Module #10 - Plate Tectonics, History and Evidence

INSTRUCTIONS FOR TODAY

1. Watch the following video: Video of the Day:  The Theory of Plate Tectonics (flipped classroom lecture) (9 minutes)

Be sure to make point form notes in your digital video journal. Please make sure this document is SHARED with Mr. Durk.

2. Read the following information below in Part 1: Background and Terminology. Follow all hyper-links to external websites for activities, demonstrations and videos (if applicable). Copy only KEY information (i.e. the highlighted terms) to your  notebook. You may work with a partner to do this as there are quite a few key terms and concepts to get down.

3. Part 2: Plate Boundaries - Case Study / Activity

4. Complete Part 3: Quiz - using UGDSB LMS  (see below) and complete in class between 11:15 - 11:45 am.

5. If time or for HOMEWORK: Watch the Video: Colliding Continents and make point form notes in your video journal. NOTE: Your Video Journal will be assessed by this Friday April 15th in time for Mid Term Reports.

DUE DATE for Part 2:  Before Module #11 (Wed. April 13th)

Part 1: Background and Terminology

Record IconPlease remember to record all definitions and content in your virtual notebook for your own use. Definitions can be found by clicking on highlighted words.

History

The theory of plate tectonics states that the earth's outermost layer is fragmented into a dozen or more large and small plates that are moving relative to one another as they ride atop hotter, more mobile material. Plate tectonics is a relatively new scientific concept, introduced some 30 years ago, but it has revolutionized our understanding of the dynamic planet upon which we live. The theory has unified the study of the earth by drawing together many branches of the earth sciences, from paleontology (the study of fossils) to seismology(the study of earthquakes). It has provided explanations to questions that scientists had speculated upon for centuries, such as why earthquakes and volcanic eruptions occur in very specific areas around the world, and how and why great mountain ranges like the Alps and Himalayas formed.

Before the advent of plate tectonics, however, some people already believed that the present-day continents were the fragmented pieces of pre-existing larger landmasses ("supercontinents"). Even though this belief that continents have not always been fixed in their present positions was suspected long before the 20th century, it wasn’t until then that any scientific advances were made to formulate the theory of plate tectonics . Three major contributors helped advance the notion of plate tectonics during the 20th century: Alfred Wegener, Harry Hess, and Tuzo Wilson.

Alfred Wegener, developer of the Continental Drift Theory

Alfred Lothar Wegener: Continental Drift

In 1912, a 32-year-old German meteorologist named Alfred Lothar Wegener published two articles on his scientific theory called Continental Drift, the forerunner to the theory of plate tectonics. He contended that, around 200 million years ago, the supercontinent Pangaea began to split apart into the various smaller continents that exist today.

Wegener's theory was based in part on what appeared to him to be the remarkable fit of the South American and African continents, first noted by Abraham Ortelius three centuries earlier. Wegener was also intrigued by the occurrences of unusual geologic structures and of plant and animal fossils found on the matching coastlines of South America and Africa, now widely separated by the Atlantic Ocean. He reasoned that it was physically impossible for most of these organisms to have swum or been transported across the vast oceans. To him, the presence of identical fossil species along the coastal parts of Africa and South America was the most compelling evidence that the two continents were once joined.

According to the continental drift theory, the supercontinent Pangaea began to break up about 225-200 million years ago, eventually fragmenting into the continents as we know them today.
 
Acknowledgements: The Canadian Encylopediat

In Wegener's mind, the drifting of continents after the break-up of Pangaea explained not only the matching fossil occurrences but also the evidence of dramatic climate changes on some continents. For example, the discovery of fossils of tropical plants in the form of coal deposits in Antarctica led to the conclusion that this frozen land previously must have been situated closer to the equator, in a more temperate climate where lush, swampy vegetation could grow. Other mismatches of geology and climate included distinctive fossil ferns (glossopteris) discovered in now-polar regions, and the occurrence of glacial deposits in present-day arid Africa, such as in the Vaal River valley of South Africa.

