Development of the Plate Tectonics Theory
Make observations about the following maps: (Click on each map for a larger view.)
(Copyright of all these materials remains with Dale S. Sawyer http://plateboundary.rice.edu/)
Refer to the following map for names of locations:
Volcanology (Volcanoes)
Seafloor Age
Topography/Bathymetry
Fossil Evidence
1858: Geologist Eduard Seuss points out that fossils of the Glossopteris plant are found in southern Africa, South America, Australia, Antarctica, and India.
Glossopteris: an extinct group of seed plants that arose during the Permian on the great southern continent of Gondwana. These plants went on to become a dominant part of the southern flora through the rest of the Permian, though they dwindled to extinction by the end of the Triassic Period.
Lystrosaurus: Lystrosaurus was part of a reptile and mammal-like group of animals known as the Synapsidas. These animals were neither a reptile nor a mammal, but were probably an intermediate group, as reptiles evolved into modern day mammals. Lystrosaurus, a pig-sized animal, used its beak-like mouth to eat plants. Because Lystrosaurus did not have any teeth, it is believed that it probably mashed up the plants it ate in its guts. Lystrosaurus was a very successful animal, spreading throughout the world.
Mesosaurus: a small reptile that swam in shallow coastal waters about 275 million years ago. It couldn't have crossed an ocean, yet Mesosaurus fossils are found in both South America and Africa.
Cynognathus: an early relative of mammals. It lived about 235-250 million years ago.
Distribution of Rocks and Mountain Belts
1927: Geologist Alexander du Toit observes rock layers on the western coast of Africa in the following sequence: basalt rock, shale contain ing fossil reptiles, coal layers containing Glossopteris fossils, rocks containing Mesosaurus fossils, and shale. He discovers an almost identical sequence of rock layers on the eastern coast of South America.
View the following FLASH Interactive: https://gln.dcccd.edu/Geology_Demo/content/Lesson1/GEO01-13b.swf
Glacial Deposits
Climate changes over time:
Earth Over Time...
Theory of Continental Drift Interactive http://www.exploratorium.edu/origins/antarctica/ideas/gondwana2.html
1944: Geologist Bailey Willis calls Wegener’s theory a fairy tale. He says it seems impossible that the continents could move.
What was Wegener missing? (How the plates were moving...)
Convection Currents!
http://www.antonine-education.co.uk/Pages/Physics_GCSE/Unit_1/Core_03_Transfer/Core_03.htm
http://earth.usc.edu/classes/geol150/stott/variability/images/tectonics/mantleconvection.jpg
1960's Hess provides evidence to support Wegener's Theory, leading to The Theory of Plate Tectonics.
Find out about Harry Hess...
What was the name of Hess's theory?
Image found at http://www.gcsescience.com/pwav67.htm
http://www.pbs.org/wgbh/aso/tryit/tectonics/divergent.html
Hess's problem: Why isn't Earth expanding?
1963: John Tuzo Wilson
Hot Spots: This hypothesis eliminated an apparent contradiction to the plate-tectonics theory -- the occurrence of active volcanoes located many thousands of kilometers from the nearest plate boundary.
http://pubs.usgs.gov/gip/dynamic/graphics/Pacific_basin.gif
1965: Wilson suggested a third type of plate boundary which offset crust sideways without creating or destroying crust.
1980s: Satellites and lasers are used to measure the movement of continents. They continue to move at an average of about 2 cm (0.8 in) per year
Tracking Plate Motion from Space (https://cimss.ssec.wisc.edu/sage/geology/lesson2/concepts.html)
Today we can track the current direction and speed of plate motion with ground surveying techniques using laser-electronic instruments and by space-based methods such as with satellite networks. Since plate motions are at a global scale, they are best measured by satellite-based methods. The three most commonly used space-based techniques are: very long baseline interferometry (VLBI), satellite laser ranging (SLR), and the Global Positioning System (GPS). Among these three techniques, GPS has been the most useful for studying plate motions to date.
The GPS satellite network includes twenty-four satellites that are currently in orbit 20,000 km above the Earth as part of the NavStar system of the U.S. Department of Defense. These satellites continuously transmit radio signals back to Earth. To determine a precise position on Earth (longitude, latitude, elevation) triangulation is used. From any one position on earth one must simultaneously receive signals from at least four satellites, recording the exact time and location of each satellite when its signal was received. By repeatedly measuring distances between specific points, geologists can determine if there has been active movement between plates.
Plate motion can be measure as relative movement or absolute movement. Absolute plate movement is the motion of a plate with respect to the Earth’s deep interior (Figure 14). Relative movement refers to the movement between two plates at a given point on the plate boundary. For every pair of plates their relative motion is defined by a direction and a magnitude. This movement has a magnitude of typically tens of mm per year (Figure 15). It is relative plate movement that determines the amount and type of earthquake and volcanic activity present along a plate boundary.
Global map of current absolute plate motion as calculated using GPS technology and the Jules Verne Voyager: Earth software. The direction of arrows indicated the direction of plate movement. The length of the arrow indicates the speed of movement (note relative arrow length of the key in the upper left corner). (From Jules Verne Voyager: Earth)