Transition zone (Earth)

Deep inside our Earth lies a special layer. This is called the mantle transition zone. It sits between the upper mantle and the lower mantle. Most people think of the mantle as one big layer. However, it is actually divided into three parts. The transition zone is the middle part of this rocky layer. It is made mostly of a rock called peridotite.

This layer works through changes in pressure. As you go deeper, the weight above grows. This pressure changes how minerals look and act. At 410 km deep, olivine grains rearrange themselves. They form a denser crystal structure because of the weight. Later, at 660 km, ringwoodite changes into new things. These new parts are called bridgmanite and periclase.

Scientists study these deep layers using earthquake waves. They use waves called body waves to see inside. These waves reflect or bend when they hit a boundary. This happens because the rocks change density at certain depths. Scientists also use something called receiver functions. These help show single or double reflections of the waves. This is how we know the layers exist.

There are specific numbers for these deep boundaries. The first change happens at the 410 km discontinuity. The second major change is at 660 km. The depth of these lines can actually change. In cold regions, these boundaries might be deeper. In hot regions, they might be shallower. This is due to the Clapeyron slope.

These changes help us understand how the Earth moves. The change at 660 km creates a viscosity jump. This means the rock becomes harder to move. This jump is important for geodynamical models. Cold material might even pond on this transition. It is like a speed bump for moving rock. This helps us see how the whole Earth works.