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Lyell’s views on Geology Sought to explain geologic change by work of natural, observable processes. Based on his views on Hutton’s Theory Granite and basalt were from magma and lava Earth was very old Unlike Hutton: Fossils were important in understanding earth history Uniformitarianism. The uniformity of processes, state and rates of geologic processes of time. Uniformity of laws- natural laws are constant in time and space. Uniformity process- if a past phenomenon can be explained by the result of a process now acting, do not invent an unknown process. Uniformity of rate (gradualism)- pace of change is slow. Uniformity of state (non-progression)- change is not evenly distributed evenly throughout time and space Legacy of Uniformitarinism Uniformity of laws and process are still accepted today. Uniformianty of rate is now not accepted. Processes can be sped up or slowed down. Major events can affect the globe. Uniformity of state is also not accepted. Can have major differences in climate, sea level, tectonic activity in the past. Ex. Glacial ages Lyell made no interpretations about the origin of the earth. Fossils always gave Lyell problems- fossils show major changes through time (extinctions). Modern Concepts of Geology Actualism- only natural laws and principles have been uniform through geologic time. Intensities and kinds of natural processes have been different thro geologic time. Still do not accept: Extremely violent events from supernatural causes. Rigidly uniform steady-state earth. Depositional Environments Sediments and Sedimentary rocks Major Depositional Environments Can be grouped in three categories: Terrestrial- those that occur on land, and include sub aerial and freshwater environments. Coastal- Those that occur at the margin between the land and sea. Marine- those that occur in the ocean. Each depositional environment has a unique kind of sediment that becomes a unique kind of rock. Transgression Sequence- Time 1 Transgression- when a sea or lake expands its extent and the shoreline moves landward.
Regressive Sequence Regression- when a sea or lake reduces its extent and the shoreline moves toward the center of the basin. Geologic Time Methods of Age Dating of Rocks: Relative Age Dating- Sequential ordering of rocks and events. Numeric Age Dating- The assigning of a unit of time for the age of an object or event. Older and Younger Older rocks or events- those which occurred earlier in time. Younger rocks or events- those which occurred later in time. Principles of Relative Age Dating 1 Steno’s Principles Original Horizontality- Sediments are deposited horizontality (deposited in flat layers) Original Lateral Continuity- Sediments originally extended in all directions until they thin to nothing or are limited by the margin of the depositional basin. Superposition- the oldest rocks are on the bottom, the youngest are on top. Recumbent Fold- a fold with a horizontal axis. Principles of Relative Age Dating 2 Hutton’s Principles Crosscutting Relations- any rock body cut by a fault or another rock body is older than the fault or crosscutting rock body. Included Fragments- any fragment of rock in another rock body must be older than the rock body. 1/25/ Unconformities Any contact between two rock bodies that represents a major break in time. Major break in time is more than 1 million years. Includes: Nonconformity- coarse crystalline igneous and metamorphic rocks cut by erosion and buried by sediments. Disconformities- A major gap in time between two parallel sedimentary rock units. Angular Unconformity- contact between a tilted and eroded sedimentary rock sequence covered by flat sedimentary rock units. Faunal Succession Fossils plants and animals succeed each other in a definite and determinable order. Life has undergone through irreversible change through time. Any group of fossils is unique to a particular time. Any period of time can be recognized by its fossils.
