GSU GEOL 1122K - Geology Exam 2 Textbook (31 pages)

Previewing pages 1, 2, 14, 15, 30, 31 of 31 page document View the full content.
View Full Document

Geology Exam 2 Textbook



Previewing pages 1, 2, 14, 15, 30, 31 of actual document.

View the full content.
View Full Document
View Full Document

Geology Exam 2 Textbook

155 views


Pages:
31
School:
Georgia State University
Course:
Geol 1122k - Introductory Geosciences Ii
Unformatted text preview:

Chapter 2 presents details about the Earth s magnetic field that build upon what you learned in Chapter 1 Although the Earth s magnetic field has only a North and South pole the two poles a dipolar field periodically alternate their locations while remaining near the Earth s axis of rotation You also learn that when igneous rocks cool they record the direction and dip of the magnetic field in existence at that time paleomagnetism and that scientists can later tease this information out of rocks You learn how scientists began to couple isotopic age dating of rocks with the rocks paleomagnetic signatures to build detailed paleomagnetic histories Scientists then discovered that each continental block had a unique paleomagnetic record suggesting differing and confliction locations of the Earth s magnetic poles in rocks of the same age Because physicists were quite certain that the Earth s magnetic field has always been dipolar this led scientists to postulate that over time the continents might have drifted over Earth s surface taking independent paths like hockey players in an ice rink The major features of the ocean are discussed and how patterns of earthquakes heat flow crustal age paleomagnetism and thickness of sea floor sediment led several scientists in the early 1960s to conclude that new crust is made at mid ocean ridges flows sideways away from the ridges and is recycled down into the mantle at deep sea trenches During the 1960s the idea of oceanic crust being made and destroyed became accepted as a means to explain Wegener s continental drift and many other geologic phen omena You are introduced to the lithosphere and asthenosphere the basic definition of a tectonic plate and the three basic types of plate boundaries divergent convergent and transform You learn about rifting of both oceanic and continental crust at divergent boundaries why only oceanic crust is recycled subducted into the mantle and that transform boundaries generally lack volcanism You also learn about triple junctions and hot spots Each of these concepts is reinforced with the study of actual boundaries and features of each type You also learn about the forces that move plates both ridge push and slab pull The chapter concludes by showing you GPS data which was not available to scientists until the 1980s has become proof that discrete zones of the Earth s surface plates move in different directions and supports the theory that crust is made and destroyed at some plate boundaries Alfred Wegner died in 1930 disgraced by most geologists for his ideas that continents had drifted through time Had Wegener lived another 40 years he likely would have been thrilled by the new data collected about the Earth and might like the glaciologist Louis Agassiz who we study in chapter 18 have slowly won over the opinions of his colleagues Chapter 2 Textbook Annotations 2 1 Introduction o Alfred Wegener thought that continents once fit together like pieces of a giant jigsaw puzzle to make one vast supercontinent This is known as Pangaea o Pangaea was later fragmented into separate continents that drifted apart moving slowly to their present positions this is known as continental drift o In 1960 Harry Hess and Robert Dietz proposed that as continents drift apart new ocean floor forms between them this is called sea floor spreading o As the continents move toward each other when the old ocean floor between them sinks back down into the Earth s interior a process known as subduction o Earths lithosphere the outer rigid shell consist of about twenty distinct pieces or plates that slowly move relative to each other This is knowing as plate tectonics o The theory of plate tectonics The plate movements that build regional geological features This is how we can successfully explain many geological phenomena 2 2 Wegener s Evidence for Continental Drift o Pangaea existed until the end of Mesozoic Era 251 65 million years ago Pangaea then broke apart and the land masses moved away from each other to form the continents that we see today The fit of the continents o All the continents could be joined with remarkably few overlaps or gaps to create Pangea o Wegner concluded that the fit was too good to be a coincidence and thus that the continents once did fit together Locations of past glaciations o Glaciers are rivers or sheets of ice that flows across the land surface o As the glacier flows it carries sediment grains of all sizes clay silt sand pebbles and boulders o Grains protruding from the base of the moving ice carve scratches called striations into the substrate o When the ice melts it leaves the sediment in a deposit called a till that buries striations o Thus the occurrence of till and striations at a location serve as evidence that the region was covered by a glacier in the past By studying the age of glacial till deposits its been determined that large areas of the land were once covered by glaciers during the time known as the ice ages One of these ice ages occurred from 326 267 million years ago near the end of the Paleozoic Era The distribution of climatic belts o Studied sedimentary rocks that were formed at this time for the material making up these rocks can reveal clues to the past climate Equatorial late Paleozoic sedimentary rock layers include abundant coal and the relicts of reefs Subtropical late Paleozoic sedimentary rock layers include relicts of desert dunes and deposits of salt The distribution of fossils o Continents provide homes for different species o Many kinds of plants grow only on one continent Thus animals and plants evolved independently on different continents When all continents were in contact land animals and plants could have migrated among many continents o The distribution of fossil species required that the continents have to have been adjacent to one another in the late Paleozoic and early Mesozoic Era Matching Geologic Units o If the continents had been joined to create Pangaea in the past then these matching rock groups would have been adjacent to each other and thus could have composed 2 3 Paleomagnetism and the Proof of Continental Drift o Magnetite an iron rich mineral that aligns with earth s magnetic field lines o Several rock types contain tiny crystals of magnetite or other magnetic minerals and thus behave like weak magnets o The study of magnetic behavior has led to the realization that rocks preserve paleomagnetism a record of Earth s magnetic field Paleomagnetism provided


View Full Document

Access the best Study Guides, Lecture Notes and Practice Exams

Loading Unlocking...
Login

Join to view Geology Exam 2 Textbook and access 3M+ class-specific study document.

or
We will never post anything without your permission.
Don't have an account?
Sign Up

Join to view Geology Exam 2 Textbook and access 3M+ class-specific study document.

or

By creating an account you agree to our Privacy Policy and Terms Of Use

Already a member?