Circulating Heat

Part of Hall of Planet Earth.

View of the Circulating Heat section of the Hall of Planet Earth with the mantle convection model at the center AMNH/D. Finnin

Deep beneath our feet is a 2,900-kilometer-thick (1,800-mile) layer of mostly solid rock called the mantle. The mantle flows slowly due to convection. In convection, hotter rocks, which have relatively low densities, rise, while cooler rocks with higher densities sink. In this globe, the hottest portions of the mantle (yellow) are rising toward the surface and cooler portions (red) are sinking toward the core.

 

 

Hawaiian Islands
The Hawaiian Islands formed over a rising plume of hot rock. Near the surface, rock melts into magma, feeding the volcanic island chain.
The Layered Earth panel
Earth is mostly mantle--it makes up 84% of the planet's volume! Earth’s interior is divided into layers. The crust and upper mantle make up the rigid, relatively cool lithosphere. This layer is broken up into tectonic plates that are carried by the convecting mantle. The mantle is made mostly of solid rock and is so hot that it convects, flowing 2 to 3 centimeters (about 1 inch) per year. The outer core is composed of liquid iron-nickel alloy that flows, creating Earth’s magnetic field. The inner core is solid metal. No one knows if the inner core is convecting.
"Where does the heat come from?" panel
For convection to occur there must be a source of heat. The Sun’s energy ultimately drives convection in the atmosphere and ocean—but where does the heat driving convection inside Earth come from? Radioactive Decay (60-80%) Most of Earth’s internal heat appears to come from the decay of the radioactive isotopes of uranium, thorium and potassium. Primordial Heat (20-30%) At some point early in its history, Earth was probably entirely molten. Heat left over from that period is still present deep within Earth. Tidal Friction (up to 10%) The gravitational attraction between Earth and the Moon slightly deforms our planet, generating friction and thus, heat.
Convection in the mantle has effects we can observe on the crust. On the globe here, the hottest parts of the mantle (yellow) stretch toward the surface, where they can cause volcanic hotspots and rifts between plates. Cooler rocks (red) sink, drawing slabs of the lithosphere down to create subduction zones. Extreme heat in Earth's interior causes solid rock to flow without melting. Instead, the rock is "ductile," meaning it moves by stretching and folding instead of breaking. Movement of the mantle carries pieces of Earth's rigid lithosphere around the globe, creating earthquakes, mountains and other surface features. The solid mantle flows at about the same rate as a human fingernail grows, or several centimeters per year.

In This Section

Exhibit How to read the mantle The globe in the center shows present-day mantle convection based on studies of how tectonic plates have moved over the last 200... Exhibit Mantle model This globe is a snapshot of mantle convection—a process that occurs slowly, over millions of years.