Carbon 14 Dating C14 is formed in the upper atmosphere where atoms of Nitrogen are hit by neutrons generated by cosmic rays. C14 combines with oxygen to form CO2. CO2 with the C14 isotopes are taken up by plants during photosynthesis. Animals eat the plant material to take in the C14. Amount of C14 constant while the animal (or plant) is alive. Once the plant or animal dies, then no more C14 enters the organism. Radiometric clock starts. With half-life of 5730 years, can date only back to 70,000 years maximum. Geomagnetism The interaction between the solid inner core and the liquid outer core acts like a dynamo that produces the Earth’s magnetic field. The magnetic field has a pole that is about 10 degrees off of the geographic pole around which the earth spins. Results in: Magnetic Declination- Angle between the true geographic pole and the magnetic pole at any point on the Earth’s surface. Magnetic Inclination- Angle of dip that a magnetized needle will orient across the Earth’s surface. Paleomagnetism Tiny magnetic minerals (typically Magnetite (Fe3O4)) in rocks are orientated to the Earth’s magnetic field at the time of lithification or crystallization. Basalts- abundant iron, lock in when crystallizes. Clastic Sediments- tiny magnetite grains orient then are locked in at lithification. Inclination of these grains reflects where the rocks were relative to the Earth’s equator. Horizontal inclination- Near equator North Arrow dips down- Northern Hemisphere North Arrow inclined up- Southern Hemisphere Geomagnetic Reversals The dynamic relation between the inner and outer core produces alternating strong and weak magnetic fields over long periods of time, and can switch their directions with the current north magnetic pole shifting to the southern hemisphere. These are called magnetic reversals. 2/3/ Continental drift and Plate Tectonics Continental Drift- Theory that the continents have moved laterally over the Earth’s surface. Plate Tectonics- Model by which the Earth’s lithosphere is divided up into large plates that move across the Earth’s surface. New crust is derived from spreading zones. Old crust is recycled back into the Earth at convergence zone. Divergent Boundaries
Where plate spreading occur, and new oceanic crust is added to the plate. The longest mountain ridge is the mid-ocean ridges. Mid oceanic ridges are cut by a graben where the plates split, called a rift. Rifting In Continents As rifts form within continents, and form oceans, the following occurs:
- The continent is bowed upward from upwelling magma
- The two sides separate forming the rift valley surrounded by high plateaus
- The rift valley deepens and extends lengthwise, eventually connecting to the sea
- As the spreading continues, an ocean forms between the two spreading land masses. Convergent Boundaries Where two plates moving in opposite directions meet head on. Subduction zone- one lithosphere plate slides under another plate. Subduction zones are expressed by long deep underwater valleys called trenches typically next to a line of volcanoes, called volcanic arcs. Continental-Oceanic Convergence
Symmetric Ripple marks flow back and forth- formed from waves Asymmetric ripple marks flow in one direction- formed from a current Modern mudcracks- indicate alternating wet and dry conditions Secondary Sedimentary Structures- Nodules Contacts- The surface between two rock layers. Sharp Contact- a very abrupt contact between 2 rock layers. Gradational Contact- a gradual change from one rock type into another. Origin of the Earth and Early Earth History Origin of the Earth 1 In the beginning there was a very large star. Size of this star was between 10x to 50x the size of the sun A red giant or a red super giant- like Betelguese in the constellation Orion
This huge star “burned” Hydrogen, and then Helium by nuclear fusion. H to He to Carbon + thermonuclear energy. Expansion by thermonuclear energy = compaction by gravity. Origin of Earth 2 Eventually the star started to collapse as H and He fuel became low Thermonuclear Energy < Gravity Star fused atoms into heavier and heavier elements H, He, C, O, Si, Fe Origin of these elements that later were in the earth (and in our bodies) Origin of the Earth 3- Supernova Star collapsed even more, so that even Fe started to fuse into heavier elements. Thermonuclear Energy >>> Gravity Star blows itself apart as a Supernova Event. A huge amount of gas is blown out to space Composition of this gas: H= 75%, He= 23%, and remaining 2% is all the other elements. Origin of the Earth 4 The gas expands into space where it is dispersed and becomes very cold. Density very low: 10 atoms/cubic cm; air has 3 billion atoms/cubic cm. Temperature very low, < -173 degrees C or only 100 degrees C above absolute 0. At this temp, the atoms move very slow and clump. Origin of the Earth 5 -Dust clumps together even more from gravitational attraction and becomes a dust cloud or a dark nebula -Enough dust to start blocking light -Because of gravitational attraction from nearby stars and shock waves from exploding stars, the nebula has internal motion- typically a spinning motion. Origin of the Earth 6 -Dark nebula contracts from gravitational attraction of dust. -Density becomes greater and greater as more particles are attracted and come closer. -Spinning dust cloud becomes wheel-like with most dust in the center (the “hub”) and smaller outer disk -Central hub becomes hotter as it contracts. -Materials in the dust start to clump. Origin 7 Contraction of the central hub continues until the temperatures reach about 10 million C. Start to have fusion of H into He. Origin of the Sun, and soon becomes stable. Thermonuclear Energy = Gravity Planets start to form from the clumping of planetismals in the disk.
