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Gli studenti saranno capaci di spiegare il concetto di deriva dei continenti e come la crosta terrestre si muova.

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Cosa ci dice la deriva dei continenti sulla geologia della Terra?

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Guardare un video introduttivo su YouTube sulla deriva dei continenti. Discutere i concetti chiave come presentati nel video.

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Costruzione di un modello semplice di deriva dei continenti utilizzando materiali facilmente reperibili. Questo aiuta a visualizzare come i continenti si sono mossi nel corso del tempo.

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Stampare una mappa in bianco delle dorsali medio-oceaniche. Ogni studente deve identificare e tracciare il movimento dei continenti.

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Creare in piccoli gruppi una mappa dettagliata della distribuzione delle placche tettoniche sulla base dei dati esistenti, utilizzando Padlet per collaborare e condividere risorse.

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Valutare la comprensione degli studenti attraverso osservazioni durante le attività di gruppo e discussioni guidate.

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Un quiz per testare la conoscenza acquisita sulla deriva dei continenti e il movimento della crosta terrestre.

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Discussione di gruppo per riassumere cosa hanno imparato gli studenti e le scoperte fatte durante la lezione.

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Ogni studente scrive brevemente cosa ha imparato oggi riguardo la deriva dei continenti e come questo cambia la percezione della Terra.

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Incarico di ricerca sulle evidenze attuali della deriva dei continenti e sulle teorie geologiche correlate.

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Completare un gioco online interattivo sui movimenti delle placche tettoniche.

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Play this game to explore how plates affect our planet. 1. Click on an orange marker to explore a place on the map. 2. Examine how tectonic plates are moving there. 3. Answer the question and read more about it!

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Leggere un articolo sulle recenti scoperte riguardanti le dorsali medio-oceaniche.

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This article was originally published for the International Commission on the History of Geological Sciences series of anniversary articles in the International Union of Geological Sciences (IUGS) E-bulletin in July 2022. This version has slight differences.
One can hardly do justice to Marie Tharp in an article of this length, as her life exemplifies so many strands of emerging science and disciplines as well as a sea-change in society as a whole. Her story points to the great value of the study of the history of disciplines, in the broad sense of geology as a whole, the emerging subsciences of geophysics and more sophisticated seismology, and as the newly coined oceanography. In a relatively short period, knowledge of the ocean floor went from an assumed almost featureless abyssal plain to a worldwide complex of ridges, valleys and transform faults showing regularly reversing strips of magnetism. Accounts of Marie Tharp's life also show a progression. She was at first nearly invisible, a "computer" as then known as she took numbers and translated them to maps. She was not allowed to go on ships to collect data, was basically ignored in published papers and was rarely referenced in histories, but her career ended with a full and fair assessment of her place in the complex story.

Her upbringing was unusual for her time. She was born in Ypsilanti, Michigan in 1920. When her mother had married at 40 to her 50-year-old husband, she retired from teaching German and Latin. Marie's father was a soil surveyor for the United States Department of Agriculture, mapping in the south in the winter and the north in the summer. The family moved constantly, and she had attended almost two dozen schools by the time she graduated from high school. Unsurprisingly, she was more a companion to her father and mother than to school friends. Her bond to her father increased when her mother died when she was fifteen. Her first choice of major at Ohio University was literature. She graduated in 1943 with a B.A. in English and music, along with 4 minors (Barton 2002: 216). Because most men were in the armed services, in 1943 the University of Michigan offered girls degrees in geology so they could work in the petroleum industry. Marie finished this master's degree in 1944 and took a job in Tulsa in an oil company office. She disliked both the office and the micropaleontology other girls were doing, so she went to Tulsa University and earned a B.S. in mathematics.

Here the story gets a bit more complex. Some biographies, and her own oral interviews mention only that, being bored in Tulsa, she went to New York City in 1948 and eventually found her job at the Lamont Laboratory of Columbia University. Her work at Columbia quickly became compelling. On the strength of her degree in mathematics she was sent to Dr. Maurice Ewing (1906-1974) who was puzzled about what she could do. When he inquired if she could draft, she told him she'd had a drafting job when at the University of Michigan, and so she was hired.

Bruce Heezen (1924-1977) arrived about two weeks later as one of Ewing's graduate students. At that time, the department was on the Columbia University campus, but soon accepted the donation of an estate that became the Lamont-Doherty Earth Observatory at Columbia University. Marie was soon working only with Heezen, drafting profiles of the ocean floor from data acquired from an echo sounder as a ship traversed the ocean. Heezen was very frequently at sea, collecting sonar lines across the north Atlantic which she translated into maps. These first maps showed a few individual tracks of the ships, filling in as more and more transits came into the records.

