Plate Tectonics and Continental Drift

• All continents were joined approximately 300 million years ago in a supercontinent called Pangaea.
• Pangaea split into smaller pieces over millions of years, resulting in today's continents.
• Continents are still moving, though very slowly, at about the same speed as fingernails grow.
• The Earth's crust sits on a mantle of hot, flowing rock.
• Heat from deep inside the Earth makes the mantle move, pushing continents like icebergs on water.

Evidence of Continental Drift

• Continents such as South America and Africa appear to fit together like puzzle pieces.
• Fossils of identical ancient plants and animals exist on continents now far apart.
• Similar rock layers and mountain ranges are found on separated continents.
• Glaciers found in warm regions like Africa indicate these areas were once colder.
• Alfred Wegener first proposed Continental Drift in 1912, but couldn't explain how the continents moved.
• Plate tectonics explains the movements of Earth's crust, substantiating Wegener's theory later on.

Seafloor Spreading

• Mid-ocean ridges are massive underwater mountain ranges where magma rises through Earth's crust.
• As magma cools on the surface, new oceanic crust is formed.
• This subsequently pushes the older crust away, making the seafloor spread.
• This process repeats over time, as more magma rises, creating new crust.
• In turn, this causes the ocean floor to gradually move outward, carrying continents.

Evidence for Seafloor Spreading

• As new rock forms, it records Earth's magnetic field, which flips every few hundred thousand years.
• Matching patterns of magnetic stripes on both sides of a ridge prove the seafloor spreads out.
• Rocks near mid-ocean ridges are younger, while rocks farther away are older, showing formation of new rock.
• On the opposite side of the ocean, old oceanic crust is forced under continents.
• It then melts back into the Earth at deep trenches through a process called subduction.
• Seafloor Spreading, a main force behind plate tectonics, shows the continents move.
• Earth's crust is constantly recycled with new crust forming at mid-ocean ridges, and old crust being destroyed at deep trenches.

Magnetic Banding

• The Earth's magnetic field switches direction roughly every few hundred thousand to millions of years.
• Magma rises and cools to form new oceanic crust at mid-ocean ridges.
• The rock contains magnetic materials aligned with Earth's magnetic field at the time of cooling.
• As magma rises, it pushes older rock away, forming mirror-image stripes of magnetized rock on both sides of the ridge.
• These stripes alternate between normal and reversed magnetic directions, forming magnetic banding.
• Scientists use these stripes as evidence for seafloor spreading, thus affirming plate tectonics.

Change in the ocean floor

Subduction (Old Ocean Floor Disappears)

• On the other side of the ocean, old oceanic crust is forced under another plate at subduction zones.
• The old crust sinks into the mantle, where it melts and recycles back into the Earth.
• This process prevents the ocean floor from becoming too large.

Earthquakes and Volcanoes

• Plate movement, whether colliding, pulling apart, or sliding, causes earthquakes.
• Magma rising through cracks forms underwater volcanoes, sometimes creating new islands (like Hawaii).

Erosion and Sediment Build-Up

• Sediment layers form from sand, mud, and dead marine life settling on the ocean floor.
• Currents, waves, and underwater landslides can shift and reshape the seafloor.

Rising and Falling Sea Levels

• When sea levels rise, the ocean floor gets covered with water.
• Conversely, when sea levels drop parts of the ocean floor become exposed, forming like the Bering Land Bridge connecting Asia and North America.

Divergent Boundary

• Two tectonic plates move apart at a divergent boundary, forming new crust.
• As the Earth's outer layer, the lithosphere, forms, the tectonic plates slowly move away from each other at the divergent boundary.
• As plates separate, magma rises from beneath the surface, filling the gap.
• Fresh ocean floor or land is created when the magma cools and hardens.

Location of Divergent Boundaries

• Most Divergent boundaries are underwater, like the Mid-Atlantic Ridge
• Magma rises and cools pushing the seafloor apart, causing seafloor spreading.
• Rift valleys are created when divergent boundaries occur on land, such as the East African Rift.
• Over millions of years, these valleys may completely split, allowing ocean water in and forming new seas.
• Crust cracks and shifts inducing earthquakes are a result of plate movement.
• Magma rising to the surface causes underwater volcanoes or volcanic islands.
• As new rifts grow, continents can split apart entirely to create new oceans.
• The Mid-Atlantic Ridge, a massive underwater mountain range is where the Atlantic Ocean is gradually growing due to seafloor spreading.

Convergent Boundary

• Mountains, volcanoes, and deep ocean trenches are produced at Convergent Boundaries.
• Two colliding or pushing tectonic plates form a Convergent boundary.
• Plate collisions can result in subduction, where one plate sinks under the other, thus creating trenches and volcanoes.
• Convergent collisions can form mountains, where plates push up.

Types of Convergent Boundaries

Oceanic-Continental Convergence (Ocean Plate vs. Land Plate)

• The denser oceanic plate descends under the lighter continental plate.
• Deep ocean trenches and land volcanoes are a by product of this process called subduction.
• For example, the Pacific Plate sinks under South America, forming the Andes Mountains and the Peru-Chile Trench.

Oceanic-Oceanic Convergence (Two Ocean Plates Collide)

• The byproduct of one oceanic plate sinking under the other are deep ocean trenches and volcanic island chains.
• For example, Mariana Islands and the Mariana Trench form from this process

Continental-Continental Convergence (Two Land Plates Collide)

• Light land plates, not able to sink, create large mountains as the continents move together.
• For example, the Himalayas, which include Mount Everest, formed by the collision of India's plate with Asia.
• Pressure between the plates triggers earthquakes.
• Sinking and melting of a plate causes magma to rise and form volcanoes.
• Convergent boundaries construct significant mountain ranges and the ocean's deepest regions.

Causes of plate motion

• Tectonic plates are in constant motion at a few centimeters per year.
• The source of plate motion is within the Earth, due to heat and gravity.

Convection Currents

• The mantle circulates in currents called convection currents.
• Hot, less dense rock rises from Deep inside the Earth.
• Plates are pushed and pulled as the rock it cools and sinks back down at surface.

Ridge Push

• Magma rises and forms new rock at mid-ocean ridges.
• New rock drives the older rock, away causing plates to move apart like toothpaste being pushed from a tube.
• A sinking plate pulls the remainder of the plate down with it at subduction zones.
• Gravity pulls the plate deeper into the Earth.
• This is one of the strongest forces driving plate movement.

The downhill theory

• Slab Pull occurs as gravity pulls tectonic plates downhill at subduction zones.

Explore the evidence and mechanisms behind plate tectonics and continental drift. This includes seafloor spreading, continental movement, convergence zones, and the concept of Pangaea. Understand the driving forces and geological features associated with these processes.