Geology 101 Week 2
Geology 101 Week 2 GEO 101
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This 12 page Class Notes was uploaded by Kayla Corbett on Sunday January 31, 2016. The Class Notes belongs to GEO 101 at University of Alabama - Tuscaloosa taught by Dr. Natasha T. Dimova in Fall 2016. Since its upload, it has received 60 views. For similar materials see The Dynamic Earth in Geology at University of Alabama - Tuscaloosa.
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Date Created: 01/31/16
Lecture #3: A Biography of Earth Chapter 11: Geologic Time The span of time since Earth's formation From geological records (analyzes of rocks from the Earth and the Moon), it was estimated that the Earth is 4.6 billion years’ old The Universe • Geocentric theory the Earth is in the center of the Universe • Heliocentric theory the Sun is the center of the Universe Cosmic Systematics Star system: a group of one or more stars, with planets orbiting around them • Example: Solar system, the Sun located in the center Galaxy: a massive group of millions of star systems • Example of galaxy is our Milky Way, Andromeda Universe: includes billions of galaxies In the beginning “The Big Bang” 1. Occurred about 14 billion years ago (Ga) 2. All matter/energy (the Universe) was packed into one point violently exploded 3. Led to creation of elements Evidence supporting “BigBang” theory 1. Galaxies appear to be moving away from each other at speeds proportional to their distance ("Hubble's Law”), i.e. observation supports the expansion of the universe and suggests that the universe was once compacted. 2. We are still “cooling down” 3. The availability of "light elements" Hydrogen (H) and Helium (He) found in the observable universethis is the original material for planet formation Formation and evolution of the Solar System Nebular Hypothesis (Nebular Disk Model) 1. stars form from massive and dense clouds (nebulae) of hydrogen (H ) gas2 2. slowly rotates, gradually collapses and flattens (in a form of a disk) due to gravity 3. Planets form on this disk The mechanisms of planet formation on the disk is not completely clear. So how old is the Earth The Earth was formed about 4.6 billion years ago; We know this from radiometric dating (UraniumLead) of three different materials: 1.) meteoric material from our Solar system; 2.) Moon rocks; 3.) Earth rocks All of them give the same answer! Earth’s interior We know about the structure of the Earth interior: from monitoring earthquake wave propagation through the different layers. The layers have different densities and as a result the earthquakes waves travel with different speed through them. Works just like the sonar for a human body! By definition a galaxy is: A massive group of millions of star systems Approximately how old is the Earth? 4.6 Billion Years The Earths History 1)THE HADEAN EONThe Birth of Earth Major Events 1. Matter accumulates and compacts into dense ball 2. Temperature increased due to compaction and radioactive decay/nuclear reactions 3. The balllike planet partially melted and different layers developed due to different densities of the forming material 4. Collision with other planet resulted in developing the Earth’s satellitethe Moon 5. Atmosphere develops due to major outgassing of formation gases (CH , CO4, H 2) 2 originally incorporated in the planet formation 6. The Earth started cooling down – Hard rocks solidified – Water condensed and started rainfalls – Ocean formed and basic hydrological cycle was initiated 7. NO LIFE YET! 2)THE ARCHEAN EONThe Birth of Continents and First Life Major Events 1. Intensive volcanic activity led to island formation which collided into larger landfirst small continents appeared; 2. First primitive life appeared in the warm oceans. Life probably was sustained in the deep ocean via chemosynthesis. 3. By the end: – First continent formed with evidence for mountain building – Life took place on shallow coastal areasfirst photosynthesizing organisms – Oxygen (O2) started accumulating the atmosphere 3)THE PROTEROZOIC EONThe Birth of Continents and First Life Major Events 1. New continental crust continued to form but slowersmall plates collided in larger continents (crotons) 2. Most of the land was brought together into single supercontinent: Rodinia At the end of the Precambrian: what do we have? • Simple life: single and some multicell organisms • Most of our continents (90%); Rodinia supercontinent • Oxygen and water fairly abundant • That covers about 90% of earths history Specific events/changes during each era! • Paleogeography such as continental configurationcontinents’ break, collision etc. • Life evolution events such as plants and animal’s appearance, disappearance etc. • Other important events such as climate change Phanerozoic Eon is divided into – PALEOZOIC era (542251 Ma)* “ancient life” – MEZOZOIC era (25165.5 Ma) “middle life” – CENOZOIC era (65.5 Matoday) “recent life” – *all numbers are in million years before present – PALEOZOIC: 542 251Ma Early Paleozoic • Breakup of Rodinia supercontinent • Taconic