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Transcript
Advanced structure of the Earth By Doba D. Jackson, Ph.D. Associate Professor of Chemistry & Biochemistry Huntingdon College Outline of Lecture 1 • Part I: Matter & Matter changes – – – – – Natural Science-Physical Science Physical & Chemical Properties Elements of Nature Temperature, Pressure Physical States of Matter • Part II: Origin of the Universe and matter – Big Bang (video) – Formation of atoms, elements – Formation of galaxies, our solar system Outline of Lecture 1 • Part III: Structure & Components of Earth – – – – – – – – Earth’s Core Earth’s Mantle Earth’s Crust Lithosphere Asthenosphere Rock Cycle (Sedimentary, Metamorphic, Igneous) Plate Tectonic Theory (intro) Geologic Time (intro) Plate Tectonic theory • Plate tectonic theory states that the lithosphere is divided into rigid plates that diverge, converge, or slide past each other as they move over the asthenosphere. Plate Tectonic theory The movements of the plates and the interactions of plates along their boundaries cause volcanic eruptions, earthquakes, the formation of mountain ranges and ocean basins, and recycling of rock material. The Rock Cycle • What is a rock? – A rock is an aggregate of minerals. Granite Slate Limestone Quartzite Conglomerate Gneiss The Rock Cycle The Rock Cycle • What are the characteristics of each of the three major rock groups? • Igneous rocks result from the crystallization of magma or the consolidation of volcanic ejecta. The Rock Cycle • Sedimentary rocks are typically deposited in layers formed by the: – consolidation of rock fragments – precipitation of mineral matter from solution – compaction of plant or animal remains The Rock Cycle • Metamorphic Rocks- that result from the alteration of other rocks; – Metamorphic rocks usually form beneath Earth’s surface, by • Heat • Pressure • Chemically active fluids. The Rock Cycle connects the internal and external processes of the earth Plate Tectonic theory • Plate tectonic theory states that the lithosphere is divided into rigid plates that diverge, converge, or slide past each other as they move over the asthenosphere. Plate Tectonics? Plate interaction is a major factor that determines when, where and what kind of rock develops. Geological Time Radioactive Decay Example 14 C 6 Parent 14 N 7 Daughter + Nt Equation: Ln = -kt N0 -N is the number of radioactive atoms per minute per gram Carbon -N0 is the initial number of radioactive atoms per and per gram Carbon -k is the decay constant for carbon -t is the age of the sample 0 β -1 Half-life 14C is 5730 years Radioactive Decay Example 14 C 6 Parent 14 N 7 Daughter + Nt Equation: Ln = -kt N0 -N is the number of radioactive atoms per minute per gram Carbon -N0 is the initial number of radioactive atoms per and per gram Carbon -k is the decay constant for carbon -t is the age of the sample 0 β -1 Half-life 14C is 5730 years Radioactive Dating Methods Parent 147Sm Daughter Half-life 143Nd 106 billion years 87Rb 87Sr 238U 206Pb 40K 40Ar 235U 207Pb 234U 230Th 235U 231Pa 14C 3H Samples Used Rocks 50 billion years Rocks 4.47 billion years Rocks 1.3 billion years Rocks 14N 704 million years 80,000 years 34,300 years 5,730 years Rocks Rocks Rocks Organic Fossils 3He 12.3 years Organic Fossils Geological Time • Eon- Time periods around .5 to 1 billion years. • Era- Time periods between 100 million and 500 million years. These occur within Eons. • Periods- Time periods between 10 million and 100 million years. • Ages- No Early Evidence for Plate Tectonics: Continental Drift Hypothesis The idea that continents have moved in the past is not new and goes back to the first maps, in which one could see that the east coast of South America looks like it fits into the west coast of Africa. Pangaea Supporting evidence for a Continental Drift 1) Continental Fit- Outlines of coasts closely approximate each other. 2) Fossil Evidence- Similar extinct plant and animal fossils on different continents. 3) Glacial Evidence- Similar leftover tills in rocks on different continents. 