Mantle Convection

pc: Franklyn Dunbar

The chief instigator behind the dynamic history of the earth’s surface is the mantle. Taking up 83% of the earth’s volume and 63% of its mass, this layers lies between the crust and the core and has a depth dependent gradient of increasing heat and decreasing viscosity. The upper portion is relatively cold and viscous (5-660 Km), while the lower layer is fluid and molten (660-2885km). This difference in temperature has resulted in an exchange of heat energy between the upper and lower layers, or convection. Mantle convection is driven by the decay of radioactive isotopes that began during earth’s formation. Through convection currents, heat is transported with circulating material from the fluid portions of the mantle to the top. At plate boundaries along the ocean floor, these currents push plates apart.  This spreading force is what pushes one plate below another at what is called a “subduction zone”. It is this phenomenon that drives tectonic activity.

These photos were created by the USGS