Your basic fossil

Replacement: usually by calcium or silica

Molds and casts: filled with silt

Trace fossils: tracks, burrows, etc.

Coprolites: fossilized dung

Classification: obviously different creatures so they need different names

Same basic idea as system used in biology

Kingdom, Phylum, Class, Order, Family, Genus, Species, Individual

Used as the basis for the divisions of the relative time scale

Therefore pretty important to geologists

Unfortunately, very spotty record with lots of holes!!

Lots of different species have lived and died on earth throughout geologic history

We're not going to go into great detail, but a few obvious examples include:

Dinosaurs (w/ Jurassic Park film clip?)

Ammonites (key to videodisc)

Trilobites (w/ samples)

Banded Iron Formation (see separate discussion)


Evolution and natural selection

As mentioned earlier...

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

Basic Darwinian theory: explain

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

This has resulted in many similarities between different species

Not unexpected - some things just work well and are in common usage

Such as: 2 eyes, 2 ears so we can calculate distance

Also, similar body parts doing similar things

Called "homologous structures"

Lab: Evidence of Evolution


Evolution and Geologic Time

Life appears to have evolved from simple to more complex forms

Logical progression?

Changing environmental conditions

Addition of free oxygen in the water and atmosphere

Expansion of life into broader niches

Ammonite sutures and water depth

Nature continues to adapt life to the constantly changing surface environment

Has resulted in some amazing patterns in evolution

DIGRESS TO: our BRIEF and LIMITED glimpse of the past!

Lab: Patterns of Evolution


Relative Age Dating

Not much in the way of "Laws" in geology

To review: the classics include...

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

Principle 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

Principle 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

Define tectonics

There are definitely exceptions to this "law"

Principle of Cross-cutting relationships - the zucchini concept

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

In simple terms, nothing can be done to an object which does not exist

Therefore, the thing being acted upon has to be older than the thing doing the acting

Miscellaneous Principles:

Principle of Lateral Continuity

Principle of Inclusions

Principle of Faunal Succession

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


"results from a period of erosion in the geological past during which previously formed rocks were lost, followed by a period of deposition of additional layers of rocks"

Therefore, always indicate 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 uplift and tilting of the sedimentary layers

Lab: Relative Dating - Sequence of Events


Stratigraphic Columns

Click here for a complete discussion from the Ask GeoMan section

Geologists use relative dating techniques to sort out geologic events

DIGRESS TO: stratigraphy, lithology

Prepare localized graphic representations of the stratigraphy

Called stratigraphic columns

Generally follow the rule of superposition

Oldest unit on the bottom

DIGRESS TO : Formations, units, and related subdivisions

There are some accepted symbols used to designate various lithologies and features

DIGRESS TO: stratigraphic symbols

Lots of information contained on a GOOD stratigraphic column


Age relationships

Erosional characteristics


Geologists use these to put together regional correlation of geologic events

And therefore the geologic history of an area

Much more on this later

DIGRESS TO: Marker beds

Lab: Stratigraphic Columns


Stratigraphic Correlation

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 horizons

These are regionally distinctive rock units, fossils, or mineral assemblages

To be a good marker horizon:

Regional in extent

Cover a wide area

Regionally distinctive

Retains its unique characteristics wherever found

Represent a relatively short time

A species which stays the same for 123 million years isn't much help

Ash deposits are excellent examples

Often satisfy all 3 requirements

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: much more on these later

Fossils are the best and most commonly used correlation tool

Rapid evolution of short-lived species works best

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

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

They form the basis for the Relative Time Scale

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

Lab: Facies Relationships



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