The Theory of Plate Tectonics Ch. 14 Lesson 3

The Plate Tectonics Theory The oceanic crust continues to form at mid-ocean ridges. So why doesn’t the surface area of Earth increase? Because the older crust is destroyed! But how?

The Plate Tectonics Theory Plate tectonics – Earth’s surface is made of rigid slabs of rock, or plates, that move with respect to each other. This new theory suggested that Earth’s surface is divided into large plates of rigid rock. Each plate moves over Earth’s hot and simi-plastic mantle

The Plate Tectonics Theory Geologists use the word tectonic to describe the forces that shape Earth’s surface and the rock structures that form as a result

The Plate Tectonics Theory This theory provides an explanation for the occurrence of earthquakes and volcanic eruptions as well as plate movement! https://vimeo.com/14258924

What’s Happening With These Plates? When plates separate on the sea floor, earthquakes result! When plates come together, one plate can dive under the other causing earthquakes and creating a chain of volcanoes When the plates slide past each other earthquakes can result

Tectonic Plates These plates are “floating” on top of a hot and semi-plastic mantle.

The pacific plate is the largest plate The Juan de Fuca Plate is the smallest Note the boundaries in the middle of the ocean

The Lithosphere Earth’s outermost layers are cold and rigid compared to the layers within Earth’s interior The cold and rigid outermost rock layer is called the lithosphere It is made up of the crust and the solid, uppermost mantle

The Lithosphere Earth’s tectonic plates are large pieces of the lithosphere. These lithosphere plates fit together like ginormous puzzle pieces.

The Asthenosphere The layer of Earth below the lithosphere is the asthenosphere This layer is so hot that it behaves like a plastic material

The Asthenosphere The plates move on top of the hotter, plastic mantle material beneath The interactions between the lithosphere and asthenosphere help explain plate tectonics

Plate Boundaries There are 3 types of plate boundaries: Divergent plate boundaries Transform plate boundaries Convergent plate boundaries

Divergent Plate Boundary Forms where 2 plates separate Mid-Ocean ridges Can happen on continents (East African Rift)

East African Rift

Transform Plate Boundary Forms where 2 plates slide past each other As they move past each other the plates get “stuck.” Eventually the stress builds up and the rocks break, suddenly moving apart. This rapid energy release between plates is an earthquake San Andreas Fault in California

San Andres Fault California

Convergent Plate Boundary Forms where 2 plates collide The denser plate sinks below the more buoyant plate in a process called subduction The area where a denser plate descends into Earth along a convergent plate boundary is called a subduction zone

Convergent oceanic + continental When an oceanic plate and a continental plate collide, the denser oceanic plate subducts under the edge of the continent This creates a deep ocean trench. A line of volcanoes forms above the subducting plate on the edge of the continent.

Deep Ocean Trench

Convergent oceanic + oceanic This can also occur between two oceanic plates! The older and denser oceanic plate will subduct beneath the younger oceanic plate. This creates a deep ocean trench and a line of volcanoes called an island arc

Convergent continental + continental When 2 continental plates collide, neither plate is subducted Mountains form from the uplifted rock Himalayas in southern Asia

Himalayas in Southern Asia

Evidence for Plate Tectonics Back in Wegener’s day we didn’t have the technology to track plate movement Today, scientists can measure how fast continents move using satellites! (GPS system)

Plate Motion Convection Currents- the circulation of material caused by differences in temperature and density Plate activity is directly related to convection in the mantle

Plate Motion Radioactive elements, such as uranium, thorium, and potassium, heat Earth’s interior. When the materials such as solid rock are heated, they expand and become less dense. Hot mantle material rises upward and comes in contact with Earth’s Crust Thermal energy is transferred from hot mantle material to the colder surface above. As the mantle cools, it becomes denser and then sinks, forming a convection current. These currents in the asthenosphere act like a conveyor belt moving the lithosphere above

Plate Motion Radioactive elements, such as uranium, thorium, and potassium, heat Earth’s interior. When the materials such as solid rock are heated, they expand and become less dense. Hot mantle material rises upward and comes in contact with Earth’s Crust Thermal energy is transferred from hot mantle material to the colder surface above. As the mantle cools, it becomes denser and then sinks, forming a convection current. These currents in the asthenosphere act like a conveyor belt moving the lithosphere above

Forces Causing Plate Movement pg. 517 Basal Drag – Gali, Orli, Avigayil R. Ridge Push – Addi, Shmuel, Neil Slab Pull – David, Ariel and Marc , Sara Writers: Hanna, Sigal, Avigayil L.