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EESA06H3 (240)
Nick Eyles (207)
Chapter 19&20

Chapter 19 & 20 Textbook Notes

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Department
Environmental Science
Course Code
EESA06H3
Professor
Nick Eyles

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Chapter 19: Time and geology
What is Uniformitarianism?
Uniformitarianism principle that geologic processes operating at the present are
the same processes that operated in the past. The present is the key to the past
(uniform rate)
Actualism physical laws are independent of time and location (same meaning as
uniformitar..)
Geological Time Scale a sort of calander to which events and rock units can be referred
Earth was only 6,000 years old biblical chronology, Noahs flood
features we observed in rocks and landscapes where supernaturally and
catastrophically
James Hutton father of modern day geology
Charles Lyell Principles of Geology book
ogeological features could be explained by present-day processes
How can the Sequence of Past Geological events be determined?
Numerical Age (absolute age) age given in years or some other unit of time
Relative Time the sequence in which events took place (not measured in time units)
ex: Grand Canyon can be analyzed in 4 parts:
ohorizontal layers of rock
oinclined layers
orock underlying the inclined layers (plutonic + metamorphic rock)
othe canyon itself, carved into these rocks
Principles Used to Determine Relative Age
Contacts boundary surface between two different rock types or ages of rocks
Formations bodies of rock of considerable thickness with recognizable
characteristics that make each distinguishable from adjacent rock units, named
after local towns or landmarks
Stratigraphy subdiscipline of geology, that uses interrelationships between layered rock or
sediment to interpret the history of an area or region uses 4 principles:
1)Original Horizontality the disposition of most water-laid sediment in horizontal or
near horizontal layers that are essentially parallel to the Earths surface
2)Superposition a principle or law stating that within a sequence of undisturbed
sedimentary rocks, the oldest layers are on the bottom and the youngest on the top
3)Lateral Continuity principle that states that an original sedimentary layer extends
laterally until it tapers or things at its edges
4)Cross-Cutting Relationships a principle or law stating that a disrupted pattern is
older than the cause of disruption
Other Time Relationships:
Inclusion fragments included in a host rock are older than the host rock
Unconformities - a surface that represents a break in the geological record, with the rock
unit immediately above it being considerable younger than the rock beneath it
1)Disconformity a surface that represents missing rock strata, but beds above and
below that surface are parallel to one another
www.notesolution.com
2)Angular Unconformity an unconformity in which younger strata overlie an erosion
surface on tilted or folded layered rock, implies the following sequence of events from
oldest to youngest:
oDeposition and lithification of sedimentary rock
oUplift accompanied by folding or tilting of layers
oErosion
oRenewed deposition on top of eroded surface
3)Nonconformity an unconformity in which an erosion surface on plutonic or
metamorphic rock has been covered by younger sedimentary or volcanic rock
oCrystallization of igneous or metamorphic rock at depth
oErosion of a least several kilometers of overlying rock (the great amount of
erosion further implies considerable uplift of this portion of Earths crust)
oDeposition of new sediment, thick eventually becomes sedimentary rock, on
the ancient erosion surface
How can rock units be traced from one area to another?
Correlation determining time equivalency of rock units, rock units may be
correlated within a region, a continent, and even between countries
Physical Continuity being able to physically (visually) follow a rock unity between two
places
Similarity of Rock Types same sequence of rocks
Tillites glacially deposited sedimentary rock
Key bed a very distinctive layer
Correlation by Fossils
Paleontologist specializes in the study of fossils
Faunal succession (William Smith) a principle or law stating that fossil species
succeed one another in a definite and recognizable order; in general, fossils in
progressively older rock show increasingly greater differences from species living at
present
Index fossil a fossil from a very short-lived, geographically widespread species
known to exists during a specific period of geological time
Fossil assemblage various different species of fossils in a rock layer
How do we use Relative Dating to Understand Geological Time?
The Standard Geologic Time Scale a worldwide relative time scale based on fossil
assemblages
Relative time scale: 3 eras which are subdivided into periods which are subdivided
into epochs
Precambrian the vast amount of time that preceded the Paleozoic Era
Paleozoic Era (old life) began with the appearance of complex life, as indicated by
fossils
Mesozoic Era (“middle life) dinosaurs became the dominant animals
Cenozoic Era (new life)
oQuaternary Period the youngest geologic period, includes present time
Pleistocene Epoch an epoch of the Quaternary Period characterized
by several glacial ages
www.notesolution.com
Holocene Epoch (Recent)
How can we determine the absolute age of rocks?
Oldest rock from northwest Canada = 4.03 billion years old
Oldest known mineral, zircon, from Austrailia = 4.4 billion years old
Isotopic Dating determining the age of a rock or mineral thru its radioactive elements
and decay products (previously and somewhat inaccurately called radiometric or
radioactive dating)
Geochronologists specialize in isotopic dating
Isotopes atoms (of the same element) that have different numbers of neutrons but
the same number of protons (40K becomes 40Ar, 238U decays to 206U=206Pb)
Radioactive decay spontaneous nuclear disintegration of certain isotopes with
unstable nuclei
oAlpha emission ejection of two protons and two neutrons from a nucleus
oBeta emission release of an electron from a nucleus
oElectron capture proton in the nucleus captures an orbiting electron
19.1 Highlights of the Evolution of Life through Time
Oldest fossils are prokaryotes (lack nucleus) = 3.5 billion years ago
Eukaryotes (single-celled, have nucleus, reproduce sexually) = 1.4 billion years ago
Jellyfish + worms (multicellular) = 700-550 million years ago
Ediacaran biota (soft-bodied animals) = 565-543 m.y. ago found at Mistaken Point
NFLD
Paleozoic greatest mass extinction ever to occur 95% species died, mostly ocean
species
Mesozoic dinosaurs and mammals, second largest extinction 75% of species died
Cenozoic age of mammals, hominids
19.2 Demise of the Dinosaurs Was it Extraterrestrial?
Walter Alvarez and Luis Alvarez hypothesized that extinction was caused by large
asteroid
Marked by (Cretaceous and Tetiary Period) K-T boundary has abundant Iridium
content
Chicxulub crater near the coast of Mexicos Yucatan peninsula
What is Radiocarbon Dating?
Ratio of 12C and14C in organic remains determine the time elapsed since death of
organism
Cosmogenic Isotope Dating (surface exposure dating) uses the effects of constant
bombardment by neutron radiation coming from deep space (cosmogenic) of material
at Earths surface
19.3 Radon, A Radioactive Health Hazard
Radon a odorless, colorless gas, can caused lung cancer, product of 238U decay to
206Pb, has half life of only 3.8 days
where bedrock is granite, gneiss, limestone, black shale, or phosphate rock high
uranium
www.notesolution.com

