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Plate Tectonics
Plate tectonics explains the causes of earthquakes and other geological phenomena. According to "National Geographic," these plates cover the lithosphere, an area that includes the Earth's crust and mantle. As the plates move, they create three types of tectonic boundaries, which are known as convergent, divergent and transform boundaries. With convergent boundaries, tectonic plates collide and crumple to form mountains or undersea trenches, such as the Mariana Trench. Divergent boundaries move away from each other and are responsible for landforms like the Great Rift Valley of Africa. Additionally, divergent boundaries cause continents to slowly move across the globe over millions of years. Transform boundaries differ from their counterparts, because they do not create landforms. Instead, two plates "rind past each other and cause earthquakes, such as San Fransisco's major earthquake of 1906.
Theory
Although plate tectonics is well understood, the actual root cause eludes geologists. Vicki Hansen of the University of Minnesota proposes an unusual, yet conceivable, theory. Hansen suggests a meteor impact 3 billion years ago created a chain reaction that led to the plate tectonics seen today. Early Earth was once universally covered by a soft layer called the felsic crust, which rested above the dense, molten mantle underneath. According to Hansen's theory, a massive meteor strike to a weak spot in the felsic crust caused the mantle to erupt. In turn, lava spewed to the surface and solidified to create the mafic crust. The brittle mafic crust spread until it was forced under the softer felsic crust. Finally, this fragmentation and rearrangement of the Earth's surface triggered plate tectonics.
Meteor Activity
What lends veracity to Hansen's theory is that Earth was a very different place 3 billion years ago. Unlike today, the solar system was once laden with massive asteroids and pieces of "failed planets" that had not formed successfully. Meanwhile, Earth and its surrounding planets were regularly bombarded with meteors of all sizes. Any one of these impacts could have triggered plate tectonics.
Implications
If correct, Hansen's theory not only explains the catalyst behind Earth's many landforms and earthquakes, but it essentially reveals how plate tectonics began on any planet. While plate tectonics is a major geological area of study, meteor impacts receive comparatively little attention beyond certain mass extinction events. This hypothesis is a significant step in unraveling Earth's geological history.