ShareEarth's Structure - How Many Licks Does it Take to Get to the Center?
Earth's Mantle
Moving
beneath the crust we find the mantle.
No one has actually been to the mantle but scientists have a good idea
of what it's like. Do you think that mantle material would be more or
less dense than the crust? Answer (drag your mouse over the link to see the answer.)
The mantle is divided into two regions, the upper and lower sections. It makes up almost two-thirds of Earth's mass and is about 2,900 km thick. Directly below the upper section is the asthenosphere. Heat and pressure cause a small amount of melting to occur in this region. While still solid, the asthenosphere is able to flow. The ability of a solid to flow is called plasticity. Since the asthenosphere is more liquid than the rest of the mantle, the upper section is able to "float" on it.
When the material in the asthenosphere is heated, it becomes less dense and it then rises. While the cooler material that is more dense tends to sink. Circulating currents carry the warmer material up and the cooler material down. These circular currents in the asthenosphere are called convection currents. The circulating convection currents cause the plates to move.
