How does magnetism support the theory of seafloor spreading?
Magnetism proves that the seafloor is spreading because the polarity of Earth reverses periodically and the corresponding magnetism of Earth is reflected in the material that rises from the mantle and cools at mid-ocean ridges.
What is sea-floor spreading and what causes it?
Seafloor spreading occurs at divergent plate boundaries. As tectonic plates slowly move away from each other, heat from the mantle’s convection currents makes the crust more plastic and less dense. The less-dense material rises, often forming a mountain or elevated area of the seafloor.
What are the three steps in the process of seafloor spreading?
Terms in this set (7)
- Magma comes out of the rift valley.
- Magma cools to rock and hardens.
- Rock is pushed away as new rock is formed at MOR.
- Oceanic crust and continental crust meet at the trench.
- Oceanic crust bends down under the continental crust.
- Gravity pulls rock towards mantle.
- Rock melts to mantle.
How are magnetism and seafloor spreading related to each other?
Basaltic magma forming at mid-ocean ridges serves as a kind of “tape recorder”, recording the Earth’s magnetic field as it reverses through time. If this idea is correct, alternating stripes of normal and reversed polarity should be arranged symmetrically about mid-ocean spreading centers.
How is the age of the sea floor related to its spreading?
The discovery of such magnetic stripes provided powerful evidence that sea-floor spreading occurs. The age of the sea-floor also supports sea-floor spreading. If sea-floor spreading operates, the youngest oceanic crust should be found at the ridges and progressively older crust should be found in moving away from the ridges towards the continents.
How did scientists discover the spreading of the ocean floor?
The magnetism of mid-ocean ridges helped scientists first identify the process of seafloor spreading in the early 20th century. Basalt, the once- molten rock that makes up most new oceanic crust, is a fairly magnetic substance, and scientists began using magnetometer s to measure the magnetism of the ocean floor in the 1950s.
How does seafloor spreading and subduction affect the Earth?
Seafloor spreading creates new crust. Subduction destroys old crust. The two forces roughly balance each other, so the shape and diameter of the Earth remain constant. Earth’s newest crust is created at sites of seafloor spreading—red sites on this map.