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Geo-101 Week 2 Notes

by: godfreytorrance

Geo-101 Week 2 Notes GEO 101

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Notes for week 2 of Geology 101
Intro Geology
Prof. Yong Zhang
Class Notes
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This 8 page Class Notes was uploaded by godfreytorrance on Monday August 29, 2016. The Class Notes belongs to GEO 101 at University of Alabama - Tuscaloosa taught by Prof. Yong Zhang in Fall 2016. Since its upload, it has received 13 views. For similar materials see Intro Geology in Geology at University of Alabama - Tuscaloosa.

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Date Created: 08/29/16
Geo­101|Chapter 11 a Biography of the Earth 1   Geological Time Table Geologists separate age of the Earth in Eons. i.  Hadean ii.  Archean  iii.  Proterozoic iv.  Phanerozoic    Eras  i.  Paleozoic  ii.  Mesozoic iii.  Cenozoic   Periods i.  Cambian ii.  Ordovician iii.  Silurian iv.  Devonian v.  Carboniferous vi.  Permian vii.  Triassic viii.  Jurassic ix.  Cretaceous x.  Paleogene xi.  Tertiary xii.  Neogene xiii.  Quaternary    Epoch i.  Paleocene ii.  Eocene iii.  Oligocene iv.  Miocene v.  Pliocene vi.  Pleistocene vii.  Holocene    Hadean Eon: Before the rock record    Archean Eon: Birth of the continents and life    Proterozoic Eon: The Earth in Transition    Paleozoic Era: Continents reassemble, and life gets complex    Mesozoic Era: Dinosaurs rule the Earth    Cenozoic Era: The modern world comes to be.  2 .  Hadean Eon Time Interval 4.57­3.85 Ga (Billion yrs) The planet was so hot that its surface was a magma ocean Underwent intense meteor bombardment  A rock record of this Eon does not exist, because the Earth’s  surface may have been partially molten and was pulverized by  meteorites. Internal Differentiation:  i.  Dense iron alloy melted and sank downward (due to  gravity) to form the Earth’s core, leaving less­dense mantle  (ultramafic rock) behind 2 ii.  Formation of the moon iii.  Formation of a toxic atmosphere.  3.  Archean Eon: Birth of the Continents and Life In this Eon (3.85­2.5Ga), the first continent crust (that still  remains) formed, and the first rock record formed.  The atmosphere changed: CO2 is the major component; little  oxygen; so the air was unbreathable. First life: (archaea and bacteria) appeared. 4.  Proterozoic Eon: The Earth in Transition  Time interval: 2.5­0.54 Ga  Cratons formed   Craton: a long­lived block of durable continental crust  (commonly found in the stable interior of a continent)  All Cratons that exist today formed in the Proterozoic Eon  Cratons formed then sutured together to for Supercontinents  Multicellular organisms appeared  The atmosphere began to accumulate significant amounts of  oxygen  This is called the great oxygenation event. With the appearance  of photosynthetic organisms, oxygen began to enter the  atmosphere.   Snowball Earth: At the end of the Proterozoic Eon, radical  climate shifts occurred on Earth. Glacial covered all land, and the entire ocean surface froze.  5. Paleozoic Era: Continents Reassemble, and Life Gets Complex  The early Paleozoic Era: Cambrian­Ordovician Periods (542­444  Ma) 3  Paleogeography  i. The supercontinent Pannotia broke up, yielding smaller  continents.  ii. Epicontinental Sea – is a shallow sea overlying a continent.  Life Evolution   Cambrian Explosion of Life – The remarkable diversification of  life occurring at the beginning of the Cambrian Period  Mass extinction at the end of Ordovician Period due to Ice Age.   The Middle Paleozoic Era: Silurian­Devonian Periods (444­359  Ma)  Paleogeography   Continents continue to reassemble  Examples: Acadian Orogeny & Caledonian Orogeny  Orogeny – A mountain building event.   Land plants and insects begin to appear.  The late Paleozoic Era: Carboniferous­Permian Periods (359­251  Ma)  Continents coalesced to form another supercontinent: Pangea.  6.  Mesozoic Era: Dinosaurs Pangea broke apart, and the Atlantic Ocean formed.  Convergent boundary dominated along the western North  America During the Cretaceous periods, the continents flooded.  The Earth’s climate continued to shift to warmer conditions, and  sea level rose significantly.  Dinosaurs reached their peak of success at this time.  4 Flowering plants and modern fish appeared.  K­T Boundary Event i.  The mass extinction that happened at the end of the  cretaceous period (65 million years ago) possibly due to the collision of an asteroid with Earth. ii.  K stands for Cretaceous and T for Tertiary – Cause  dinosaur extinction.  7   Cenozoic Era – Modern World Comes to Be Paleogeography During the Cenozoic i.  The mountain belts of today rose ii.  