In the 1960s, scientists found evidence that new material is erupting along mid-ocean ridges. The scientists dived to the ocean floor in Alvin, a small submarine that was built to withstand the pressures from four kilometres down in the ocean. In a ridge’s central valley, Alvin’s crew found strange rocks shaped like pillows. This rock can only form when molten hardens quickly after erupting under water. This is evidence that molten material has erupted over and over along the mid-ocean ridge.
Evidence From Magnetic Stripes
Scientists discovered that the rocks that make up the ocean floor lie in a pattern of magnetised stripes. These stripes hold a record of the Earth’s magnetic field. The rock of the ocean floor contains iron. The rock began as molten material that cooled and hardened. As the rock cooled, the iron bits inside lined up in the direction of Earth’s magnetic poles and is fixed in that location. The locked iron bits are called magnetic memory.
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The Glomar Challenger, a drilling ship built in 1968, gathered the samples from the Mid-Atlantic Ridge. From the samples gathered, scientists could determine the age of the rocks that were given to sample. The scientists also found that the further away the sample was from the ridge the rock was older than the samples taken from the rocks taken closer to the middle of the Mid-Atlantic.
Distribution of Earthquakes and Volcanoes
Diverging plates
Diverging plates is when the plates move away from each other. In the space between the plates, there is magma that flows up which then cools and hardens, which forms mid-ocean ridges. The Pacific Ocean has many mid-ocean ridges. It is growing wider by about 18cm per year as the plates diverge and the mid-oceanic ridge builds