460:102 Notes Historical Geology Notes : Chp 1 1. Introduction to Geology II: Historical Objectives and Outline

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1 460:102 Notes Historical Geology Notes : Chp 1 1 Chapter 1 Earth as a System Introduction to Geology II: Historical Objectives and Outline Objectives: How our changing views of the planet are affecting the ways we treat it The historical development of the field of geology The development of the basic geologic principles employed by historical geologists. The evolution of the geologic time scale Outline: I. Exploring the Earth s System A. Physical 1. Plate Tectonics, mountains, the rock cycle, chemical reactions, climate B. Biological 1. Bacteria the origin of plants and animals C. Physical and biological components are intertwined 1. Must study system as a whole - not individual components 2. Physical environments influence life creates niches for evolutions, hostile environments 3. Biology can influence physical environment facilitate erosion, change the atmosphere CO 2, II. The Principle of Uniformitarianism A. Uniformitarianism-belief that there inviolable laws of nature that have not change in the course of time. Extends to all sciences. Physics is physics. B. Actualism: The Present is the Key to the past. 1. Differs from Uniformitarianism because it states that the processes observed at work today can be applied to explain the rocks deposited in the past. 2. Exceptions: a. Rocks formed under conditions that no longer exist Banded Iron Formations b. Conditions exist but cannot be observed Depth, metamorphism - Lab results may simulate these conditions. c. Conditions exist at present, but require long time periods to form. III. The Founders of Historical Geology (Most NOT in BOOK)- Forget Plate Tectonics for the time being; What did we know and when did we know it? What led us to the understanding of earth's history that we have at present? What did we overcome to reach our understanding of change? A. Greeks 1. 6 century BC - a. Greek scholars began to record and analyze data within the context of the principles of nature - assumed that the natural phenomena within their world could be understood - search for natural laws concerning the causes and effects b. Observations led to the conclusion of repeatability of processes. Impermanence of details of the Earth's surface (Hutton's Cycles and Uniformitarianism?) c. Examples - stratigraphical and geological - noted that shells not unlike clams and snails that lived along the coasts were found on mountain tops - conclusion ocean extended to the mountain tops

2 460:102 Notes Historical Geology Notes : Chp Herodotus, a Greek historian, concluded in 400 BC that the Med. was at one time more widespread and that the Nile delta was constructed from great volumes of sediment that had been transported and deposited by the Nile River. (Modern sedimentology?) But, he believed most features were the result of sudden, violent processes. 3. Aristotle ( BC) recognized river deposits and realized that fossil seashells from rocks were similar to those found on the beach, indicating the fossils were once living animals. He deduced that the positions of land and sea had changed and thought these changes occurred over long periods of time. 4. Eratosthenes (250 BC) calculated the circumference of the Earth by measuring noontime shadows at two localities of different latitude. He extrapolated the distance from his reference points at Syene and Alexandria in Egypt and determined Earth's circumference to be ~40,000 km, a remarkably accurate estimate and major scientific accomplishment. (40,045km) B. Romans - Grecian theories of scientific inquiry transcended time and culture and were inherited by Roman scholars. 1. Pliny the Elder (23-79 AD) reached similar conclusions as those of the Greeks concerning the distribution of land and sea; modern and fossil shell comparisons, volcanic eruptions (documented Vesuvius), earthquakes and floods. 2. Augustine of Hippo ( AD) stated that the crucifixion was a unique event from which all events could be measured, thus initiating the BC/AD time scale. Note: modern archaeologists sometimes use a bce/ce scale to denote "before common era" and "common era". C. --- The Dark Ages (~ AD) --- Decline of the Roman Empire - Principle of uniformity of nature's processes, along with scientific inquiry suffered a critical blow - The DARK AND MIDDLE AGES. For 1000 years, Religious dogma held sway and any departures from the structures of the time was considered a serious offense. D. --- Printing Press invented (1450) [Renaissance begins] --- The Renaissance - advance in many scientific fields - development of scientific principles - Copernicus, Kepler and Galileo put the Earth in a new cosmic context (Astronomy). Geology - another story - religious climate still limited advances in geology - the science of the Earth itself. Genesis portrayed an Earth that was 6000 yrs. old. Creationists considered the Earth as stable since the Noachian flood catastrophe. 1. Leonardo da Vinci ( ) recognized that material carried by rivers to the sea was eventually compacted into sedimentary rock and later uplifted to form mountains. He concurred with Aristotle's view that fossils were the remains of ancient life. As a byproduct of his engineering work on canals and rivers, he studied the deposits of the Po River and concluded that they must be at least 200,000 years old. He surmised that the whole of geologic time must be much longer. 2. James Ussher ( ) was the first to estimate the age of the Earth using genealogies of the Bible. Ussher stated in 1650 that the Earth was created on October 22, 4004 BC. This date was later reproduced in many editions of the Bible and was incorporated into the dogma of the Christian church. For nearly a century thereafter, it was considered

