Seafloor spreading provides the mechanism by which continental drift occurs; as new oceanic crust is created at mid-ocean ridges, it pushes older crust away, effectively moving continents along with it.
The Connection Explained
The theory of continental drift, initially proposed by Alfred Wegener, suggested that continents were once joined together in a supercontinent called Pangaea and have since drifted apart. However, Wegener lacked a convincing mechanism for how this drift occurred. Seafloor spreading, discovered later, filled this gap.
Seafloor Spreading: The Engine of Continental Drift
Here's how seafloor spreading drives continental drift:
- Mid-Ocean Ridges: Molten rock (magma) rises from the Earth's mantle at mid-ocean ridges.
- New Crust Formation: This magma cools and solidifies, forming new oceanic crust.
- Spreading and Pushing: As new crust forms, it pushes the older crust away from the ridge. This is seafloor spreading.
- Continental Movement: Because continents are embedded in the Earth's lithosphere (which includes both oceanic and continental crust), they are carried along with the spreading seafloor. This is continental drift.
- Subduction: As oceanic crust spreads, it eventually collides with continental crust or another section of oceanic crust. Because oceanic crust is denser, it subducts (sinks) beneath the less dense continental crust or the other oceanic crust. This process recycles the oceanic crust back into the mantle.
Analogy
Think of a conveyor belt. The conveyor belt is the spreading seafloor, and the continents are objects sitting on the conveyor belt. As the conveyor belt moves, the objects (continents) move along with it.
Supporting Evidence
The relationship between seafloor spreading and continental drift is supported by:
- Age of Oceanic Crust: The youngest oceanic crust is found near mid-ocean ridges, and the age increases with distance from the ridge. This directly supports the idea of seafloor spreading.
- Magnetic Stripes: Magnetic minerals in the oceanic crust align with the Earth's magnetic field when the crust cools. The Earth's magnetic field reverses periodically, creating symmetrical magnetic stripes on either side of mid-ocean ridges. This further validates the seafloor spreading process.
- Distribution of Earthquakes and Volcanoes: The locations of earthquakes and volcanoes often coincide with plate boundaries, where seafloor spreading and subduction are active.
Continental Drift: From Theory to Fact
Seafloor spreading provided the missing piece of the puzzle that turned Wegener's theory of continental drift into the widely accepted theory of plate tectonics. Plate tectonics explains the movement of the Earth's lithosphere, which is divided into several plates, and how these plates interact with each other.
