The land that is pulled into the mantle along the subduction zone turns into magma as a result of being heated by the Earth’s core. Thus, slab pulls feed the new Earth that is created along the mid-ocean ridge.
Both the mid-ocean ridge and slab pull are the result of convection currents that occur within the mantle below the ocean floor.
Convections currents are a result of temperature and density differences. The inner core of the Earth is extremely hot. The heat from core causes the bottom of the mantle to warm up. As the temperature of particles within the mantle increases, the particles gain kinetic energy. Kinetic energy is the energy of movement. Thus, the particles begin to move more and faster. This causes the particles to move away from one another. As a result of the increased distance between the particles, the density of the substance decreases. Thus, the warmed particles at the bottom of the mantle begin to rise. As the particles move away from the heat source of the Earth’s inner core, they lose kinetic energy. As the particles begin to slow down, they contract. Thus, the density of the particles increases and they sink back towards the bottom of the mantle. The rising and falling of the particles due to temperature and density differences continues and creates a cycle that is known as a convection current.
The mid-ocean ridge occurs along a divergent boundary of two tectonic plates. Each side of the mid-ocean ridge resides over a convection cell of the magma within the mantle. The convection cells that are on either side of the divergent boundary move in opposite directions. The tectonic plates are moved apart from one another when the convection cell move upwards after begin warmed by the Earth’s core. As the plates move apart, the magma from the mantle rises between the crack. As the magma rises to the surface, it is cooled. In this way, new Earth is formed along the mid-ocean ridge.
Slab pulls occur along the opposite ends of the convection cells that push the tectonic plates of the mid-ocean ridge apart. At this end, the convection cells have cooled and are moving downward. The weight of this denser crust pulls this end of the plate downward into the mantle at what is called the subduction zone.