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Description
Chapter 19: Time and geology What is Uniformitarianism? Uniformitarianism principle that geologic processes operating at the present are the same processes that operated in the past. The present is the key to the past (uniform rate) Actualism physical laws are independent of time and location (same meaning as uniformitar..) Geological Time Scale a sort of calander to which events and rock units can be referred Earth was only 6,000 years old biblical chronology, Noahs flood features we observed in rocks and landscapes where supernaturally and catastrophically James Hutton father of modern day geology Charles Lyell Principles of Geology book o geological features could be explained by present-day processes How can the Sequence of Past Geological events be determined? Numerical Age (absolute age) age given in years or some other unit of time Relative Time the sequence in which events took place (not measured in time units) ex: Grand Canyon can be analyzed in 4 parts: o horizontal layers of rock o inclined layers o rock underlying the inclined layers (plutonic + metamorphic rock) o the canyon itself, carved into these rocks Principles Used to Determine Relative Age Contacts boundary surface between two different rock types or ages of rocks Formations bodies of rock of considerable thickness with recognizable characteristics that make each distinguishable from adjacent rock units, named after local towns or landmarks Stratigraphy subdiscipline of geology, that uses interrelationships between layered rock or sediment to interpret the history of an area or region uses 4 principles: 1) Original Horizontality the disposition of most water-laid sediment in horizontal or near horizontal layers that are essentially parallel to the Earths surface 2) Superposition a principle or law stating that within a sequence of undisturbed sedimentary rocks, the oldest layers are on the bottom and the youngest on the top 3) Lateral Continuity principle that states that an original sedimentary layer extends laterally until it tapers or things at its edges 4) Cross-Cutting Relationships a principle or law stating that a disrupted pattern is older than the cause of disruption Other Time Relationships: Inclusion fragments included in a host rock are older than the host rock Unconformities - a surface that represents a break in the geological record, with the rock unit immediately above it being considerable younger than the rock beneath it 1) Disconformity a surface that represents missing rock strata, but beds above and below that surface are parallel to one another www.notesolution.com 2) Angular Unconformity an unconformity in which younger strata overlie an erosion surface on tilted or folded layered rock, implies the following sequence of events from oldest to youngest: o Deposition and lithification of sedimentary rock o Uplift accompanied by folding or tilting of layers o Erosion o Renewed deposition on top of eroded surface 3) Nonconformity an unconformity in which an erosion surface on plutonic or metamorphic rock has been covered by younger sedimentary or volcanic rock o Crystallization of igneous or metamorphic rock at depth o Erosion of a least several kilometers of overlying rock (the great amount of erosion further implies considerable uplift of this portion of Earths crust) o Deposition of new sediment, thick eventually becomes sedimentary rock, on the ancient erosion surface How can rock units be traced from one area to another? Correlation determining time equivalency of rock units, rock units may be correlated within a region, a continent, and even between countries Physical Continuity being able to physically (visually) follow a rock unity between two places Similarity of Rock Types same sequence of rocks Tillites glacially deposited sedimentary rock Key bed a very distinctive layer Correlation by Fossils Paleontologist specializes in the study of fossils Faunal succession (William Smith) a principle or law stating that fossil species succeed one another in a definite and recognizable order; in general, fossils in progressively older rock show increasingly greater differences from species living at present Index fossil a fossil from a very short-lived, geographically widespread species known to exists during a specific period of geological time Fossil assemblage various different species of fossils in a rock layer How do we use Relative Dating to Understand Geological Time? The Standard Geologic Time Scale a worldwide relative time scale based on fossil assemblages Relative time scale: 3 eras which are subdivided into periods which are subdivided into epochs Precambrian the vast amount of time that preceded the Paleozoic Era Paleozoic Era (old life) began with the appearance of complex life, as indicated by fossils Mesozoic Era (middle life) dinosaurs became the dominant animals Cenozoic Era (new life) o Quaternary Period the youngest geologic period, includes present time Pleistocene Epoch an epoch of the Quaternary Period characterized by several glacial ages www.notesolution.com
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