Events of the Hadean Age of Earth 4.55 Ga Oldest rocks about 4.0 Ga What happened between 4.55 and 4 Ga? Hadean Evidence from the Moon Moon has no rock cycle- preserves ancient features. Features of the Moon: Diameter about ¼ of Earth Average density 3.3g/cubic cm- similar to Earth No plate tectonics Light areas- composed of Ca-rich Plagioclase. Dark areas composed of basalt flows Origin of the Moon 4.4 Ga Mars sized object hits Earth at an angle. The impactor’s and part of Earth’s mantle spewed into space. Ring of debris forms around the Earth and comes together as the moon. Geological Events of the Moon -Moon’s surface is covered by meteorite craters with ages ranging from 4.2 to 3.9 Ga. -Earth probably also was hit by meteorites during this time, but the craters have largely been destroyed by the rock cycle. -Basalt flows on the moon occurred between 3.8 to 3.2 Ga -Little has happened on the moon since this time. Origin of the Earth’s Ocean Water was derived from 2 sources:
- Within the Earth, released from volcanoes as steam.
- From icy comets hitting the Earth Early bombardment of Earth by huge meteorites probably vaporized the first ocean. Once impacts slowed, water began to accumulate. Oldest rocks (Acasta Gneiss) are metamorphic that’s were probably originally marine sediments (3.98 Ga). Origin of the Atmosphere Original Atmosphere was probably composed of gases similar to those released by modern volcanoes.
Original Atmosphere H2O- water CO CH4- Methane H2S- Hydrogen Sulfide SO2- Sulfur Dioxide N2- Nitrogen H2- Hydrogen He- Helium Modern Atmosphere N2- 78% O2- 21% Ar- .9% CO2- .033% Ne- .0018% He- .0005% H2O- variable O2 comes from Photosynthesis- H2O + CO2 sugar + O K40 Ar40 + Ca H2S and SO2, removed by bacteria 2/22/ Hadean Crystals -Grains in quartzite were originally grains in sand. -Zircon crystals (ZrSiO4) formed in older granites, very stable crystals that originally contained Uranium and Thorium. -Dating zircon crystals in sediments, sedimentary rocks or metamorphic rocks date the original granites. -As old as 4.4 Ga. Craton- the large, tectonically stable core of a continent composed of thick Precambrian crystalline rocks. It is made of granite and high grade metamorphic rocks. Shield- Large areas of exposed Precambrian rocks, typically in the center of the craton.
Greenstone Belts -Large basins filled with metamorphosed volcanics and sediments in between granulite plutons. -Named from the abundant green clay- chlorite. -Order of the rocks (top to bottom)
- Sedimentary rocks: Quartz sandstone and Graywacke sandstones Argillites- slightly metamorphic shales and mudstones Banded Iron Formations -Felsic Volcanics- Rhyolites
- Mafic Volcanics- pillow basalts Origin of the Greenstone Belts
- As basins between plutons that were compressed by lateral movements. Require thin crust and high heat flow.
- In basins, formed as huge meteorite impact craters. Beginning of the Proterozoic Mountain Building events- orogenies- that welded the Archean microcontinents together. Continental crust became thicker- probably to the modern average of 35km thick. Plate Tectonics as we know it today started to occur. Beginning of the Wilson Cycle. Wilson Cycle
- Starts with the rifting of a supercontinent to eventually result in an ocean basin.
- Thick accumulation of sediment on the trailing edge of a continent. Passive Margin- the trailing edge of a continent.
