Answer:

1.) Geologists have hypothesized that the movement of tectonic plates is related to convection currents in the earth's mantle. Tremendous heat and pressure within the earth cause the hot magma to flow in convection currents. These currents cause the movement of the tectonic plates that make up the earth's crust.

2.) Convection currents drive the movement of Earth's rigid tectonic plates in the planet's fluid molten mantle. In places where convection currents rise up towards the crust's surface, tectonic plates move away from each other in a process known as seafloor spreading (Fig. 7.21).

3.) A mid-ocean ridge or mid-oceanic ridge is an underwater mountain range, formed by plate tectonics. This uplifting of the ocean floor occurs when convection currents rise in the mantle beneath the oceanic crust and create magma where two tectonic plates meet at a divergent boundary.

4.) The process by which ocean floor sinks beneath a deep-ocean trench and back into the mantle is called subduction (sub duk shun). ... But as it moves away from the mid-ocean ridge, it cools and becomes more dense. Eventually, as shown in Figure 19, gravity pulls this older, denser oceanic crust down beneath the trench.

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