4) Rock layers sequences in different ages. Scientists responsible for Continental Drift hypothesis • Abraham Ortelius (1596)- developed the first map and theorized that continents drifted across oceans to their present positions. • Edward Suess (1885)- First to propose that continents were connected based on fossil evidence. Named southern continents as Gonwana. • Alfred Wegener (1915)- credited for the continental drift hypothesis. (Named supercontinent Pangaea) • Harry Hess (1962)- revised the continental drift theory into the Plate Tectonic theory. Abraham Ortelius developed the first map of the world Ortelius was a world renown English geographer in his day. He spent his life making regional and continental maps. Through lots of partnerships, and traveling, he was able to develop the first maps of the world. Latin: Theater of the World He suggested after publishing his 33rd map of the world: “The America’s may had originally been joined together but later drifted away by earthquakes and floods” in 1578 Edward Suess 1831-1914 Edward Suess was the first to provided fossil evidence for the continental drift hypothesis Glossopteris flora- The fossil flora that succeeds the Permian glacial deposits of South Africa, Australia, South America, and Antarctica. It grew in a cold, wet climates. Plants with elongate, tongueshaped leaves dominated the southern flora. Austrian Geologist Edward Suess proposed the southern continents were once connected and used the term Gondwana Alfred Wegener noted similarities of rock sequences for southern continents Glacial Striations as evidence for continents drifting Glacial striations are scratches or gouges cut into bedrock by glacial (ice) abrasion. Glacial striations form when ice picks up small rock fragments. When the ice forms or melts on rock, picks up small pieces of rock or sand and it scratches the surface of the rock as it moves across it. Glacial striations are usually multiple, straight, and parallel lines . Glacial Striations in bedrock found in South America, India, South Africa and Australia Arrows on each picture represent the direction of melting of the ice Notice India’s presence The directions of the glacial striations indicate that the southern continents were closer together at the south pole. Setback in the Continental Drift Theory • None of the scientist could reasonably explain How could the continents drift? Continental Shelf- region off the ocean boundary where the seafloor is shadow. Mapping of seafloor’s found no evidence of continents drifting on liquid water. Paleomagnetism studies of the 1950’s revived the debate Where and how is Earth’s magnetic field generated? - Electrical currents in the (liquid Iron) outer core probably generate Earth's magnetic field. The lines of magnetic field surrounding Earth resemble those of a bar magnet. Paleomagnetism Rocks North Paleomagnetism is the reminant magnetism of ancient rocks. Ancient rocks showed a different orientation of its magnetic field. Lodestone, Magnetite, Maghemite- iron containing mineral rocks with magnetic properties (Fe3O4). South Paleomagnetic data can be used to construct the positions of early continents Rocks analyzed during the same time period gave different positions of their magnetic poles. Scientists assume the position of the magnetic pole has not changes over millions of years, but the position of the continents have changed. Paleomagnetic data can be used to construct the positions of early continents Rocks analyzed during the same time period gave different positions of their magnetic poles. Scientists assume the position of the magnetic pole has not changes over millions of years, but the position of the continents have changed. Discovery and mapping of the Mid-Atlantic Ridge Paleomagnetic studies revealed the existance of Earth’s magnetic field reversals Paleomagnetic studies revealed the existence of Earth’s magnetic field reversals in lava flows Henry Hess proposed the theory of Seafloor Spreading in 1962 • What is the theory of seafloor spreading? – He suggested that the seafloor separates at oceanic ridges, where new crust is formed by upwelling magma. – As the magma cools, the newly formed oceanic crust moves laterally away from the ridge. How was the theory of seafloor spreading confirmed? Another confirmation of Seafloor Spreading theory is the age of rocks on ocean floor Sea floor spreading is confirmed by – the ages of fossils in sediments overlying oceanic crust – radiometric dating of rocks on oceanic islands and floors. Red- present to 48 mya Yellow- 48-68 mya Green 68-155 mya Blue- 155-180 mya Model for How Seafloor Spreading Occurs Plate Tectonics: A Unifying Theory • Overwhelming evidence in support of plate tectonics led to its rapid acceptance and elaboration since the early 1970's. – The theory