This was an exciting time in the new science of oceanography as the maps became part of a complex and worldwide story (as you may read about in the Voyages of the R/V Vema online exhibit). H. W. Menard (1920-1986), himself a geophysicist turned historian, wrote an excellent account of the surge of interest in all phases of the oceans in The Ocean of Truth: A Personal History of Global Tectonics, published in 1986. He recounted the story of the years of soundings via continuous echo recordings, seismicity, bathymetry, eventual magnetic surveys, and sea floor coring by many nations, all to increase during and after the Second World War with constantly improving instrumentation. The war was a catalyst for this interest and research, with the need to detect enemy submarines, protect the submarines and shipping of the Allies, and eventually to detect nuclear explosions. The profiles that Heezen had collected since 1947 were an essential part of it all (Barton 2002: 215). By 1952 Tharp and Heezen added physiographic shading to give a better impression of the actual shape of the deep ocean floor. They had thousands of depth measurements from the Lamont ships, but soon added tracks from other sources. Marie noted that "we had interminable rows of sounding numbers, numbers that I was supposed to turn into highly detailed and complete seafloor profiles" (Tharp,M., Connect the Dots, 1999). This was not easy, but Marie enjoyed her position, the work, and the company and the social life (drinks at five) that came with it. She continued:

Eventually, after the plotting, drawing, checking, correcting, redrawing and rechecking were done, I had a hodgepodge of disjointed and disconnected profiles of sections of 3 the North Atlantic floor. Plotted on a map, the ship's tracks looked like a spider's web, with the rays radiating out from Bermuda, where most of the research vessels took on supplies and water. Sometimes, the tracks zigzagged, as the ships fled from the paths of storms. (Tharp M. Connect the dots, 1999)

After six weeks more work, she had arranged the east to west tracks in order, north to south, and it was here that she saw that the only thing that lined up was a cleft in the middle of the ridges that had been revealed in the profiles. To Tharp it made sense that if material was forced up from below, the ridge would split apart. Heezen assumed there was an error, as he was an anti-drifter, or, like many of his time, saw no way for the sea floor to be expanding.

Better data kept coming in from the precision depth recorder (PDR) on Lamont's and others' ships. With an assistant for Tharp, it was all plotted to the same scale, 1:1,000,000. By then Heezen was working with Bell Laboratories in order to figure out why transatlantic cables were breaking. Heezen and Ewing had found turbidity currents in the deep ocean, activated by recorded earthquakes. Heezen engaged an assistant to map the earthquake epicenters, at the same scale as Tharp's mapping. At that point Heezen and Tharp noticed how closely the earthquakes followed the mid-ocean ridges. This had been previously noted, but Heezen saw that they actually fell in the rift valley. Plate tectonics on a world-wide basis was still in the future. Various explanations were proposed with various mechanisms: continental drift, sea floor expansion, subduction, were all conjectured. Ocean exploration was being carried out by multiple countries with different ships and instruments, in different oceans. Marie kept on mapping. Upwelling lava pushing the ridges apart made sense to her, but Heezen, Ewing, and many others were all opposed to expansion. Jacques Cousteau (1910-1997) did not believe the rift valley existed, and so towed a movie camera across it, thus proving its existence. It was at this point that one of the few early publications appeared that included Marie's name: the 1959 Geological Society of America's Special Paper 65, "The Floors of the Oceans," with authors Heezen, Tharp and Ewing.

By the mid 1960's the difficulties between Ewing and Heezen resulted in Heezen being banned from the Lamont ships. The positive result for Marie was that she was now able to accompany him on some voyages on other ships (for more on this topic, see Photos of the Month: The USNS Kane.) He continued with his position at Columbia. Marie's position disappeared, but because Heezen had multiple grants with the U.S. Navy and elsewhere, she continued her work from her home with similarly funded assistants. Although eventually they regained data from the Lamont ships, there were still many sources from U.S. ships and those from Russia, Germany, and elsewhere. Barton (2002) followed details of the changes in representation of their seafloor map making as it progressed from the north to the south Atlantic and on to the Indian and Pacific oceans and, eventually, all of the world's oceans. It incorporated not just ridges and valleys, but also the transform faults offsetting them. Color was added via the work of the Austrian painter, Heinrich Berann (1915-1999). The National Geographic Society facilitated printing successive colored maps, culminating in the famous topographic map of the world's ocean floors on a single sheet (Barton, 2002: 223). From this time onward, publications and recognition for Marie were much increased. She had always been happy to let others give the oral papers. Marie and Heezen shared sea time collecting data, as well as traveling the world for conferences. The final world map of the sea floor wasn't published until just after his death in 1977.

