DBQ Sources: Earth’s Structure and Processes
BIGHISTORY PROJECT/ LESSON 2.6ACTIVITYDBQ SOURCES: EARTH’S STRUCTURE AND PROCESSESUnless otherwise noted, this work is licensed under CC BY 4.0. Credit: “DBQ Sources: Earth’s Structure and Processes,” OER Project, https://www.oerproject.com/1PurposeUse a variety of primary and secondary sources to deepen your understanding of how our knowledge of Earth’s structure and processes changed over time. ProcessAnalyze the following sources. If you’re using these sources to respond to an essay prompt, as you read, underlineor highlightany evidence that will support your claim. You can also use the HAPPY Toolor Quick Sourcing Tool. Document 1Source: Lyell, Charles. The Student’s Elements of Geology. London: John Murray, 1874.Sir Charles Lyell (1797–1875) was a Scottish geologist who argued that the Earth was shaped by gradual natural processes. These processes occurred over long time spans. In this excerpt, he described his theories, which he first proposed in the 1830s.Yet persistent as may be the leading features of land and sea on the globe, they are not unchanging . . . We also occasionally obtain evidence that submarine volcanoes are pouring out ash and streams of lava in mid-ocean as well as on land and that wherever mountains . . . are now the site of eruptions, there are signs of accompanying upheaval, by which beds of ashes full of recent marine shells have been uplifted many hundred feet. We need not be surprised, therefore, if we learn from geology that the continents and oceans were not always placed where they now are, although the imagination may well be overpowered when it tries to contemplate the quantity of time required for such changes.
BIGHISTORY PROJECT / LESSON 2.6ACTIVITYDBQ SOURCES: EARTH’S STRUCTURE AND PROCESSES2Document 2Source: Wegener, Alfred. The Origin of the Continents and Oceans. Translated by John Biram. New York: Dover Publications, Inc., 1966. Alfred Wegener (1880–1930) was a German meteorologist. He was one of the first people to make the hypothesis that continents are gradually moving, a process we call continental drift. The following is an excerpt from his 1915 book in which he explained his hypothesis.The concept of continental drift first came to me as far back as 1910, when considering the map of the world, under the direct impression produced by the congruence [similarity] of the coastline on either side of the Atlantic. At first, I did not pay attention to the idea because I regarded it as improbable. In 1911, I came quite accidentally upon a report in which I learned of paleontological evidence for a former land bridge between Brazil and Africa. As a result, I undertook a cursory examination of relevant research in the fields of geology and paleontology, and this provided immediately such weighty corroboration that a conviction of the fundamental soundness of the idea took root in my mind. The basic ‘obvious’ supposition [conjecture] that the relative position of the continents has never altered must be wrong. The continentsmust have shifted. South America must have lain alongside Africa and formed a unified block which was split in two; the two parts must then have become increasingly separated over a period of millions of years.
BIGHISTORY PROJECT / LESSON 2.6ACTIVITYDBQ SOURCES: EARTH’S STRUCTURE AND PROCESSES3Document 3Source: Below left:Heezen, Bruce and Marie Tharp. “Physiographic Diagram of the Atlantic Ocean.” Maps Collection, Regenstein Library: G9101.C2 1957 H.4. Below right: Heezen, Bruce C. and Marie Tharp.“World Ocean Floor.”Manuscript painting of the map by Heinrich C. Berann. Library of Congress Geography and Map Division, 1977.Marie Tharp (1920–2006) was an American geologist and oceanographic cartographer (mapmaker). In the late 1940s, Tharp started to analyze data gathered from ships crossing the Atlantic Ocean related tothe different depths of the ocean floor. She began converting this data into a map. In the 1950s, she collaborated with geologist Bruce Heezen to produce the first scientific map of the Atlantic Ocean floor. This research helped support a key discovery: the Mid-Atlantic Ridge. This provided evidence that supported the theories about continental driftand plate tectonics. Tharp faced an uphill climb to get her scientific work accepted, and her ideas were initially dismissed as “girl talk.”
BIGHISTORY PROJECT / LESSON 2.6ACTIVITYDBQ SOURCES: EARTH’S STRUCTURE AND PROCESSES4Document 4Source: Illustration created by Big History Project, 2014. Harry Hess(1906–1969)was a US Navy officer and Princeton geology professor who used sonar during World War II to map vast areas of the Pacific Ocean floor. In 1959,Hess wrote a paper explaining a process he called seafloor spreading. In this process, molten rock seeps up from the Earth’s interior through mid-ocean ridges (undersea mountain chains), spreads out to create new ocean floor, and then sinks back into the Earth’s interior through oceanic trenches. An illustration of this process is below.
BIGHISTORY PROJECT / LESSON 2.6ACTIVITYDBQ SOURCES: EARTH’S STRUCTURE AND PROCESSES5Document 5Source:Carey, S. Warren. Theories of the Earth and Universe: A History of Dogma in the Earth Sciences. Stanford, CA: Stanford University Press, 1988.Samuel Warren Carey (1911–2002) was an Australian geologist. He was one of the first people to support the idea of continental drift, and he continued to study plate tectonics for decades. He came up with a hypothesis, based on his plate tectonics research, that the Earth wasexpanding. In this excerpt, Carey described his controversial idea of the expanding Earth.I had realized in the mid-1930s that if Wegener was right, any mountain belts that were actively forming during the time of Wegener’s continental movement would be stretched or bent . . . in 1956 . . . I first realized that Wegener’s model was not possiblewithout expression of the earth. . . . I explained and illustrated the separation of continents by rift valleys progressively widening oceans by the repeated insertion of paired slices of mantle rock—the process that two decades later became the cornerstone of the ‘new global tectonics.’ . . . around 1976 . . . the global tectonic revolution in North America had defeated all opposition to the spread of continents . . . but . . . it still assumed . . . the patent [apparent] rapid growth of new oceanic crust, that the size of the earth had remained essentially constant. Hence it had to go back to the mechanism I had adopted in the 1930s and 1940s of swallowing great areas of crust down the ocean trenches, but which, after 20 years of working with it, I had found by 1956 to be unworkable on a global scale. Hence . . . I had concluded that not only had the volume of the earth greatly increased, but so had its mass.