Modern plate boundaries became established iii.  Mammals diversified. Recently, ice age glaciers covered  large areas.  Life Evolution i.  Various kinds of mammals filled niches left vacant by the  dinosaurs.  ii.  The human genus, homo, appeared and evolved through the Pleistocene Ice Age. 8   Geologic Time   Geologic Time – The span of time since the formation of the  Earth.  The principle of uniformitarianism – the present is key to the  past. Or in other words, according to this principle, physical  processes (that operate in the modern world) also operated in the  past, at roughly the same rate.   Relative Age – The age of one geologic feature with respect to  another. 5    Numerical Age – The age of one geologic feature given in years.  It is also called the “Absolute Age.” 9   How to Define Relative Age     Principle of Uniformitarianism – Physical processes (we observe  operating today) also operated in the past, at roughly the same  rates.  i. The process that formed cracks today also formed the  mudcracks preserved in the ancient rocks  Original Horizontality – Layers of sediment, when first  deposited, are fairly horizontal, because sediments accumulate on surface of low relief in a gravitational field.   Superposition –   In a sequence of sedimentary rock layers, each  layer must be younger than the one below. This is because a layer of sediment cannot accumulate unless there is already a substrate  where it can collect.  Lateral Continuity – Sediments generally accumulate in  continuous sheets within a given region i. Layers can be continuous over broad areas when the first  deposited. Erosion may later remover part of a layer.  Cross Cutting Relations – If one geologic feature cuts across  another, the feature (that has been cut) is older so younger  features cut older ones.  Baked Contacts ­  If an igneous intrusion “bakes”  (metamorphoses) surrounding rocks, then the rock (that has been  baked) must be older than intrusion.  So the intrusion is  younger.   Inclusion – A rock containing an inclusion (fragment of another  rock) must be younger than the inclusion  so the inclusion is  older than the host rock.   6  Fossil Succession – The assemblage of fossils in strata changes  from base to top of a sequence.  i. Or in other words, fossil species occur in a predictable  order ii. For example, a bed containing fossil F is younger than a  bed containing Fossil A iii. Once a species becomes extinct, it never reappears.  Unconformities – A stratum (plural: strata) 1   Stratigraphic Formations a. A given succession of strata that can be traced over a fairly broad region. b. Stratigraphic Column – Shows the succession of strata in the  region. 2   Stratigraphic Correlations a.  The process of determining the stratigraphic relationship between the strata at one location and the strata at another is called  “correlation.” b. Method 1: Lithologic Correlation – Geologists typically correlate  formations between nearby regions based on similarities in rock  type. c.  Method 2: Fossil Correlation – sometimes we rely on fossils to  define the relative ages of sedimentary units. 3   Geologic Column a.  Geologic column is a composite stratigraphic chart that  represents the entirety of the Earth’s history. b. The column is divided into segments. The largest subdivisions  break Earth history into four eons: the hadean, Archean,  Proterozoic, and Phanerozoic eons. 7 c.  The Phanerozoic eon is subdivided into three eras. We further  divide each era into periods and each period into epochs.  d. The Hadean Eon is not shown because rocks do not preserve a  record of this time interval (i.e., rocks were formed after the  hadean eon.) 4.  How to Determine Numerical Age a.  Isotopic Dating: specifies numerical ages in years b. Geochronology: The overall study of numerical ages c.  Radioactive Decay: Radioactive isotopes decay at a constant rate  characterize by a known half­life. d. What does an isotope date mean?  i.  The isotopic age of a mineral specifies the time at which  the mineral cooled below a closure temperature.  ii.  Closure Temperature: The temperature below which  isotopes are no longer free to move  iii.  If the temperature is higher than the closure temperature,  then isotopes can move freely and therefore change the  isotope ratio, resulting in a meaningless isotopic date. e.  Can we isotopically date a sedimentary rock directly? i.  No.  f.  We can use isotopic dating to determine when an igneous rock  solidified and when a metamorphic rock cooled. g.  To date sedimentary strata, we must examine cross­cutting  relations with dated igneous or metamorphic rock.  8


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