Harry Hammond Hess: Spreading the Sea Floor

Harry Hess (1906-1969) in his Navy uniform as captain of the assault transport Cape Johnson during World War II. After the war, he remained active in the Naval Reserve, reaching the rank of Rear Admiral.Harry Hammond Hess, a professor of geology at Princeton University, was very influential in setting the stage for the emerging plate tectonics theory in the early 1960s. He believed in many of the observations Wegener had used in defending his theory of continental drift, but he had very different views about large-scale movements of the earth.

While serving in the U.S. Navy during World War II, Hess, with the cooperation of his crew, was able to conduct echo-sounding surveys in the Pacific while cruising from one battle to the next. His research ultimately resulted in a ground-breaking hypothesis that later would be called sea floor spreading. In 1959, he informally presented this hypothesis in a manuscript that was widely circulated. Hess, like Wegener, ran into resistance because little ocean floor data existed to test his ideas. In 1962, his ideas were published in a paper titled "History of Ocean Basins," one of the most important contributions to the development of plate tectonics. In this classic paper, Hess outlined the basics of how sea floor spreading works: molten rock (magma) oozes up from the earth's interior along the mid-oceanic ridges, creating new sea floor that spreads away from the active ridge crest and, eventually, sinks into the deep oceanic trenches.

Hess' concept of a mobile sea floor explained several very puzzling geologic questions. If the oceans have existed for at least four billion years, as most geologists believed, why is there so little sediment deposited on the ocean floor? Hess reasoned that the sediment has been accumulating for about 300 million years at most. This interval is approximately the time needed for the ocean floor to move from the ridge crest to the trenches, where oceanic crust descends into the trench and is destroyed. Meanwhile, magma is continually rising along the mid-oceanic ridges, where the "recycling" process is completed by the creation of new oceanic crust. This recycling of the sea floor also explained why the oldest fossils found on the sea floor are no more than about 180 million years old. In contrast, marine fossils in rock strata on land can be considerably older. Most importantly, however, Hess' ideas also resolved a question that had plagued Wegener's theory of continental drift: how do the continents move? With sea floor spreading, the continents would not have to push through the ocean floor but would have been carried along as the ocean floor spread from the ridges.

In 1962, Hess was well aware that solid evidence was still lacking to test his hypothesis and to convince a more receptive but still skeptical scientific community. But the Vine-Matthews explanation of magnetic striping of the sea floor a year later and additional oceanic exploration during subsequent years ultimately provided the arguments to confirm Hess' model of sea floor spreading. The theory was strengthened further when dating studies showed that the sea floor becomes older with increased distance away from the ridge crests. Finally, improved seismic data confirmed that oceanic crust was indeed sinking into the trenches, fully proving Hess' hypothesis, which was based largely on intuitive geologic reasoning. His basic idea of sea floor spreading along mid-oceanic ridges has well withstood the test of time.A theoretical model of the formation of magnetic striping. New oceanic crust forming continuously at the crest of the mid-ocean ridge cools and becomes increasingly older as it moves away from the ridge crest with sea floor spreading (see text): a. the spreading ridge about five million years ago; b. about two to three million years ago; and c. in the present day.
 
Acknowledgement: Image provided by USGS

J. Tuzo Wilson: Discovering Transforms and Hot spots

Canadian geophysicist J. Tuzo Wilson was also pivotal in advancing the plate tectonics theory. Intrigued by Wegener's notion of a mobile Earth and influenced by Harry Hess' exciting ideas, Wilson was eager to convert others to the revolution brewing in the earth sciences in the early 1960s. Wilson had known Hess in the late 1930s, when he was studying for his doctorate at Princeton University, where Hess was a dynamic young lecturer.