The debate about what was actually happening on the ocean floor continued, but the anti-drifters and anti-expansionists were finally convinced. Plate tectonics became a unified theory of earth behavior. Marie's work was fully recognized: in 1997 the Library of Congress named her one of the four great cartographers of the 20th century; in 1999 she received the Women Pioneer in Oceanography Award from the Woods Hole Oceanographic Institution; and in 2001 she was given the Lamont-Doherty Heritage Award. She facilitated getting Heezen's and her work into the Library of Congress. Lack of mention in some histories shows only the inattention of authors who omit this important part of a multifaceted story. To finish with Marie's comments:
Further Reading
Scientists and the general public got their first relatively realistic image of a vast part of the planet that they could never see. The maps received wide coverage and were widely circulated. They brought the theory of continental drift within the realm of rational speculation. I worked in the background for most of my career as a scientist, but I have absolutely no resentments. I thought I was lucky to have a job that was so interesting. Establishing the rift valley and the mid-ocean ridge that went all the way around the world for 40,000 miles---that was something important. You could only do that once. You can't find anything bigger than that, at least on this planet. (Tharp M. Connect the Dots, 1999).

Though I have by no means read all of the biographies and heard or read all of the multiple oral interviews about or with Marie, one thing that comes through is honesty about her work, and her place in the larger story. The overall trajectory of her career was increasing responsibility and recognition. The following list is a small sample of what is available, but attempts to be a fair representation of it. The best full and fair biography is that of Barton, 2002, in the Oldroyd volume.

Baker, V.R. 1999. Essay review: Naomi Oreskes; The Rejection of Continental Drift: Theory and Method in American Earth Science. Earth Sciences History 18:2, pp. 321-335.

Barton, C. 2002. Marie Tharp, oceanographic cartographer, and her contribution to the revolution in the Earth Sciences. Pp. 215-228, In Oldroyd, 2002.

Connect the Dots: See Tharp, in Lippsett Frankel, H. R. 2012. The Continental Drift Controversy. 4 V. Cambridge: Cambridge Univ. Press

Glen, W. 1982. The Road to Jaramillo. Stanford Univ. Press: Stanford, CA. ch.8.

Greene. M.T. 1999. Archival versus canned history. Earth Sciences History 18:2. Pp.336-343

Harrington, J.W. 1983. Dance of the Continents. Los Angeles: J.P.Tarcher, Inc.

Le Grand, H.E. 1988. Drifting Continents and Shifting Theories. New York: Cambridge Univ. Press.

Menard. H.W. 1986. The Ocean of Truth. Princeton N.J.: Princeton University Press.

Oldroyd, D.R. 1996. Thinking about the Earth: A History of Ideas in Geology. London: Athlone

Oldroyd, D.R. (Editor) 2002. The Earth Inside and Out: Some Major Contributions to Geology in the Twentieth Century. London: The Geological Society.

Oreskes, N. 1999. The Rejection of Continental Drift: Theory and Method in American Earth Science. New York: Oxford University Press.

Oreskes, N.1999. Living with uncertainty, learning from mistakes: Reply to Victor Baker and Mott Green. Earth Sciences History. 18:2, pp.344-350.

Oreskes, N. 2022. Operational oceanography. Pp. 102-109. American Scientist 110:2.

Sengor, A.M.C. 2018. Some notes on a history of ideas on rifts and extensional tectonics in general. Earth Sciences History 37:1, pp. 144-156.

Tharp, M. 1999. Chapter 2: Connect the Dots: Mapping the Seafloor and Discovering the MidOcean Ridge. IN Lippsett, L. (ed.) Lamont-Doherty Earth Observatory of Columbia, Twelve Perspectives on the First Fifty Years 1949-1999. Palisades N.Y.:L.-D. Earth Observatory of Columbia Univ.

Tharp, M. 1999a. Interview of Marie Tharp by Ronald Doel on 1994 September 14, Niels Bohr Library & Archives, American Institute of Physics, College Park, MD USA, www.aip.org/history-programs/niels-bohr-library/oral-histories/6940

More interviews with Marie Tharp at the American Institute of Physics may be found by searching for "Marie Tharp" here: https://www.aip.org/history-programs/niels-bohr-library/oral-histories.

Wood, R.M. 1985. The Dark Side of the Earth. London: George Allen & Unwin

The Lamont-Doherty website at http://marietharp.ldeacolumbia.edu/aboout-marie-tharp has a great deal of information as well as links to important literature.

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Marie Tharp's Discovery of the Mid Ocean Ridge Rift Valley in 1952

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One can hardly do justice to Marie Tharp in a paper of this length, as her life exemplifies so many strands of emerging science and disciplines as well as a sea-change in society as a whole.