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Sea Floor Spreading • The process by which new oceanic lithosphere forms as magma rises to the surface and solidifies – Evidence for continental drift • DIVERGENT plate boundaires • Mid-ocean ridges are located where there is sea floor spreading. – Example: Mid-Atlantic Ridge Causes of Tectonic Plate Motion • Changes in density within the athenosphere • Energy comes from center of Earth • Convection currents *important – Heated rock expands and rises (less dense) – Cool rock contracts and sinks (more dense) Convection currents • Definition - transfer of energy by flow of a heated substance – Hot liquids - RISE (less dense) – Cold liquids - SINK (more dense) • Why? When heated molecules expand and are less dense • Interior of the earth (think lava lamp) – Center is hot and liquid magma rises • Less dense – Rises to crust and pushes it • Give convergent and divergent boundaries – Cools and sinks back down to the center • More dense Convection currents https://www.youtube.com/watch?v=ryrXAGY1dmE Awesome video How is it measured? • In centimeters per year • GPS (global positioning system) from satellites – Scientists record the time it takes for GPS ground stations to move a given distance – This allows them to measure the speed of the plates motion Folding • Bending of rocks because of stress • Types – Anticlines: downward • Like a sad face – Synclines: upward • Like a smile face – Monocline: both ends are horizontal Faulting • The surface along which rocks break and slide past each other