James%20Hutton%20conceived%20of%20the%20Principle%20of%20Uniformitarianism%20at%20Sicar%20Point,%20Scotland%20in%201785.%20Think%20about%20how%20much%20time%20would%20pass%20to%20create%20the%20rock%20record%20shown%20above.%20What%20sequence%20of%20events%20would%20occur%20to%20produce%20the%20above%20record?

1
James Hutton conceived of the Principle of
Uniformitarianism at Sicar Point, Scotland in
1785. Think about how much time would pass to
create the rock record shown above. What
sequence of events would occur to produce the
above record?
2
Layered sedimentary rock is typically deposited
horizontally, but can be deformed by tectonic
processes. Can you think of a depostional
environment where sedimentary layers are not
deposited horizontally?
3
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4
The Principle of Uniformitarianism states that
the present is the key to the past. Those
processes operating at the earths surface today
are inferred to have operated in the past, such
as the mudcracks forming in a playa lake today.
5
The mudcracks shown above formed over 1.1 billion
years ago in a dry lake basin in a location what
is now Montana.
6
Raindrop impressions are preserved in 1.1 billion
year old sedimentary rocks int the Belt Group
rocks of Montana.
7
The Principle of Superposition states that
younger sedimentary rock layers will overlie
older sedimentary rock layers, providing the rock
unit has not been overturned.
8
The principle of cross-cutting relations states
that any structure or rock unit cross-cutting
another structure or rock unit will be younger.
The fault line shown above cross-cuts a glacial
moraine. The seismic event that cause uplift
along the fault post-dates the formation of the
moraine? Based on this same logic which event is
older, the offset along the fault or the stream
deposition that covers the fault.
9
Which formed first and last? The micaceous
schist, the plagioclase dike or the fault that
offsets the dike?
10
Use the principle of cross-cutting relations to
figure out this mess!
11
Which is older? The roof pendant comprised of
contact meta-sedimentary rock or the plutonic
rock?
12
The principle of inclusion states that the
included body will be older than the rock
containing the inclusion (in this case the clasts
within the conglomerate).
13
The principle of faunal succession utilizes
evolutionary changes in the preserved life record
to assign relative ages to rock units.
Trilobites were dominant during the Cambrian
Period (543-490 Ma) and went extinct by 245 Ma.
14
Ferns first evolved during the Carboniferous
Period (363-290 Ma) and were dominant terrestrial
plants. Conifers, flowering plants and grasses
evolved later.
15
During the Mesozoic Era dinosaurs flourished on
the continental land masses. This Allosaurus
footprint impression is found in Jurassic aged
rock.
16
Diplodocus was the largest land animal to walk
the surface of the earth. It measured 90 feet
long from head to tail.
17
Horses evolved 55 million years ago during the
Eocene Epoch of the Tertiary Period.
Warm-blooded mammals dominate the Cenozoic Era.
18
Unconformities represent breaks or missing time
in the rock or geologic record. Unconformities,
such as the angular unconformity shown on the
left, form because of erosional hiatuses or long
periods on non-deposition prior to a subsequent
depositonal event.
19
Three major types of unconformities are
recognized in the field 1. Nonconformity, 2.
Angular Unconformity, and 3. Disconformity. Use
the diagrams of the three types of unconformities
to determine the sequence of events that occur to
form each type of unconformity. Angular
unconformities and nonconformities are the
easiest unconformities to recognize in the field.
Why do you think this is case?
20
What type of unconformity is shown above? How do
you recognize it?
21
What type of unconformity exists at Sicar Point,
Scotland, where James Hutton developed ideas
related to the Principle of Uniformitarianism? Dr
aw the unconformity.
22
What type of unconformity exists at the base of
the Grand Canyon. The lower rock unit is
crystalline plutonic and metamorphic. The rock
unit lying above is layered meta-sedimentary
deposited in coastal setting.
23
You have already determined why disconformities
are the most difficult unconformities to
recognize in the field. What types of geologic
evidence might you use to recognize
disconformities?
24
The Grand Canyon has several unconformities
recognized within its rock record.
25
Five well-known unconformities are shown on the
above cross-section of the Grand Canyon.
26
Geologic Time Scale Do not memorize the geologic
time scale. Know how the major subdivisions are
defined. Why do you think that the more recent
portion of the geologic time scale has greater
detail?
27
Age Equation D Do N(e?t-1) D number of
daughter atoms N number of existing parent
atoms Do number of initial daughter atoms e
exponential function ?? decay constant t time
Radioactive isotopes will decay spontaneously to
form daughter atoms. Radioactive decay is
exponential and constant. Different radioactive
elements will have different decay rates, but the
decay curve will be the same (shown as blue
curve). As radioactive parent atoms decay,
daughter atoms are correspondingly created (shown
as red curve). If you can measure the ratio of
parent to daughter atoms in a isotope system, you
can solve for the age (t). The half life is the
time it takes one half of the existing parent
atoms to decay to daughter atoms.
28
Potassium-Argon dating can be used to date
potassium-rich basalt flows that exceed 300,000
years in age.
29
K-Ar dating was utilized to assign chronology of
early hominid finds in northern Ethiopia.
Paleomagnetic data can be used to fill in gaps
within the chronology.
30
The steep front of this Hawaiian basalt flow
represents an ice-contact front. The basalt flow
abutted against glacial ice and its K-Ar age
provides constraints on the timing of glacial
advance on the Big Island of Hawaii.
31
Up-thrown Block
Down-dropped Block
The range front fault (trace shown by dotted
line) exposed along the eastern Sierra Nevada
cross-cuts a basaltic cinder cone that was dated
using K-Ar dating. How could this age be used to
constrain the uplift rate along this fault?
32
Radiocarbon is first produced in the atmosphere
by collisions of neutrons with nitrogen atoms
(Nitrogen has 7 protons and 7 neutrons in its
nucleus). The neutron will knock out a proton
from the nitrogen atoms nucleus. How many
protons will now be present in the atoms
nucleus? Answer 6. How many neutrons? Answer
8. The atom will now have 6 protons and 8
neutrons in its nucleus and form Carbon-14
(radiocarbon), which is radioactive and has a
excepted half-life of 5730 years.
33
Organic samples are prepared for radiocarbon
dating by combusting or dissolving the organics
and producing CO2 gas. The decay activity in the
CO2 gas will be directly related to the time of
death (age) of the organic material.
34
Radiocarbon dating is useful for assigning ages
to sediment that may incorporate organics during
erosion and deposition, such as this log present
in glacial till.
35
Radiocarbon dating is useful for assigning ages
to young (lt50,000 years old) volcanic ash layers,
such as the Mazama (Crater Lake) tephra shown
above.
36
Radiocarbon dating is useful for capturing
illegal contraband, made from endangered species,
such as this whale bone carving.