Orogeny: Mountain building event: first stage of Appalachian development • Collision between (what is today) eastern North America and another sliver of land Explosion of Life Starting in Paleozoic, life underwent massive diversification In Oceans: o Shelled animals (gastropods) o Trilobites (first large animals) o Sponges o Corals o First vertebrates (jawless fish) On Land: o Nonvascular Plants – Mosses, liverworts, hornworts o Vascular Plants – Nonseed Plants: Fern, First Vascular Plants – Seed Plants: Conifers, Flowering Plants, First Seed Plants o Ancestral Green Alga Middle Paleozoic • Climate warmed and sea level rose • Acadian orogeny: collision of eastern North America with a small continental mass called Avalon Life during Middle Paleozoic appearance of Plants • Vascular plants – woody tissue, seeds, veins for transporting water, and roots • Large swampy forests (mosses and ferns) Continued Diversity of Life • Bivalves, gastropods • Jawed fish (sharks) • Spiders and insects • First amphibians Late Paleozoic • Significant global cooling and sealevel drop • Formation of Supercontinent Pangaea • Alleghenian orogeny: final development of Appalachians An Interesting Fact Pangea (a supercontinent that formed roughly 300 million years ago) mapped with contemporary geopolitical borders. New Plants and Animal Life • Gymnosperms (“naked seed”) plants: pine trees and spruce • Cycads: palms • Reptiles: eggs with shells; water no longer needed for reproduction End of the Paleozoic Era: Mass Extinction • Appalachian mountain building events; • Pangaea supercontinent • Diversified life (plants and animals) both in oceans and on land. • No mammals yet! largest extinction in history 96% of marine species and 70% of terrestrial species died MEZOZOIC “age of dinosaurs” 251 65.5Ma • Breakup of Pangaea supercontinent: opening of the North Atlantic Ocean • Addition of land to western North America Swimming and Flying Reptiles • Early Mesozoic – Plesiosaurs – Pterosaurs Mesozoic: “Age of Dinosaurs” • Legs positioned under bodies • Warmblooded • Huge (upwards of 100 tons)! Late Mesozoic • Significant warming and sea level rise Laramie orogeny: compression and uplift forming the Rocky Mountains End of Mesozoic • Paleogeography: Pangaea supercontinent broken up • Life: Dinosaurs; large reptiles; small mammals The KT (CretaceousTertiary) Extinction [65 Ma] • Dinosaurs, 90% of ocean species, and 75% of plant species suddenly disappear Review Questions Most of the diversification of life on Earth occurred during which era? Paleozoic Which era is also known as the “Age of Dinosaurs”? Mesozoic The KT extinction (that killed the dinosaurs) was the largest extinction in Earth’s history. False Cenozoic “age of mammals” (65.5Ma to present) Geography – Continents move to current configuration – Himalaya formation Mammals diversified and flourished o Mammoths o Giant Sloths o Giant Bears Cenozoic Climate • Mild climate: broad grasslands developed • Ice Age: – bridge between Asia and North America (Bering Strait) – Migration route for animals and people Evolution of Humans • Australopithecus: first humanlike primate (~4 Ma) • Homo habilis: first human genus; appeared (~2.4 Ma) Evolution of Humans Homo erectus (1.6 Ma)Stone tools Homo Neanderthalensis (500,000 yrs.) Homo Sapiens (150,000 yrs.) Our Species Lecture #4: Patterns in Nature: Minerals Chapter 3: Gypsum (CaSO ∙4 H O2 The cave's largest crystal found to date is 12 m (39 ft.) in length, 4 m (13 ft.) in diameter and 55 tons in weight Calcium sulfate with 2 gallons of water Why study minerals? • Make up of the rocks and sediments • Raw materials for manufacturing chemicals for industrial use • In building machine/tools parts • Energy resourcese.g. uranium • For jewelry • Minerals are the building blocks of rocks What is a mineral? 1. naturally occurring solid 2. formed by geological processes 3. has crystalline structure 4. has defined inorganic composition Naturally occurring • Minerals that are produced in nature, NOT manmade! • Manmade minerals are called “synthetic minerals” Solids • They have their own shape • Difference with liquids and gases which take the shape of the container they are poured into! Crystalline structure • The atoms that the minerals are made of are organized in a specific way. • This specific way is called pattern • Geologists also use the term crystalline lattice • Pattern and crystalline lattice are the same terms! Defined Inorganic chemical composition • There is a chemical formula that can be written to express the chemical composition of a mineral! • The chemical composition is inorganic, e.g. sodium (Na), potassium (K), calcium (Ca) etc. • In contrast, organic molecules are built mostly of carbon (C), hydrogen (H), and oxygen (O); for example, methane (CH , C 4 OH2 5 Composition of minerals Elements • Building blocks of minerals • More than 100 elements Atoms • Smallest particles of matter Rocks/sediments…Minerals...Molecules/Atoms (different chemical elements) Chemistry Refresher Atomic structure • Nucleus – Protons (+) & neutrons (no charge) • Electrons – Surround nucleus () – Located in energy levels shells The structure of an atom Isotopes of the same chemical elements? 