In 1963, Wilson developed a concept crucial to the plate tectonics theory. He suggested that the Hawaiian and other volcanic island chains may have formed due to the movement of a plate over a stationary "hot spot" in the mantle. This hypothesis eliminated an apparent contradiction to the plate tectonics theory - the occurrence of active volcanoes located many thousands of kilometres from the nearest plate boundary. Although hundreds of subsequent studies have proven Wilson correct, in the early 1960s, his idea was considered so radical that his "hot spot" manuscript was rejected by all the major international scientific journals. This manuscript ultimately was published in 1963 in a relatively obscure publication, the Canadian Journal of Physics, and became a milestone in plate tectonics.

J. Tuzo Wilson (1908-1993) made major contributions to the development of the plate tectonics theory in the 1960s and 70s. He remained a dominant force in the Canadian scientific scene until his death.
 

Artist's conception of the movement of the Pacific Plate over the fixed Hawaiian "hot spot," illustrating the formation of the Hawaiian Ridge-Emperor Seamount Chain. (Modified from a drawing provided by Maurice Krafft, Centre de Volcanologie, France).Another of Wilson's important contributions to the development of the plate tectonics theory was published two years later. He proposed that there must be a third type of plate boundary to connect the oceanic ridges and trenches, which he noted can end abruptly and "transform" into major faults that slip horizontally. A well-known example of such a transform fault boundary is the San Andreas Fault zone. Unlike ridges and trenches, transform faults offset the crust horizontally, without creating or destroying crust.

J. Tuzo Wilson's original diagram (slightly modified), published in 1963, to show his proposed origin of the Hawaiian Islands.Like Hess, Wilson was able to see his concepts of hot spots and transform faults confirmed, as knowledge of the dynamics and seismicity of the ocean floor increased dramatically. Wilson and other scientists, including Robert Dietz, Harry Hess, Drummond Matthews, and Frederick Vine, were the principal architects in the early development of plate tectonics during the mid-1960s, a theory that is as vibrant and exciting today as it was when it first began to evolve less than 50 years ago. Interestingly, Wilson was in his mid-fifties, at the peak of his scientific career, when he made his insightful contributions to the plate-tectonics theory. If Alfred Wegener had not died at age 50 in his scientific prime, the plate tectonics revolution might have begun sooner. 
Acknowledgement: Images provided by USGS

external linkResources

  1. Plate Tectonics, The Canadian Encyclopedia
  2. This Dynamic Earth, USGS
  3. J. Tuzo Wilson, Canadian Mining Hall of Fame

As noted by Snider-Pellegrini and Wegener, the locations of certain fossil plants and animals on widely separated present-day continents would form definite patterns (shown by the bands of colors), if the continents were rejoined.

 

 
Acknowledgements: Content provided by USGS

external linkResources

  1. Plate Tectonics, The Canadian Encyclopedia
  2. This Dynamic Earth, USGS
  3. J. Tuzo Wilson, Canadian Mining Hall of Fame

Part 2: Case Study: Plate Boundaries

Drop Box Go to this LINK.  Follow these instructions for your Case Study:

1. Choose one specific plate boundary (see list provided)  (i.e. San Andreas Fault - California, USA) and complete the following:

a. Describe the motions of the plates involved at this boundary. Include the direction of movement of the plates and the rate at which they are moving. Describe the type of plates involved: continental-continental, continental-oceanic or oceanic-oceanic, etc.

b. Describe some of the Natural hazards / Disasters (earthquakes, volcanoes, tsunami) that have occurred in recent history at this boundary. Include information on the geology of the event, the number of people killed, damage and any other relevant of interesting information. Provide links to useful videos and / or images to supplement your summary.

c. Provide 2-3 useful websites / links (reliable sources) that provide useful and relevant information about this plate boundary.

Be sure to LINK your google doc to the CHART for all in the class to view.

Part 3: Quiz: Geology & Plate Tectonics (20 marks)

Drop BoxLog onto the UGDSB D2L site and complete Quiz #3

NOTE: You must complete the quiz between 11:00 - 11:45 am today only. ONLY the TAB for the D2L should be open on your chromebook.

GOOD LUCK!