Chapter 10: Plate Tectonics

Section 1: Continental Drift http://education.sdsc.edu/optiputer/flash/pangea_4.htm

Theory of Continental Drift A Dutch cartographer, Ortelius, noted the fit of the coastlines of Africa and S. America. In 1912, Alfred Wegener thought that the shape of the continents was no coincidence. He proposed his idea of continental drift to scientists, but couldn’t tell them why they formed puzzle-like pieces. He proposed that perhaps the continents were plowing through the ocean floor, and the movement was caused by Earth’s spinning on its axis. He called the land mass of all lands “Pangaea.” It was a very controversial idea at the time.

A Variety of Animations http://www.nature.nps.gov/geology/usgsnps/animate/pltecan.html

India Slamming into the Eurasian Continent http://education.sdsc.edu/optiputer/flash/indiaMove.htm

Evidence The continents fit together like puzzle pieces. If you look at the continental shelves of continents, they fit even better.

Evidence 2. Fossil clues Like fossils were found along continental boundaries, supporting that they had once been together.

Evidence—Fossils (continued) The fossil of the Glossopteris plant was found on many continents, even Antarctica, which gives evidence that Antarctica had once been at a warmer latitude than it is now. The Mesosaurus reptile fossil was found in S. America and Africa, supporting the theory that these two continents were once connected. The Mesosaurus was likely a fresh-water reptile. It did not have the capability to swim long distances.

MESOSAURUS

GLOSSOPTERIS Fossil of extinct Glossopteris tree Glossopteris as it looked on Pangaea

Evidence 3. Climate evidence on various continents. Glacial scratches and deposits matched across continents. Evidence of past glaciers is found in tropical areas where no glaciers could be. Fossils of warm-weather plants were found in Arctic and Antarctic regions.

CLIMATE CLUES: Glacial Features

Evidence 4. Matching rocks and mountain ranges. Rocks types match up on different continents, supporting that continents were together. Mountain ranges such as the Appalachian Mountains of the eastern U.S. are similar to those found in Greenland and western Europe. S. American rocks on the eastern side match up with rocks on the western edge of Africa. Evidence

Matching Mountain Ranges

How could continents drift? After Wegener’s death, more clues were found. Modern technology helped with this. Google Earth Sea floor spreading supports the idea, as well.

Quick Review Wegener’s theory of Continental Drift is supported today by four main parts: The observation that the continents fit together like puzzle pieces. The fossils Glossopteris and Mesosaurus are two fossils that are found on different continents. Climate clues like glacier tracks and fossils of plants in Arctic regions support that continents have moved. Rocks and mountain ranges on different continents match.

Section 2: Seafloor Spreading

Mapping the Ocean Floor Before WWI, the seafloor was mapped by sailors lowering a rope with a weight until it hit bottom. The rope was raised and measured, and this was repeated.

Mapping the Ocean Floor During WWI, sound waves were used to detect submarines. This technology was then transferred to mapping the ocean floor This is called SONAR Stands for “SOund NAvigation and Ranging”

Support for Wegener, at Last! In the early 1960s, American scientist Harry Hess looked at evidence from SONAR and suggested that the seafloor is spreading. He said that hot, less dense material below Earth’s crust rises to the surface at the mid-ocean ridges, leaks out, cools and causes the seafloor to spread in both directions.

How Seafloor Spreading Happens http://www.wwnorton.com/college/geo/egeo/animations/ch2.htm#3 http://www.wwnorton.com/college/geo/egeo/flash/2_5.swf

More on Seafloor Spreading

Clues on the Sea Floor In 1968, the research ship Glomar Challenger gathered rock samples and determined that the youngest rock was near the mid ocean ridges and got older farther away from the ridges. Magnetism in these rocks also showed that the north and south poles switch places over time. http://www.indiana.edu/~g103/plate/magstrip.swf http://www.youtube.com/watch?v=GyMLlLxbfa4&feature=results_video&playnext=1&list=PL8319D7A4F1ACA3CE

The Glomar Challenger

Magnetic Time Scale Iron particles in magma align to the poles when it leaks out. When the magma cools, the particles are locked in place, leaving a record of pole reversals on the ocean floor. As new magma leaks out, it pushes the old magma to the side. When the poles switch, the particles do, too.

Magnetic Reversals http://earthguide.ucsd.edu/eoc/teachers/t_tectonics/p_paleomag.html

Recorded on the Ocean Floor

Hydrothermal Vents http://www.divediscover.whoi.edu/vents/video.html http://videos.howstuffworks.com/science-channel/29268-100-greatest-discoveries-sea-floor-spreading-video.htm http://www.youtube.com/watch?v=f9o5BV1aotM&feature=fvsr

Earth’s Magnetic Field

Protecting Earth

Section 3: Theory of Plate Tectonics Plate tectonics is a theory that explains how Earth’s crust and part of the upper mantle are broken into sections that move. These sections are called plates.

Earth’s Layers

What’s Earth Made Of? http://education.sdsc.edu/optiputer/flash/insideEarth.htm http://education.sdsc.edu/optiputer/flash/outerLayers.htm http://education.sdsc.edu/optiputer/flash/generalLayers.htm

What Are Earth’s Plates Made Of? The crust and part of the upper mantle make up the lithosphere. These, together float as plates—or broken sections of lithosphere—upon the flexible layer called the asthenosphere.

Plate Boundaries Where plates meet and interact are plate boundaries. Divergent boundaries Convergent boundaries Transform boundaries

Divergent Boundaries

Major Plate Boundaries http://education.sdsc.edu/optiputer/flash/plates2.htm http://education.sdsc.edu/optiputer/flash/plates3.htm

Different Types of Boundaries http://education.sdsc.edu/optiputer/teachers/platemovement.html

Convection in the Earth http://www.classzone.com/books/earth_science/terc/content/visualizations/es0805/es0805page01.cfm?chapter_no=visualization

How Fast Do the Plates Move?