14 C (radio carbon14,1/2 = 5730 years): Chemical element: carbon (#6 in the periodic table) Number of protons: 6 Number of neutrons:14 6=8 1C (carbon12, stable): Chemical element: carbon (#6 in the periodic table) Number of protons: 6 Number of neutrons:12 6=6 The same chemical element has the same chemical properties Chemical Bonds Combining 2 or more elements to form a compound. We have several types of chemical bounding: 1. Ionic 2. Covalent 3. Metallic 4. Van Der Waals 1 .Ionic bond • Based on connection between oppositely charged ions • Ion: Atom that has gained or lost electrons. Ion and Anion 2+ Ca3+on-+,tom that has lost electron, has positive charge. For example: Fe , Al , K …etc. Anion- atom (or group of atoms) that have gained electrons (s), i.e. with extra negative charge. For example: SO 4 2; CO 3 Cl , NO ,3PO 4-etc. Ionic Chemical bond: example: NaCl (salt) • Typical for inorganic compounds 2. Covalent bond • Atoms share electrons to achieve electrical neutrality • Covalent bounding: example methane (CH ) 4 molecule molecule Chemical bonds Chemical bonds Compound is a pure substance that can be divided into two or more elements. In this example the molecule of methane and the elements building are: -carbon (C) -hydrogen (H) 3.Metallic bond • Electrons migrate among atoms, good conductivity • Example: copper & gold 4.Van Der Waals bond • Weak attractive force between electrically neutral atoms/molecules • (no electrons available to form bonds) • Example: graphite Chemical reaction: example methane combustion • Process that involves breaking chemical bonds and building new ones Structure of Minerals • Minerals: orderly array of atoms bonded to form a crystalline structure • Different atoms will pack into different arrangements • Orderly arrangement givens minerals symmetry • Example: Salt (NaCl) Polymorphs Minerals with the same chemical composition but different atomic arrangement Graphite Atoms arranged in hexagonal sheets which are connected with week bonds. Diamond Atoms arranged in tetrahedral; strong bonds between them. How do we identify minerals? • by observation • performing simple tests System of several physical properties are used to identify hand samples of minerals called: Primary Diagnostic Properties Diagnostic Properties 1.Crystalline Form • External expression of mineral’s internal structure (i.e. how atoms are arranged) Garnet • dodecahedron Pyrite • cubic 2.Luster • Appearance in reflected light • 2 major categories: Metallic and Nonmetallic Example: Galena displays metallic luster-fresh surface Other descriptive terms for non-metallic minerals include: silky, earthy, glassy, pearly, etc. 3.Color • Generally unreliable for mineral ID; variable due to impurities in mineral chemistry • Colorations of minerals produce gemstones Corundum • Blue = Sapphire (iron) • Red = Rubies (chromium) Beryl • Green = Emerald (chromium) • Blue = Aquamarine (iron) 4.Streak • Color of a mineral in its powdered form • Obtained by scratching the mineral on a porcelain plate • Can be different from color because in powder form, the effect of impurities is reduced Examples: • Hematite: reddish brown • Pyrite: black 5.Hardness • Resistance of a mineral to abrasion or scratching • All minerals are compared to a standard scale called the Mohs Hardness scale 6.Cleavage • Tendency to break along planes of weak bonding • Produces flat, shiny surfaces 7. Fracture • Absence of cleavage when a mineral is broken 8.Specific Gravity • Weight of mineral divided by the weight of an equal volume of water • Avg. = 2.7 g/cm 3 Diagnostic Properties: Other Magnetism • Example: magnetite Reaction to hydrochloric acid • Example: dolomite Double refraction • Example: calcite Taste • Example: halite (NaCl) Smell • Example: sulfur Minerals • Nearly 4000 different minerals • Rock-forming minerals • Only a few dozen members • Made of the most common elements in the Earth’s crust Mineral Groups Silicates (SiO 2: most important mineral group – Very abundant due to large percentage of silicon and oxygen in the Earth’s crust – Silicon-oxygen Tetrahedron: fundamental building block – Four oxygen ions surrounding a smaller silicon ion – Tetrahedron Tetrahedral Forms (combinations) • By combining the SiO tet2ahedra together in different ways, we can make different minerals! Categories of Silicate (SiO )2Minerals • Mafic: – Simpler SiO st2ucture – Dark colored; more dense – Contain iron and magnesium – Examples: Amphibole, Biotite, Olivine • Felsic: Feldspar, Muscovite, Quartz – More complex SiO stru2ture – Light colored; less dense – No iron or magnesium Non Silicate Minerals Less than 10% of Earth’s crust Many non-silicate minerals have important economic value Hematite (Fe O2,3oxide mined for iron ore) Halite (NaCl, halide mined for salt) Sphalerite ((Zn,Fe)S, sulfide mined for zinc ore) Native copper (Cu, mined) Carbonates (CO , mined for cement) 3 Copper Gold
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