Plate Tectonics PDF

Plate Tectonics Have you ever wondered how mountains form? What about forces of nature such as volcanoes or earthquakes? The answers to these questions are found in the layers of Earth and the concept of plate tectonics! The cr...

Plate Tectonics Have you ever wondered how mountains form? What about forces of nature such as volcanoes or earthquakes? The answers to these questions are found in the layers of Earth and the concept of plate tectonics! The crust is the top layer of Earth’s surface, and the core is the center layer. A thick layer of molten rock can be found between the crust and core. This layer of molten rock is known as the mantle. The lithosphere is made up of Earth’s crust and the uppermost part of the mantle. Cool and rigid, the lithosphere is the outermost layer of lithosphere – consists of the crust Earth and is broken into large, thick pieces called (light brown) and upper mantle tectonic plates. These tectonic plates contain different (dark brown) kinds of crust, oceanic and continental. Both are less molten – melted; liquefied dense than the mantle, but oceanic crust is denser than continental crust. This is one reason why continents are tectonic plates – the broken pieces higher than the ocean floor. However, some continental of the lithosphere that move on the plates are submerged in the ocean, and some oceanic asthenosphere plates, such as the entirety of Iceland, are above the ocean. Scientists have given names to Earth’s tectonic plates. This map shows the current major tectonic plates. Many of these plates are named for the continents or oceans they support. Maps of ancient land and water patterns show how Earth’s plates have moved great distances, collided, and spread apart. Earth’s major tectonic plates include the African Plate, Antarctic Plate, Eurasian Plate, Indian Plate, Australian Plate, North American Plate, South American Plate, and Pacific Plate. 1  Plate Tectonics How did scientists discover that the tectonic plates moved? Was that movement related to geological structures such as mountains or valleys? Was it related to earthquakes or volcanoes? Look at the world map and notice the shapes of the continents. Do you see how some continents appear to fit together like the pieces of a jigsaw puzzle? Why do you think this is? Is it just a coincidence, or do you think it suggests something important about the history of our planet? Continental Drift If you noticed the continents appear to fit together like a jigsaw puzzle, you are not alone. In the early 20th century, a German scientist named Alfred Wegener noticed this phenomenon. Wegener hypothesized that at one or more points in Earth’s history, the continents were connected. Wegener looked for further evidence that the continents may have been connected and moved over time. Evidence of Continental Movement Wegener noticed evidence of matching geologic structures. He looked for connections between the matching coastlines. Where coastlines appeared to fit together, Wegener noticed that certain geologic formations also appeared to fit together. For example, a mountain range on one coastline appeared to connect with a mountain chain on the opposite coastline. Several deposits of sediments left behind by glaciers also lined up along the matching coastlines of continents. 2  Plate Tectonics In addition to geologic evidence, Wegener found matching fossil evidence that supported his theory that the continents may once have been connected. Fossils of a freshwater reptile called Mesosaurus were found on both the eastern coast of South America and the western coast of South Africa. It is highly unlikely these freshwater animals swam across the entire Atlantic Ocean while they were alive. Fossils of a land reptile called Lystrosaurus were also found along matching coasts of eastern Africa, central India, and Antarctica. These land animals also could not have crossed the oceans separating these continents. Equally unlikely is the possibility that the same species evolved independently on multiple continents. Instead, Wegener reasoned the continents must have been joined at one time. As the continents moved apart, they took Mesosaurus and Lystrosaurus fossils with them. 3  Plate Tectonics Wegener concluded from his findings that the continents must have moved over time. Scientists gave the process its more familiar name, continental drift. At least once in Earth’s history, the continents were connected in large landmasses, or supercontinents. Around 250 million years ago, all the continents were connected in one giant supercontinent. Wegener named this supercontinent Pangaea, which means “all the Earth.” Over millions of years, the continents moved apart to their present-day positions. Despite the evidence Wegener collected, he could not provide a theory explaining how the continents moved over time. Partly for this reason, his hypothesis was initially rejected by the scientific community. Then, in the 1940s, scientists discovered new evidence about seafloor spreading that suggested how continents drift. Wegener on an Unfortunately, Wegener did not live to see his work validated. He expedition in Greenland, froze to death on an expedition across the Greenland ice cap, trying to prove his trying to prove his hypothesis. hypothesis. 4