- The passive margin became an active margin as the older sediment became compressed during collision with another continent or microcontinent. Form another supercontinent. This cycle typically takes about 600 million years to occur. Accretion to North America during the Proterozoic The Wopmay represents only part of the accretion of the continental crust onto Laurentia. The Superior Province welded with the Wyoming and Hearn Provinces by the Trans-Hudson Orogen ~ 2.5 Ga Added more materials on the south and southeast margins. Central Province- including Colorado, 1.8 to 1.6 Ga Grenville Province- 1.3 to .9 Ga
Precambrian Life 1 Major events in the early history of life Life and the Earth Life occurs on Earth because of the presence of liquid water. Why the Earth has liquid water:
- Earth is not too small, so it can hold an atmosphere.
- Earth is not too large, so it has such a dense atmosphere that sunlight cannot penetrate it
- Earth is in an optimal location from the sun so the temp allows for a liquid water. Early atmosphere and the building blocks of life Early atmosphere and oceans contained: CO SO N CO CH H2S NH H2O All of these are inorganic molecules that are building blocks of life. Anoxic Atmosphere- no free oxygen in the atmosphere. Energy Sources in the Precambrian Earth Heat- from abundant radioactive materials in the Earth. Electricity- Lightning Ultraviolet Radiation- No ozone layer on Earth because the atmosphere was anoxic. Ozone= O Mixture of basic materials- C, N, H, S, P, and liquid H2O and high energy produced chemical bonding of inorganic molecules into organic compounds. Essential Components for life 1
- Proteins- stings of amino acids that act as building materials for life and catalysts in chemical reactions in cells.
- Organic phosphorus compounds- Transform chemical fuel or light energy into compounds, such as sugars, that can be used for energy in a cell.
- Membrane- An enclosing sack that keeps the cell’s components together so the chemicals and interact. Also provides a stable chemical environment that allows chemical reactions to occur. Replicating Compounds Nucleic Acids- Large, complex molecules that can duplicate themselves. (replicating compounds) Are chains of nucleic acids, composed of phosphates, sugars, and nucleotide bases: Adenine-Thymine, Cytocene-Guanine DNA- Contains the inherited chemical code of development. RNA- transforms info from DNA to make proteins and other organic molecules.
Chemosynthesis and Photosynthesis -Chemosynthesis is the ability to construct sugars and other inorganic compounds using external chemical fuels, such as sulfur compounds and methane, as an energy source. -Photosynthesis is the ability to construct sugars and other organic compounds using light as an energy source. Not restricted to sulfur or methane vents. -Source of free oxygen in the atmosphere. Earliest Photosynthesis and Fermentation Earliest bacteria utilizing photosynthesis used sulfur compounds. H2S + CO2 sugars + S (free sulfur) Also broke down sugars using fermentation: C6H12O6 2C2H5OH + 2CO2 + energy Sugar alcohol + carbon dioxide + ATP Autotrophs- those organisms that utilize chemical or light energy to store energy in organic compounds. Heterotrophs- Cant’s make organic compounds so they consume organic material in order to live. Life and the Anoxic World Note that the Photosynthesis utilizing sulfur compounds and fermentation does not utilize oxygen. Free oxygen was poisonous to the first bacteria- anaerobic bacteria. However, sulfur or methane sources are relatively rare on earth. H2O and CO2 are much more abundant on Earth, so photosynthesis processes using these materials have much more resources. Removal of Oxygen in the Precambrian -Oxygen combined with a wide variety of materials dissolved in the oceans during the Precambrian CO, CH4, NH3, reduced Fe, and Si. -Removed O from the environment by forming non-poisonous materials (CO2 and H2O) or precipitated out as sediment (Fe2O3 and SiO2) -This resulted in the deposition of the Banded Iron Formations. Oxygen crisis -At about 1.8 Ga, the materials that the free oxygen combined with in the oceans became depleted. -Oxygen started to build up in the Oceans and atmosphere. -Anaerobic bacteria had to adjust to the increased oxygen levels in the environment. -Many bacteria develop aerobic respiration: Sugars + O2 ENERGY + CO2 + H2O -18X’s more energy is derived from aerobic respiration than from fermentation. Advantages to an Oxygenated World -Utilizing O2 in respiration “recycles” a poisonous waste product. -As O2 builds up in the world, an ozone layer develops in the upper atmosphere. This allowed organisms to come onto land. -Allowed for advanced Eukaryotic cells to form.
