Seafloor spreading is a theory that oceanic crust forms along submarine mountain zones, known collectively as the mid-ocean ridge system, and spreads out laterally away from them. This idea played a pivotal role in the development of the theory of plate tectonics, which revolutionized geologic thought during the last quarter of the 20th century.
What is it?
- According to this idea, the intense heat created by radioactive chemicals in the mantle (100-2900 km below the earth’s surface) seeks a way out and causes convection currents to emerge in the mantle.
- Oceanic ridges occur on the seafloor where the rising limbs of these currents meet, while pits form where the failing limbs meet.
- New material is added to the ocean floor, while older materials are pushed away from the crest.
- As molten material erupts from the mantle, it spreads out and pushes older rocks to the sides of the fissure, a new ocean floor emerges along cracks in the ocean crust.
- The process of sea-floor spreading continues to add additional ocean floor.
- Sea-floor spreading is also supported by the age of the seabed. If sea-floor spreading is active, the youngest oceanic crust should be found along the ridges, with older crust appearing as one moves away from the ridges and closer to the continents. This is the situation. Older ocean floors have been devastated by subduction in deep-sea trenches, according to the oldest known ocean floor, which is around 200 million years old.
- In the 1960s, magnetic surveys of the ocean floor showed symmetrical patterns of magnetic “bands” (zebra stripes) anomalies running parallel to midoceanic rifts. Different seas show the same trends in regard to midoceanic rifts. The magnetic anomalies are consistent with occurrences of magnetic reversals observed on land, suggesting that the andesitic rocks that create new oceanic crust in the rift valley’s tensional setting record the earth’s magnetic field as they cool.
- Seismic studies show that earthquakes occur along the rift valley of a midoceanic ridge and the crosscutting fractures that offset it, adding to the evidence for sea floor spreading. Only transform faults, the areas of the fracture zone lying between the offset sections of a ridge and rift valley, are affected by rift valley earthquakes. Transform faults are the only places in the fracture zone where pieces of the oceanic crust flow in opposite directions because of the way the sea floor extends (away from both sides of a midoceanic ridge). The fact that earthquakes are concentrated in the transformfault portions of the fracture zones adds to the theory that the ocean crust is migrating away from a midoceanic ridge.
How to structure:
- Give an intro about sea floor spreading theory
- Explain in detail, with figures
- Discuss the evidences found
- Mention any recent news associated