Articles

1. The generation and evolution of the continental crust

   Hawkesworth, C J; Dhuime, B; Pietranik, A B; Cawood, P A; Kemp, A I S; Storey, C D
   Journal of the Geological Society, 03-01-2010

   Abstract: The continental crust is the archive of the geological history of the Earth. Only 7% of the crust is older than 2.5 Ga, and yet significantly more crust was generated before 2.5 Ga than subsequently. Zircons offer robust records of the magmatic and crust-forming events preserved in the continental crust. They yield marked peaks of ages of crystallization and of crust formation. The latter might reflect periods of high rates of crust generation, and as such be due to magmatism associated with deep-seated mantle plumes. Alternatively the peaks are artefacts of preservation, they mark the times of supercontinent formation, and magmas generated in some tectonic settings may be preferentially preserved. There is increasing evidence that depletion of the upper mantle was in response to early planetary differentiation events. Arguments in favour of large volumes of continental crust before the end of the Archaean, and the thickness of felsic and mafic crust, therefore rely on thermal models for the progressively cooling Earth. They are consistent with recent estimates that the rates of crust generation and destruction along modern subduction zones are strikingly similar. The implication is that the present volume of continental crust was established 2-3 Ga ago.

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2. Tectonic significance of present-day stress relief phenomena in formerly glaciated regions

   Christophe; Roberts, David; Gabrielsen, Roy H
   Journal of the Geological Society, 03-01-2010

   Abstract: Investigations were conducted in several regions of Norway with the purpose of detecting and measuring stress-relief features and to derive from them valuable information on the shallow-crustal stress state. Stress-relief features are induced by blasting and sudden rock unloading in road construction and quarrying operations, and are common in Norway and probably in other regions of Fennoscandia, as they are in NE America. Stress relief at the Earth's surface is diagnostic of anomalously high stress levels at shallow depths in the crust and characterizes the formerly glaciated Baltic and Canadian Precambrian shields. The mean orientation of the maximum horizontal compressive stress axis, as deduced from the orientation of stress-relief features, was found to be NW-SE, consistent with North Atlantic ridge-push forces. We show that our determined stress orientations are in excellent agreement with other kinds of stress data. As a final step, we estimate ridge-push force magnitudes from gravity data in the North Atlantic region. Our computations suggest that strong ridge-push forces characterize the Baltic and Canadian shields. We conclude from this quantitative analysis and our fieldwork results that present-day stress relief, in Fennoscandia and NE America, is mostly triggered by plate-scale ridge-push forces and not by residual glacial loading stresses.

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3. Integrative mapping of global-scale processes and patterns on "imaginary Earth" continental geometries: A teaching tool

   Sunderlin, David
   Journal of Geoscience Education, 01-01-2009

   ABSTRACT

   The complexity and interrelatedness of aspects of the geosciences is an important concept to convey in an undergraduate geoscience curriculum. A synthesis capstone project has served to integrate pattern-based learning of an introductory Earth History course into an active and process-based exercise in hypothesis production. In this exercise, students are given (1) an imaginary global continental configuration and (2) a general categorization of the global climate. Students then work through cause/effect relationships in Earth processes and hypothesize global biotic and abiotic patterns to be mapped upon the imaginary continental framework. Presentation and discussion of each student's imaginary earth and his/her interpretation of the various mappable parameters engages students in each other's reasoning and creative thought processes while promoting group learning and increasing science communication skills. Examination of the evidence and procedures used in the retrodiction of actual global paleogeographic scenarios is then placed in the context of this project. In practice, students have responded enthusiastically to the opportunity to develop geographic interpretations of an imaginary paleogeographic framework using their understanding of modern Earth systems. Upon exit evaluation, greater than 85% of the students taking part in the exercise felt more confident in their ability to hypothesize patterns from process.

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Historical Newspapers

1. CONTINENTAL DRIFT; PROFESSOR JOLY ON THE WEGENER THEORY

   The Irish Times. Dublin, Ireland: Jan 24, 1923. pg. 4

   Original Newspaper Image (PDF)

2. Continents Drifted Over South Pole, Geologists Believe

   The Washington Post. Washington, D.C.: Nov 16, 1937. pg. 6

   Original Newspaper Image (PDF)

3. CONTINENTS SEEN MOVING; Drifting Theory Is Gaining Some New Support

   The Sun. Baltimore, Md.: Sep 1, 1959. pg. 13, 1 pgs

   Abstract (Summary) The idea of footloose continents is gaining some support.

   Original Newspaper Image (PDF)

4. 'Plate Tectonics' The New Geology

   By EDMUND FULLER. Wall Street Journal. New York, N.Y.: Mar 11, 1975. pg. 20

   Abstract (Summary) "The ocean's bottom is at least as important as the moon's behind" ruefully witty but not flippant view of The American Miscellaneous Society, playfully serious name of a group of marine geophysicists, oceanographers, and other scientists in the Office of Naval Research, fighting for a fair share of funds available never enough unless there is a military angle somewhere.