Origin of Eukaryotes -Endosymbiosis- Larger bacterial cells engulf smaller bacteria that can respire or are photosynthetic, these smaller bacteria continue to live in the cell producing sugars or having aerobic respiration, eventually becoming organelles.
- The genetic materials of the larger bacterial cell become surrounded by a membrane to form the nucleus.
- Eukaryotic Cell- Has a nucleus and organelles. Development of Metazoans -Metazoans- Multicellular organisms
- Most simple are the multicellular algae, including kelp.
- First multicellular animals were all soft bodied, no hard skeletons
- Found in rocks of youngest Proterozoic.
- All small most less than 2 feet in length. Development of Shells and Skeletons
- Shells provide several advantages to animals.
- Protection from predators.
- Support for muscles and can grow to large sizes.
- Keep the animal above the water-sediment surface.
- Internal skeletons provide support for muscles, and allow for growth into large sizes. Summary of the Events of Precambrian Life
- Inorganic compounds – H2O, CH4, NH3, H
- Simple organic compounds.
- Complex organic compounds.
- Replicating organic compounds.
- Stable organic environment that surrounds the replicating compounds- the cell.
- Photosynthesis and fermentation.
- Aerobic respiration.
- Endosymbiosis to Eukaryotic cells
- Multiple specialized cells- Metazoans.
- Shells and skeletons that are very large in size.
- Nickel and Chrome come from the Precambrian era.
- Uranium- Half of the world’s supply is in Precambrian rocks.
- Gold- Witwatersrand in South Africa; ½ the world’s gold
- Banded Iron Ores- almost all Proterozoic era. NEXT TEST WILL BE ON THE PRECAMBRIAN Continents and Sea Levels through the Paleozoic Laurentia- North America (Missing Florida and parts of the west)- No mountain building at all Baltica- Northern Europe Gondwana- Super continent (Africa, South America, India, Australia, Antarctica, and Arabia) Panthalassic Ocean
Time of deposition of the Banded Iron Formations Alternating bands of iron oxides and Silica. Origin of most of the world’s iron ores. Formed mostly between 2.4 and 1.8 Ga BIF’s very rare after 1.8 Ga. Includes the oldest fossils in the Colorado region- 2.4 Ga stromatolites in the Medicine Bow Mountains, Wyoming. Stromatolites Arcritarchs- First Eukaryote Fossils Oldest fossil record of large, eukaryotic cells: 1.7 Ga. Development of Metazoans Metazoans- multicellular organisms, Most simple are the multicellular algae, including kelp, with oldest fossils ~ 1 Ga Stromatolites start to decline in abundance at 800 Ma, about same time as the 1st^ trace fossils. First multicellualr animals were all soft bodied. Found in rocks of youngest Proterozoic 600 Ma to 541 Ma. First multicellular animals- Ediacara Fauna Earliest Shell, Cloudina, of the latest Proterozoic. Shells and the start of the Phanerozoic Shells and skeletons appeared over a time span of 80 Ma years.
When continents are apart sea level is usually high but when continents are combined (Pangaea) sea level is low. This is a principle of isostacy. Sea floor spreading can also cause a change in sea level. Fast spreading- high water sea level Slow spreading- Low water sea level Glaciations: None: high water sea level Full: low water sea level Summary of Cambrian History Time of widespread marine transgression Sauk Sequence. No major mountain building in Laurentia. ** Review chapter 10 and its figures (basins). Orogeny in Devonian- Arcadian and Caledonian (east coast). Antler Orogeny (west coast). Summary Of Ordovician-Devonain History Mountain building along the modern eastern margin of North America. Taconic Orogeny- Queenston Clastic Wedge Acadian Orogeny- Catskill Clastic Wedge Caledonian Orogeny First mountain building in western North America Antler Orogeny Baltica combines with Laurnetia = Laurussia Large intercratonic basins in the craton Michigan Basin Illinois Basin Williston Basin Mississippian orogeny- Antler (still occurring today) Pennsylvanian Orogeny- Alleghenian, Ouachita, and the ancestral Rockies.
