Plate Tectonics & Continental Drift

• Earth has multiple tectonic plates that move in different directions, creating various phenomena.
• The lithosphere is broken into tectonic plates that carry continents and parts of the ocean floor.
• Plate tectonics theory states that Earth's lithosphere is made of tectonic plates in slow, constant motion, driven by forces in the mantle.

History of Plate Tectonics

• In the late 1800s, Alfred Wegener hypothesized that continents move, calling it continental drift. Evidence for continental drift included matching land features (mountain ranges of Africa and South America), matching coal fields in Europe and North America, and fossils on different continents.
• Lystrosaurus fossils found in Africa and Antarctica supported continental drift.
• Henry Hess proposed the idea of seafloor spreading to explain continent movement.
• Seafloor spreading occurs as molten material enters along mid-ocean ridges, pushing old crust outward and forming new oceanic crust.
• Evidence for seafloor spreading includes molten material eruptions (volcanoes), magnetic stripes in oceanic rocks, and the ages of oceanic rocks.
• Earth's magnetic poles have reversed many times, recorded in "striped" seafloor rocks.

Causes of Tectonic Plate Movement

• Mantle convection is a mechanism of plate movement, where materials move in currents due to differences in heat and density.
• During convection, heated particles circulate, with hot particles rising and cold particles sinking.
• Ridge push is another theory, where magma rises to form new oceanic crust at mid-ocean ridges, pushing older rock downward and away.
• New rock cools, becomes dense, and falls downward due to gravity.
• Slab pull occurs when dense tectonic plates sink beneath less dense plates, creating a pull on the rest of the plate.
• Subducting plates create the fastest tectonic plate movement.

Types of Tectonic Plate Movement

• Plates move in three main ways: divergent, convergent, or transform plate boundaries.
• Changes in Earth's crust happen along plate boundaries at a rate of one to ten centimeters per year.
• Divergent boundaries occur when two plates move away from each other, often along mid-ocean ridges or as rift valleys on land (e.g., Great Rift Valley in Africa).
• Convergent plate boundary is where two plates collide.
• In continent-continent collisions, plates push against each other, creating mountains.
• In continent-ocean collisions, the oceanic plate sinks beneath the continental plate.
• In ocean-ocean collisions, the denser plate sinks below the less dense plate.
• Transform boundaries involve two plates sliding past each other horizontally, causing friction and earthquakes (e.g., San Andreas Fault).

Effects of Tectonic Plate Movement

• Plate movement causes short-term and long-term changes, including volcanic activity, earthquakes, mountain building, and continent movement over millions of years.
• All continents were once part of a large landmass called Pangaea, which slowly moved apart.
• Energy affects tectonic plate movement, creating mountains through folding, volcanic activity, or faulting.
• Uplift causes land to rise and create mountains (e.g., Appalachian Mountains).
• Divergent and convergent plate boundaries, as well as hot spots, can form volcanoes.
• The Hawaiian Islands were formed through hot-spot activity, where a mantle plume rises through the asthenosphere and lithosphere.
• Tectonic plates move over these fixed plumes, forming volcanoes.
• Stress from plate movements creates breaks in Earth's crust called faults.
• Earthquakes are the release of energy when faulting occurs.

The lithosphere is divided into tectonic plates that move, causing geological phenomena. Wegener's continental drift theory, supported by land features and fossils, was a precursor to plate tectonics. Seafloor spreading explains the movement of continents.