Theory of plate tectonics

The Theory of Plate tectonics States that pieces of the Earth’s lithosphere are in constant slow motion driven by convection currents in the mantle caused by radioactive decay in the core.

The theory of plate tectonics Earth’s outer shell is broken into thin, curved plates Radioactive decay in the Earth’s core provides the heat that drives convection currents in the mantle This convection causes the plates to move across the lithosphere Most earthquakes and volcanic eruptions occur at plate boundaries Theory of plate tectonics was not fully complete until 1970, parts of it are still hotly debated in the geological community.

Tools used to measure plate tectonics Sonar Mapping Seismometers Deep Sea Drilling Submersibles

Sonar mapping The Navy mapped with seafloor with echo sounding (sonar) to find and hide submarines during WWII and the Cold War Maps Showed: Oceanic Ridges: submerged mountain ranges Fracture Zones: cracks perpendicular to ridges Trenches: narrow, deep gashes Abyssal Plains: vast flat areas Seamounts: drowned undersea islands Rocks found at the seafloor included only basalt, gabbro, and serpentinite No continental materials found

Cascade Trench

seismometers Measure earthquakes along tectonic plates Developed during WWII to monitor Soviet nuclear tests Recorded every moderate to large earthquake on the planet Seismologists found that activity happens in narrow bands By 1950, seismometers had been deployed in over 40 allied countries and were recording data 24/7/365.

Bands of Seismicity – mostly at trenches and ridges

submersibles In the 1960s, scientists began using deep sea submersibles to take pictures of underwater volcanoes.

Deep Sea Drilling In 1968, The Glomar Challenger drilled holes in the Atlantic ocean floor and brought back rock samples These samples showed that rocks get older as you move away from the center of the spreading center

Seafloor spreading Molten material rises from the mantle and erupts and spreads out pushing older rock to both sides Occurs at oceanic divergent boundaries Occurs mostly at the Mid Oceanic Ridge Plates are moving away from each other Magma rises along a rift zone and spreads out at the surface This surface contains new sea floor and undersea volcanoes Age of the rocks increases as you move away from the rift zone

Evidence for tectonic plates: magnetic stripes As magma cools at divergent boundaries on the seafloor, crystals “record” the direction of the current magnetic field. These magnetic reversals are recorded in “stripe” patterns on the seafloor. These magnetic stripes show that the seafloor has been spreading apart over time. The magnetic field has reversed several times in Earth’s history.

subduction Process by which the ocean floor sinks beneath a deep ocean trench and back into the mantle Occurs at convergent boundaries One plate slides beneath another Seafloor crust is “recycled” back into the mantle Occurs in relation to spreading so that the Earth is not growing or shrinking

Tectonic plates on modern earth

The theory of plate tectonics States that pieces of Earth’s lithosphere are in constant motion driven by convection currents in the mantle caused by heat from the core. Earth’s outer shell is broken into thin, curved plates Radioactive decay in the Earth’s core provides the heat that drives convection currents in the mantle This convection causes the plates to move across the lithosphere Most earthquakes and volcanic eruptions occur at plate boundaries

Three types of plate motions Divergent: plates move away from each other Convergent: plates move toward each other, one goes underneath Transform: plates slide next to each other in opposite directions