Continental Drift and Seafloor Spreading Notes PDF

Continental Drift  Early Observations In 1912, German meteorologist Alfred Wegener presented his ideas about continental movement to the scientific community. Wegener developed a hypothesis that he called continental drift, which proposed that Earth’s continents had once been joined in a s...

Continental Drift  Early Observations In 1912, German meteorologist Alfred Wegener presented his ideas about continental movement to the scientific community. Wegener developed a hypothesis that he called continental drift, which proposed that Earth’s continents had once been joined in a single landmass, called Pangea, that broke apart about 200 MYA and sent the continents adrift.  Evidence of Continental Drift 1 2 3 4 Rock Formations Fossils Climate Glaciers Rocks in the Similar fossils of The existence of coal Glacial deposits Appalachian animals and beds in Antarctica to nearly 300 million Mountains in the US plants that once conclude that years old on several were identical to lived on or near Antarctica must continents led layers of rocks in land had been have been much Wegener to propose similar mountains in found on widely closer to the that these land Greenland and separated equator sometime masses might have Europe. continents. in the geologic past. once been joined and covered with ice. Seafloor Spreading Mapping the Ocean Floor One technological advance that was used to study the ocean floor was the magnetometer, a device that can detect small changes in magnetic fields. Towed behind a ship, it can record the magnetic field generated by ocean floor rocks. Developments in sonar technology enabled scientists to measure water depth and map the topography of the ocean floor.  Using the maps made from data collected by sonar and magnetometers, scientists discovered that vast, underwater mountain chains called ocean ridges run along the ocean floors around Earth. Deep-sea trenches run alongside ocean ridges and form when one tectonic plate goes under another.  Ocean Rocks and Sediments Scientists collected samples of deep-sea sediments and the underlying oceanic crust. 01 02 03 The ages of the rocks The oldest parts of the ocean-floor crust is that make up the seafloor are thinner than seafloor vary across geologically young. continental (land) the ocean floor. The This is much younger crust. age of oceanic crust than continental INCREASES with rocks, which can be distance from a ridge. billions of years old. Ocean Rocks and Sediments Observations of ocean-floor sediments revealed that, like the age of ocean crust, the thickness of ocean-floor sediments INCREASES with distance from an ocean ridge. Seafloor Spreading Seafloor spreading is the theory that explains how new oceanic crust is formed at ocean ridges, slowly moved away from ocean ridges, and destroyed at deep-sea trenches. During seafloor spreading, magma, which is hotter and less dense than surrounding mantle material, is forced toward the surface of the crust along an ocean ridge. As spreading along an ocean ridge continues, more magma is forced upward and solidifies. Seafloor Spreading Seafloor spreading provided the explanation that Wegener lacked. Continents do not push through ocean crust, as he proposed. Instead, they are like passengers that ride along while ocean crust slowly moves away from ocean ridges.