Plate Tectonics and Continental Drift Notes
Sea-Floor Spreading
Sea-floor spreading is the process where new lithosphere forms as magma rises to the Earth's surface at mid-ocean ridges.
Scientists have studied mid-ocean ridges and dated the rocks, verifying that rocks farther from the mid-ocean ridges are older.
This proves that the Atlantic Ocean is being pushed apart and getting larger.
Convection currents in the Earth's asthenosphere are believed to be the force causing the movement of the tectonic plates.
Today, GPS is used to monitor the movement of the Earth's lithosphere.
Types of Plate Boundaries
Divergent Boundary: Plates move away from each other.
Seafloor spreading occurs at mid-ocean ridges (e.g., Mid-Atlantic Ridge).
Transform Boundary: Plates slide past each other horizontally.
The primary source of earthquakes (e.g., San Andreas Fault in California).
Convergent Boundary: Plates collide with each other.
Primary source of volcanoes (e.g., Himalayan Mountains and Pacific "Ring of Fire").
Wegener Redeemed!
Wegener could not provide a mechanism that causes the continents to move apart.
Harry Hess used SONAR technology developed during WWII to discover a mid-ocean ridge in the Atlantic Ocean.
Mid-ocean ridge: A long, undersea mountain range that has a steep, narrow valley at its center, forming as magma rises from the asthenosphere, causing the Earth's lithosphere to lift and separate.
Wegener's Evidence
Alfred Wegener first hypothesized continental drift in 1912.
He noticed that the continents on each side of the Atlantic Ocean appeared to fit like puzzle pieces.
He studied fossils of plants and land animals and noted their existence on separate continents.
Wegener's Evidence Continued…
Wegener noticed similar rocks and mountain ranges across continents. The Appalachian Mountains were once a large mountain range spanning through the Eastern United States and Northern Europe.
Evidence showed similar climates on separate continents millions of years ago, differing from today's climates.
Sea-Floor Spreading
- Sea-floor spreading is the process where new lithosphere forms as magma rises to the Earth's surface at mid-ocean ridges.
- Mid-ocean ridges are underwater mountain ranges where tectonic plates diverge.
- Magma rises from the Earth's mantle at these ridges, solidifying to form new oceanic crust.
- Scientists have studied mid-ocean ridges and dated the rocks, verifying that rocks farther from the mid-ocean ridges are older.
- Rocks near the ridges are younger, indicating continuous formation of new crust.
- Dating methods, such as radiometric dating, confirm the age progression.
- This proves that the Atlantic Ocean is being pushed apart and getting larger.
- As new crust forms, the older crust is pushed away from the ridge.
- This process contributes to the widening of the Atlantic Ocean.
- Convection currents in the Earth's asthenosphere are believed to be the force causing the movement of the tectonic plates.
- Hotter, less dense material rises, while cooler, denser material sinks, creating a circular motion.
- These convection currents exert forces on the overlying tectonic plates, causing them to move.
- Today, GPS is used to monitor the movement of the Earth's lithosphere.
- GPS technology provides precise measurements of the positions and movements of points on the Earth's surface.
- Scientists use GPS data to track the speed and direction of plate movements.
### Types of Plate Boundaries
Divergent Boundary: Plates move away from each other.
- Seafloor spreading occurs at mid-ocean ridges (e.g., Mid-Atlantic Ridge).
- As plates separate, magma rises to fill the gap, forming new crust.
- This process results in the creation of new oceanic lithosphere.
Transform Boundary: Plates slide past each other horizontally.
- The primary source of earthquakes (e.g., San Andreas Fault in California).
- The sliding motion causes stress to build up along the fault line.
- When the stress exceeds the strength of the rocks, it is released as seismic waves, causing earthquakes.
Convergent Boundary: Plates collide with each other.
- Primary source of volcanoes (e.g., Himalayan Mountains and Pacific "Ring of Fire").
- Subduction zones occur where one plate slides beneath another.
- The subducting plate melts as it descends into the mantle, generating magma that rises to the surface and forms volcanoes.
Wegener Redeemed!
- Wegener could not provide a mechanism that causes the continents to move apart.
- His hypothesis was initially rejected due to the lack of explanation for the driving forces behind continental drift.
- Harry Hess used SONAR technology developed during WWII to discover a mid-ocean ridge in the Atlantic Ocean.
- SONAR (Sound Navigation and Ranging) uses sound waves to map the ocean floor.
- Hess's discovery provided evidence for seafloor spreading, supporting Wegener's ideas.
Mid-ocean ridge: A long, undersea mountain range that has a steep, narrow valley at its center, forming as magma rises from the asthenosphere, causing the Earth's lithosphere to lift and separate.
- The rising magma creates new oceanic crust, pushing the existing crust apart.
Wegener's Evidence
- Alfred Wegener first hypothesized continental drift in 1912.
- He proposed that the continents were once joined together in a supercontinent called Pangaea.
- He noticed that the continents on each side of the Atlantic Ocean appeared to fit like puzzle pieces.
- The shapes of the continents, particularly South America and Africa, suggest they were once connected.
- He studied fossils of plants and land animals and noted their existence on separate continents.
- The presence of identical or similar fossils on different continents supports the idea that they were once joined.
Wegener's Evidence Continued…
- Wegener noticed similar rocks and mountain ranges across continents. The Appalachian Mountains were once a large mountain range spanning through the Eastern United States and Northern Europe.
- The geological structures and rock formations match across the Atlantic.
- Evidence showed similar climates on separate continents millions of years ago, differing from