Continental Drift
* Concept: The theory that the continents have moved over time, changing their positions on Earth's surface.
* Evidence:
* Matching coastlines: The shapes of continents, particularly South America and Africa, fit together like puzzle pieces.
* Fossil distribution: Identical fossils are found on widely separated continents, suggesting they were once connected.
* Rock types and structures: Similar rock formations and geological structures are found on different continents.
* Mechanism: The mechanism for continental drift was initially unclear.
Seafloor Spreading
* Concept: The process by which new oceanic crust is formed at mid-ocean ridges and then moves away from the ridges as the seafloor spreads.
* Evidence:
* Magnetic striping: The magnetic field of the Earth flips over time. This leaves a record of reversals on the seafloor, creating symmetrical patterns of magnetic stripes.
* Age of seafloor rocks: Rocks closer to mid-ocean ridges are younger than rocks further away.
* Heat flow: Higher heat flow is observed at mid-ocean ridges.
* Mechanism: Seafloor spreading is driven by the movement of tectonic plates, which is powered by convection currents in the Earth's mantle.
Key Differences:
* Focus: Continental drift focuses on the movement of continents, while seafloor spreading focuses on the formation and movement of new oceanic crust.
* Mechanism: While continental drift didn't initially explain the mechanism, seafloor spreading provides the mechanism for both continental drift and the movement of tectonic plates.
* Scale: Seafloor spreading occurs on a larger scale, creating new ocean basins and driving the movement of continents.
Relationship:
Seafloor spreading is the mechanism behind continental drift. The creation of new ocean crust at mid-ocean ridges pushes the continents apart, causing them to drift across the Earth's surface.
In essence, continental drift is what we see on the surface, while seafloor spreading is the underlying process driving that movement.
