Lesson 3: Subduction and Melting

Key Idea

While uplift pushes rock into the air, subduction drags it into the abyss. This process occurs when a dense oceanic plate slides beneath another plate, carrying its cargo of rocks deep into the mantle.

This is the Earth's mechanism for burial. It effectively removes rock from the cool, low-energy surface environment and forces it down into the high-energy regime of Earth's interior.

Key Idea

Depth equals heat. As rock descends further during subduction, it absorbs increasing amounts of thermal energy from the surrounding mantle.

Eventually, the temperature overwhelms the rock's solid structure, causing a phase change. The solid rock melts into liquid magma. This completes the loop: material that once existed as cold sediment on the ocean floor is returned to a molten state, ready to begin the cycle again.