3 460:102 Notes Historical Geology Notes : Chp 1 3 heresy to assume that Earth and its puzzling geologic features were more than ~6000 years old. Thus, a very young Earth provided a basis for most chronologies until the 18th century. 3. Nicholas Steno or Neils Stensen (Danish physician, ) a. Studies of Italian geology - settled in Florence Italy - Physician to the Grand Duke of Tuscany - ample time to explore and follow interests b. Developed basic geologic principles 1. Superposition - observed the layered strata in Tuscany as he tramped around the countryside; witnessed the process of deposition of layers in an aqueous medium. When Layers formed only the fluid was overlying. Therefore, no overlying layers could have been present when the lower layers were formed. Superposition! The oldest layer is at the bottom and successively higher layers are successively younger in an sequence of undisturbed strata. Probably not the first to recognize layering and may not have been the first to conclude Superposition. But he was the first to articulate this and put it into perspective. 2. Original horizontality - settling particles under the influence of gravity - the layering should form parallel to the surface on which it was accumulating; important for understanding tilted strata - revealed an episode of crustal disturbance 3. Original lateral continuity - as originally deposited, strata extend in all directions until they terminate by thinning at the margin of the basin, end abruptly against some barrier, or grade laterally into a different kind of sediment. c. First to study stratigraphy in an organized way E. First attempts at Subdivision: An Economic Incentive 1. During the Renaissance, interest in mining and mineralogy grew significantly, Industrial Revolution. George Bauer, a.k.a. Agricola, became the Father of Mineralogy, wrote extensively on mineral classification and mining activity. From this, mining academies were started. Needed a scheme to understand the origin, occurrence and relationship of ore minerals to help locate and exploit other regions with minerals. Economic incentives vs. pure scientific endeavor? Superposition to an extreme - stratified low lying rocks formed the foothills and igneous and metamorphic rocks form the cores - All crystalline rocks formed at one time and all sedimentary rocks formed later. Superposition is a good descriptive generalization applicable to individual mountain belt but was stretched to a faulty unfounded principle which was perpetuated through geology 2. Abraham Gottlob Werner (German, ) a. Professor Mineralogy, Freiberg Mining Academy b. Internationally known - first great synthesizer of geologic knowledge - Carried the idea that all crystalline rocks formed at one time to an extreme. Zealously nurtured the idea that all rocks of the Earth s crust, regardless of composition were precipitates of the world encompassing primeval ocean. Hot and steamy ocean full of dissolved minerals needed to form the rocks. As the ocean shrank (subsidence and cooling), it left behind the precipitated layers arranged in superpositional order. Each layer was considered to have its own composition and be of the same age everywhere. "neptunism" because water was the forming agent. 3. Advocated "neptunism" theory and a "universal sea" to explain stratigraphy 4. Developed a four-fold classification of rock ages a. Primitive Series - Granite at the bottom followed by gneisses, schists, and other crystalline rocks