is widely accepted because it explains so many geologic phenomena. – Plate Tectonic Theory encompasses the Seafloor Spreading Theory with thye existance of Earthquakes and Volcanism. – For these reasons, it is known as a unifying theory. What are the main tenets of Plate Tectonic Theory? The Three Types of Plate Boundaries • Divergent Plate Boundaries- Spreading ridges that occur where new lithosphere is forming and older lithosphere is separating away. • Convergent Plate Boundaries- Boundary where older crust is destroyed and recycled to keep the surface area of the earth the same. • Transform Plate Boundaries- (or Transform faults)- Changes one type of motion between plates to another type of motion. • History of Divergent Boundaries – Divergent boundaries form when rising magma beneath a continent pushes crust up to form mountains, faults, valleys and volcanic activity – As more continental crust is broken, valley’s form with volcanic activity. • History of Divergent Boundaries - As more continental crust is broken, valley’s form with volcanic activity. - (East African Rift Valley) - Continued spreading splits apart the continent and a seaway develops (Red Sea) • History of Divergent Boundaries - Continued spreading splits apart the continent and a seaway develops (Red Sea) - Continued spreading, a oceanic ridge system develops (Mid-Atlantic Ridge) East African Rift Valley may be the future Diverging plate boundary Red Sea may be the next MidAtlantic Ridge system The Three Types of Convergent Plate Boundaries • Convergent boundaries are places where two plates collide and one plate is subducted into the asthenosphere. • Oceanic-oceanic boundary is where two oceanic plates collide, one ocean plate will subduct beneath the margin of the other plate. • Oceanic-continental boundary is where an oceanic plate and a continental plate collide, the oceanic plate will subduct. • Continental-continental boundary occurs when two continents collide Oceanic-Oceanic Convergent boundaries – One oceanic plate is subducted beneath the other and a volcanic island arc forms on the non-subducted plate – An oceanic trench forms parallel to the volcanic island arc where the subduction is taking place. – The volcanoes result from rising magma produced by the partial melting of the subducting plate. Oceanic-Continental Convergent Boundary – An oceanic plate and a continental plate converge, with the denser oceanic plate being subducted under the continental plate. – Just as with an oceanic-oceanic boundary, a chain of volcanoes forms on the nonsubducted plate. Continental-Continental Plate Boundaries – Two continents converge and the ocean floor separating them is subducted, resulting in a collision between the two continents. Neither plate will subduct. – When the two continents collide, they are welded together to form an interior mountain chain along a zone marking the former site of subduction. Transform Plate Boundaries • Transform boundaries (also Transform Faults) are boundaries along which plates slide laterally past each other, which change one type of motion between plates into another type of motion. Types of Plate Boundaries Introduction to Chapter 3 • What is a mineral? A mineral is – Naturally – Inorganic – Crystalline solid – Characteristic physical properties – Specific chemical composition. Matter, Atoms, Elements, and Bonding • What are the atomic number and atomic mass of an atom? – The number of protons in an atom’s nucleus determines its atomic number, whereas an atom’s atomic mass number is the total number of protons and neutrons in the nucleus. Matter, Atoms, Elements, and Bonding • Chemical bonding – Atoms are joined to one another by forces known as bonding. – Atoms of different elements which are bonded to one another form compounds. Types of Chemical Bonds • Ionic Bonds – Ionic bonds form when ions with opposite electrical charges attract one another Types of Chemical Bonding • Covalent Bonds – Covalent bonds atoms share electrons. Native Elements vs Minerals By definition native elements are made up of only one chemical element, such as: – Gold (Ag) – Silver (Ag) – Aluminum (Al) – Copper (Cu) – Diamond (pure C) Elements of the Earth’s Crust • Why are there so few common minerals? – Even though there are 92 naturally occurring elements, only 8 of them are very common in Earth’s crust. – Most common minerals are made up of oxygen, silicon, and one or more other elements.