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EESA06H3 (240)
Nick Eyles (207)
Chapter 19

Chapter 19 notes

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Department
Environmental Science
Course Code
EESA06H3
Professor
Nick Eyles

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Chapter 19
Time and Geology
James Hutton is regarded as the father of modern geology
He has a theory called uniformitarianism – states that geologic processes operating at present are the
same processes that operated in the past
othe present is the key to the past
othis term is a bit unfortunate, because it suggests that changes take place at a uniform rate
oin some countries, actualism is used instead of uniformitarianism
this term comes closer to conveying Huttons principle that the same processes and
natural laws that operated in the past are those that we can actually observe or infer
from observation as operating at present
it is based on the assumption that physical laws are independent of time and location
dating based on radioactivity allows us to determine a rocks numerical age, also called absolute age
relative time is the sequence in which events took place
Principles Used to Determine Relative Age
contacts are the surfaces separating two different rock types or rocks of different ages
formations are bodies of rocks of considerable thickness with recognizable characteristics that make
each distinguishable from adjacent rock units
onamed after local geographic features
to determine the relationship of geologic events to one another, four principles are applied:
ooriginal horizontality
states that beds of sediment deposited in water formed as horizontal or nearly horizontal
layers
osuperposition
states that within a sequence of undisturbed sedimentary or volcanic rocks the layers get
younger going from bottom to top
if sedimentary rock is formed by sediment settling onto the sea floor, then the first layer
must be there before the next layer can be deposited on top of it
olateral continuity
states that an original sedimentary layer extends laterally until it tapers or thins at its
edges
this is what we expect that the edges of a depositional environment, or where one type
of sediment interfingers laterally with another type of sediment as environments change
ocross-cutting relationships
states that a disrupted pattern is older than the cause of disruption
The Grand Canyon
regional metamorphism took place resulting in the schists of the lower part of the canyon
erosion followed and levelled the land surface
sedimentation followed
these sedimentary layers were subsequently tilted
once again, erosion took place
the lowermost of the currently horizontal layers of sedimentary rock was deposited
each of the layers progressively higher up the sequence formed
finally, the stream eroded its way through the rock, carving the Grand Canyon
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Description
Chapter 19 Time and Geology James Hutton is regarded as the father of modern geology He has a theory called uniformitarianism states that geologic processes operating at present are the same processes that operated in the past o the present is the key to the past o this term is a bit unfortunate, because it suggests that changes take place at a uniform rate o in some countries, actualism is used instead of uniformitarianism this term comes closer to conveying Huttons principle that the same processes and natural laws that operated in the past are those that we can actually observe or infer from observation as operating at present it is based on the assumption that physical laws are independent of time and location dating based on radioactivity allows us to determine a rocks numerical age, also called absolute age relative time is the sequence in which events took place Principles Used to Determine Relative Age contacts are the surfaces separating two different rock types or rocks of different ages formations are bodies of rocks of considerable thickness with recognizable characteristics that make each distinguishable from adjacent rock units o named after local geographic features to determine the relationship of geologic events to one another, four principles are applied: o original horizontality states that beds of sediment deposited in water formed as horizontal or nearly horizontal layers o superposition states that within a sequence of undisturbed sedimentary or volcanic rocks the layers get younger going from bottom to top if sedimentary rock is formed by sediment settling onto the sea floor, then the first layer must be there before the next layer can be deposited on top of it o lateral continuity states that an original sedimentary layer extends laterally until it tapers or thins at its edges this is what we expect that the edges of a depositional environment, or where one type of sediment interfingers laterally with another type of sediment as environments change o cross-cutting relationships states that a disrupted pattern is older than the cause of disruption The Grand Canyon regional metamorphism took place resulting in the schists of the lower part of the canyon erosion followed and levelled the land surface sedimentation followed these sedimentary layers were subsequently tilted once again, erosion took place the lowermost of the currently horizontal layers of sedimentary rock was deposited each of the layers progressively higher up the sequence formed finally, the stream eroded its way through the rock, carving the Grand Canyon www.notesolution.com
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