4 460:102 Notes Historical Geology Notes : Chp 1 4 b. Transition Series, slates, graywackes, quartzites, and limestones. Some were fossiliferous and considered to be the early forms of life. Transition from uninhabitable to habitable. Werner considered that the Primitive and Transition series to have covered the entire surface at one time. c. Secondary Series, fossiliferous succession of sandstone, limestone, slate, and coal formed by chemical precipitation as the ocean shrank to its size. Some surface reworking by running water. d. Alluvial rocks topped the sequences, sand, gravel, clay, peat, ash Neptunism was appealing because it was consistent with the biblical account of the creation. Young Earth yrs. old. Problems - where did the water go? Same origin for basalt as for shales, limestones etc. J.F. D Aubisson de Voisins proved volcanic origin of basalts 3. James Hutton (Scottish, ) Physician turned geologist. Not bound by the arithmetic of the biblical chronology. Demonstrated that rock units and relationships were not worldwide, but regional. Conflict - origin of basalt in a Primitive Series - Neptunist - Ocean ppt. Arduino appreciated the igneous origin of basalts when he named the volcanic subdivision of the Tertiary Series. Hutton demonstrated that basalt could form as an intrusive body. Cross cutting granite dikes through stratified rocks led him to igneous origin and that they were molten when they forced their way into fissures. Plutonists. a. Dynamic/cyclic concept of earth history - recognized that every rock formation no matter how old, appeared to have been derived from other rocks, still older rocks. Earth is always changing. Succession of Worlds. Destruction through erosion and weathering. b. Principle of Uniformitarianism (Actualism) - Hutton was convinced that the geologic processes in the past were no different from the present. No powers that are not natural to the globe, no action to be admitted of except those of which we know the principle, and no extraordinary events to be alleged in order to explain a common appearance. Hutton never used Uniformitarianism (William Whewell). The present is the key to the past Sir Archibald Geike. c. First great geology text: Theory of the Earth (1785) - important book but his writing was cumbersome and filled with too many details which obscured the thrusts of his arguments. John Playfair a friend and colleague of the Royal Society assumed the task of clarifying Hutton s idea. Published a brilliant summary in Illustrations of the Huttonian Theory of the Earth. Playfair - Amid all the revolutions of the globe the economy of Nature has been uniform and her laws are the only thing that have resisted the general movement. The rivers and the rocks, the seas and the continents have changed in all their parts; but the laws that describe those changes, and the rules to which they are subject, have remained invariably the same. d. Concept of immense length of geologic time - Recognized the importance of unconformities and cross-cutting features. The result, therefore, of our present inquiry is that we find no vestige of a beginning and no prospect of an end. Irreconcilable with 6000 yr. old earth. Hutton credited with idea of Deep Time. Father of Modern Geology even though much of his book was theoretical and based too little on field evidence. Through time Biblical account of age of Earth faded, Neptunism and young Earth lost ground because it was contradicted by too many data.

5 460:102 Notes Historical Geology Notes : Chp Charles Lyell (English, ) 1. Advocate and author exposing views of ancient earth history and Uniformitarianism - collection, organized and presentation the data in support of Uniformitarianism. Hutton s view of the Earth and Playfair s clarification were slow to take hold. Lyell s crusade: a) establishment of uniformitarianism at he expense of catastrophism as the acceptable philosophy for interpreting the history of the Earth b) establishment of geology among the sciences as a discipline based on inductive principles 2. Author of important text: Principles of Geology (1830) 3. Synthesizer of stratigraphy who developed the first geologic time scale- Founded Modern Historical Geology and reintroduced Unlimited time. Unlike Hutton, Lyell was a historian who realized the primary task of geology was the unraveling of the Earth events in time. Used Faunal succession. Successive cycles 4. Principles of Cross-cutting relationships and inclusions 5. Developed concept of relative age dating and sequence of events IV. The Nature and Origin of Rocks A. Igneous 1. Texture a. Intrusive- coarse grained b. Extrusive fine grained 2. Composition a. mafic - dark colored - Basalts b. intermediate c. sialic - Light colored - Granites B. Sedimentary 1. Clastic - grain size Largely a function of energy of environment a. sandstones b. siltsone c. claystone 2. skeletal remains - Limestone 3. Chemical - evaporites C. Metamorphic - Alteration - metamorphosis - temperature and pressure 1. grain size - slate-phyllite-schists- gneiss 2. quartzite and marble V. The Rock Cycle A. All rocks are subject to change after they form B. Sedimentary 1.Unconformity - a surface between sedimentary strata that representd an interval of time during which erosion occurred 2.Angular unconformity - unconformity where the older layers were tilted 3. Disconformity - surface where little was disturbed, perhaps difficult to see 4. Nonconformity unconformity on top of eroded crystalline rocks. VI. Global Dating of the Rock Record A. Relative ages 1. Fossils and Markers 2. Cross-cutting and Inclusions B. Absolute ages C. Geologic Time D. Development of the Time Scale

6 460:102 Notes Historical Geology Notes : Chp 1 6 VII. Imaging the Earth Largely developed by Studying Earthquakes A. The Density Gradient 1. Crust - Outer Skin 2. Mantle Ultramfic rocks 3. Core Inner sphere of Fe-Ni 4. Mohorovicic Discontinuity B. Lithosphere vs. Asthenosphere 1. Plates VIII. Plate Tectonics A. Plate Movements 1. Ridges, Subduction Zones and Transform Faults B. Volcanoes at Plate Boundaries C. Mountain Building IX. The engine of Plate Tectonics A. Heat 1. Convection, Conduction and Radiation B. Plate Tectonics and the Rock Cycle X. The water Cycle A. Reservoirs 1. Ocean = 97.25% 2. Glaciers = 2.05% 3. Groundwater = 0.68% 4. Lakes = 0.01% 5. Soils = 0.005% 6. Atmosphere = 0.001% 7. Rivers = % 8. Land Plants = % B. Interactions with the Rock Cycle 1. Weathering, Erosion, Deposition 2. Evaporation 3.