Early Earth, Page 14: [Previous Page] [Next Page] [Syllabus] Textbook pages 35 - 53

Heating and Convection of the Earth's Mantle

Why do we see individual plates? What is causing them to move relative to each other? It must be an enormous source of energy. The Earth is much warmer than it should be, if it relys only on the Sun for its heat! There have been other sources of heat energy to the Earth than the Sun.

Decay of Radioactive elements. When the Earth formed, it included some radio-active elements. With time, these elements break down (break apart). The amount of heating, while still significant today, is less than it used to be.

Freezing (Solidifying) of the Earth's Core. The center of the core is now solid, but the outer core is still molten. As it freezes (hardens) it releases energy.

Large Impacts to Earth Luckily, this source of heating is not important anymore.

Frictional Heating due to Settling of Heavy Elements. Most of the heavy elements (Fe/Ni) have now settled to the core.

All of this works to HEAT the MANTLE. But a HOT MANTLE needs to COOL! It does so by convection. Mantle Convection is the mechanism by which continental drift occurs. It works as far as 3,000 km deep into the Earth.

The Mantle is attached to the upper crust. As the mantle pushes up, it spreads the crust creating Mid-Ocean Ridges. In cooler regions of the Mantle, where material is dense and falling back down, subduction zones are created.

Sometimes two continents, which can not subduct, are pushed together. This creates mountains. Sometimes continental or oceanic crusts can be moved across `Hot Spots'. Here, a chain of volcanos are formed (ex. Hawaiian and Aleutian Islands in the Ocean, Yellowstone on land).

Warm water at the surface of the Earth, in part due to a molten mantle, may have had profound effects on the origin and early development of life on Earth.