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1. Teaching the content and context of science: The effect of using historical narratives to teach the nature of science and science content in an undergraduate introductory geology course

   by Vanderlinden, David Winston, Ph.D., Iowa State University, 2007 , 242 pages

   Abstract (Summary)
   This study reports the use of historically accurate narratives (short stories) to simultaneously teach geology content and the nature of science in an introductory, undergraduate geology course. The stories describe key events involved in the development of geologists' ideas about continental drift/plate tectonics and deep time/the age of the Earth. The design of the stories provides a highly contextualized setting which is designed to promote NOS and geology understanding by explicitly attending students to fundamental concepts and requiring students to reflect on the short story content. Evidence is reported to support the conclusion that students using these short stories constructed a better understanding of (1) the variety of processes involved in the construction of scientific knowledge, (2) the subjective nature of data that allows it to be interpreted differently by different scientists, and (3) the roles that culture and society play in determining the way in which scientific work is conducted and scientific ideas are constructed, while maintaining equal levels of understanding of geology content when compared to students who did not use the short stories. In some cases, students' preconceptions about objectivity in science, the degree to which scientific ideas can be considered as "proven" or "true," and the role of discovery in science appear to have adversely affected their ability to interpret the short story content in the ways intended. In addition, students' misconceptions about differences in how oceanic and continental plates were formed and geologists' use of relative and absolute dating techniques, especially the appropriate uses of radio-isotopic dating, are described.

   This study has implications for science instructors as they make efforts to efficiently use class time and curriculum resources to teach about the both the content and context of science and for geology instructors as they consider students' misconceptions about plate tectonics and deep time. In addition, this study presents a method for addressing concerns about many students' disinterest in science and the need to prepare a scientifically literate population.

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2. Global mantle convection models with mobile continents

   by Phillips, Benjamin R., Ph.D., Princeton University, 2005 , 104 pages

   Abstract (Summary)
   Continental motions are fundamental in shaping the Earth's surface. Features attributable to continental drift, such as orogenies and rifts, dominate subaerial geography. On an even grander scale, paleomagnetism suggests global continental reorganizations over time scales of hundreds of millions of years (Myr). In fact, supercontinental aggregations such as Pangea, Rodinia, and Columbia appear in the geologic record with a period of a few hundred Myr, suggestive of a cycle. These surface motions are likely coupled to mantle convection. Continents cluster over cold downwellings, as in the closing of the Tethys Ocean. Supercontinents apparently warm the mantle, as suggested by the African superplume, which lingers beneath the former site of Pangea. A number of geodynamic modelers have investigated the nature of this coupling, often generating results reminiscent of observations. Still, many such studies were limited by the use of Cartesian geometries that do not accurately represent the Earth. In this thesis I address the feedback between continents and the mantle using a high resolution, spherical, finite element (FEM) mantle convection code. I integrate a lithospheric model into the code, prescribing rigid, buoyant, mobile continents that serve as boundary conditions for the mantle. In a series of simulations with individual continents, I investigate the system's sensitivity to variations in fundamental mantle parameters and continent size. Continents covering 30%, 10%, and 3% of Earth's surface (representative of Pangea, Asia, and Antarctica, respectively) are introduced into mantle models characterized by pure core or radiogenic heating, and uniform or layered viscosity. Supercontinents are found effective in promoting the development of global thermal heterogeneities in an internally heated, layered viscosity mantle. Smaller continents behave passively and exhibit more time dependent behavior. Next, I introduce models incorporating three to six continents in layered viscosity models heated predominantly from within. These models reinforce the plausibility of a supercontinent cycle with a period of a few hundred Myr. Underlying mantle temperatures vary by up to 100 K over ?100 Myr. Continental velocities fluctuate in concert, ranging from ?0-7 cm/yr. These results agree well with geological and geophysical findings, and help constrain geodynamic models.

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3. A regional model to test the concept of global eastward mantle flow using finite elements

   by McColgan, Paul, Ph.D., The University of Oklahoma, 2009 , 149 pages

   Abstract (Summary)
   Computer modeling of tectonics involving the entire Caribbean and North Andes plates, as well as most of the Cocos plate and a portion of the Nazca plate, have been used to support the concept of a global eastward mantle flow beneath the region. The eastward flow is interpreted to be the results of a lithospheric rotation relative to the asthenosphere. The tectonic modeling has been used in combination with observations for the region to support a best fitting model that includes the global eastward flow.

   The best fitting model to surface observations used parameters consisting of a due east asthenosphere flow at 100 mm/yr, a base of lithosphere temperature of 1380 K, and a fault friction coefficient of 0.12. The results from the best model demonstrate that a simple uniform eastward flow in the asthenosphere can account for the varying directions of movement and velocities on the surface for the tectonic plates in this region. The model was able to reproduce the simultaneous movements for the Caribbean plate, at nearly due east, the North Andes plate to the northeast, the Nazca plate due east, and the Cocos plate to the northeast. In addition, the best model was able to reproduce the large velocity contrasts between the Cocos plate at 70 plus mm/yr relative to the Caribbean plate at 20 mm/yr and the velocity contrast between the Nazca plate at 50 plus mm/yr and the North Andes plate at 10 mm/yr. These results demonstrate that simple uniform flow of the asthenosphere to the east in conjunction with plate to plate interaction can explain the complex movements that we observe for the tectonics of this region, and might serve as an overall global model.

   For full-text documents see ProQuest's Dissertations & Theses Database