7. Earth as
a Heat Engine
Expedition Menu
Thermal Hot Springs
So why is the Earth such
a dynamic planet?
Heat, my friend, heat!
The picture to the left shows the release of steam from geothermal plants in Santa Rosa -- geothermal plants tap the heat within the Earth to produce energy in the form of electricity.
The heat trapped within the Earth, which was generated during its formation billions of years ago and through the decay of radioactive elements with rocks, is trying to escape, much like heat also escapes out the top of a beaker of boiling water.
The heat in the interior of the Earth produces convection in the outer core and mantle of the Earth. Convection is the transport of mass by heat -- which affects the density (mass/volume) of material.
To understand this concept -- consider the following question --
Why does a hot air balloon rise?
Heat produces an expansion of the air in the balloon making it less dense than the cool air outside of the balloon. Remember density is mass per volume or
Density = mass/volume
So by heating the air, the volume of air increases, while the mass of the air stays the same, consequently the density must decrease
The earth's gravity field, then allows the less dense, hot air balloon to rise and the cool, surrounding air with a higher density to sink.
This type of movement, called convection, also occurs within the Earth as hot, less dense portions of the mantle rise and displace cooler, denser rocks, which then sink into the mantle -- in summary the cooler, dense rocks sink in the mantle, whereas the warmer rocks within the mantle rise by a process called mantle convection (shown by red arrows in the diagram at the left).
So clearly convection plays an important role in the influencing the dynamic nature of the Earth. Later we will discuss the importance of the sinking, cold portions of plates along the surface of the Earth (shown in gray).
Created By:
Don Reed
Dept. of Geology
San Jose State University
©Copyright 2008
Last Updated on
Sept. 22, 2008
Evidence of the dynamic nature of the Earth is mantle convection with:
a) warm rocks of the mantle sinking,
b) cool rocks of the mantle rising,
c) warm portions of the mantle are less dense and therefore rise through cooler, more dense portions of the mantle