{"id":1864,"date":"2016-05-23T20:46:21","date_gmt":"2016-05-23T20:46:21","guid":{"rendered":"https:\/\/courses.lumenlearning.com\/geologyxwaymakerxmaster\/?post_type=chapter&p=1864"},"modified":"2025-10-13T16:49:20","modified_gmt":"2025-10-13T16:49:20","slug":"reading-theory-of-plate-tectonics-2","status":"publish","type":"chapter","link":"https:\/\/courses.lumenlearning.com\/geo\/chapter\/reading-theory-of-plate-tectonics-2\/","title":{"raw":"Reading: Theory of Plate Tectonics","rendered":"Reading: Theory of Plate Tectonics"},"content":{"raw":"

When the concept of seafloor spreading came along, scientists recognized that it was the mechanism to explain how continents could move around Earth\u2019s surface. Like the scientists before us, we will now merge the ideas of continental drift and seafloor spreading into the theory of plate tectonics.<\/p>\r\n

Learn more about continental drift and the mechanism of seafloor spreading create plate tectonics<\/a>.<\/p>\r\n\r\n

Earth\u2019s Tectonic Plates<\/h2>\r\n

Seafloor and continents move around on Earth\u2019s surface, but what is actually moving? What portion of the Earth makes up the \u201cplates\u201d in plate tectonics? This question was also answered because of technology developed during war times - in this case, the Cold War. The plates<\/strong> are made up of the lithosphere.<\/p>\r\n\r\n\r\n[caption id=\"attachment_480\" align=\"alignright\" width=\"350\"]\"A Figure 1. Earthquakes outline the plates.[\/caption]\r\n

During the 1950s and early 1960s, scientists set up seismograph networks to see if enemy nations were testing atomic bombs. These seismographs also recorded all of the earthquakes around the planet. The seismic records could be used to locate an earthquake\u2019s epicenter<\/strong>, the point on Earth\u2019s surface directly above the place where the earthquake occurs.<\/p>\r\n

Earthquake epicenters outline the plates. Mid-ocean ridges, trenches, and large faults mark the edges of the plates, and this is where earthquakes occur (figure\u00a01).<\/p>\r\n

The lithosphere is divided into a dozen major and several minor plates (figure 2). The plates\u2019 edges can be drawn by connecting the dots that mark earthquakes' epicenters. A single plate can be made of all oceanic lithosphere or all continental lithosphere, but nearly all plates are made of a combination of both.<\/p>\r\n\r\n\r\n[caption id=\"attachment_482\" align=\"aligncenter\" width=\"500\"]\"Map Figure 2. The lithospheric plates and their names. The arrows show whether the plates are moving apart, moving together, or sliding past each other.[\/caption]\r\n

Movement of the plates over Earth's surface is termed plate tectonics<\/strong>. Plates move at a rate of a few centimeters a year, about the same rate fingernails grow.<\/p>\r\n\r\n

How Plates Move<\/h2>\r\n[caption id=\"attachment_483\" align=\"alignright\" width=\"450\"]\"Cross-section Figure 3. Mantle convection drives plate tectonics. Hot material rises at mid-ocean ridges and sinks at deep sea trenches, which keeps the plates moving along the Earth\u2019s surface.[\/caption]\r\n

If seafloor spreading drives the plates, what drives seafloor spreading? Picture two convection cells side-by-side in the mantle, similar to the illustration in figure\u00a03.<\/p>\r\n\r\n

    \r\n \t
  1. Hot mantle from the two adjacent cells rises at the ridge axis, creating new ocean crust.<\/li>\r\n \t
  2. The top limb of the convection cell moves horizontally away from the ridge crest, as does the new seafloor.<\/li>\r\n \t
  3. The outer limbs of the convection cells plunge down into the deeper mantle, dragging oceanic crust as well. This takes place at the deep sea trenches.<\/li>\r\n \t
  4. The material sinks to the core and moves horizontally.<\/li>\r\n \t
  5. The material heats up and reaches the zone where it rises again.<\/li>\r\n<\/ol>\r\n

    Check out this animation of mantle convection<\/a>\u00a0and watch this video:<\/p>\r\n