What Is Geothermal Energy? - Definition, Advantages & Disadvantages

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  • 0:00 Geothermal Energy
  • 0:39 Capturing Earth's Heat
  • 2:13 Advantages of…
  • 3:09 Disadvantages of…
  • 3:52 Lesson Summary
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Lesson Transcript
Instructor: Sheila Morrissey

Sheila has a master's degree in geology and has taught middle school through university-level science courses.

In this lesson, we will learn about geothermal energy, including how we capture it and use it. We will discuss the pros and cons of exploiting geothermal energy sources.

Geothermal Energy

The prefix geo-, like you've seen before in the words 'geology' and 'geography', is a Greek work meaning Earth. The term thermal is similar to the word thermometer and thermal underwear, and it means heat. We put the terms together in the word geothermal to describe heat coming from the earth. There are two sources of Earth's heat, or geothermal energy: the leftover heat from the formation of our planet and radiogenic heat, which is the heat resulting from radioactive decay within Earth. Both heat sources are naturally occurring and provide abundant energy that can be harnessed for human energy needs.

Capturing Earth's Heat

Prehistorically, and until recently, people could only make use of geothermal energy that made its way to Earth's surface, primarily as geothermal hot springs used for recreational and medicinal bathing. The oldest known pool created for this purpose was built in China in the 3rd century BCE, during the Qin dynasty. Today, geothermal baths continue to lure relaxing vacationers. The water in these hot springs is warmed as it comes into contact with rocks heated by magma below the earth's surface, so the springs are most common in volcanic areas.

In the 20th century, people started using geothermal energy for electricity generation instead of, or as a supplement to, oil, natural gas, coal, and nuclear power sources. With greater drilling capabilities came the ability to penetrate deep, underground steam reservoirs. Although geothermal energy is present everywhere on Earth, it is still most easily accessible in volcanic areas, which can typically be found above subducting tectonic plate boundaries, where one tectonic plate sinks beneath another, partially melting and creating volcanoes at the earth's surface, such as in Alaska and Japan; near divergent plate boundaries, where tectonic plates pull away from each other and magma rises to the surface, such as in Iceland; and over hot spots, where mantle material rises beneath the crust, such as in Hawaii and Yellowstone National Park. In these areas, magma is found at shallow depths, bringing geothermal heat close enough to the surface to be drilled and captured for our use at geothermal electricity stations.

Advantages of Geothermal Energy Use

Harnessing geothermal energy can have fewer environmental impacts than exploiting other energy sources. As a cleaner resource, there tends to be little airborne emissions from geothermal electricity stations. Highly developed drilling methods safely tap into geothermal energy reservoirs with little risk of releasing geothermal fluids, and the land area over geothermal reservoirs can still be used as farmland.

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