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.

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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.

As an alternative to oil, natural gas, and coal, geothermal electricity produces far fewer carbon emissions. It, therefore, does not contribute as much to greenhouse gas production and the resulting climate change. Unlike fossil fuels, which require millions of years of heat and pressure to produce, geothermal energy is considered to be a renewable resource. The earth’s heat sources are limitless on the timescales of human life, and we need only water in contact with this heat to produce steam to capture for our electricity consumption.

Disadvantages of Geothermal Energy Use

Even though geothermal energy is considered a renewable energy resource, it is still possible for us to use up the water resources found near shallow heat sources faster than they can be replaced naturally. In addition, like the exploration of any other resource, seeking geothermal energy for our energy needs requires drilling and building electricity stations. An increased reliance on electrical power increases our need to build, which can be considered an eyesore in otherwise beautiful, volcanic areas. This brings us to the biggest current disadvantage to geothermal energy, which is that geothermal energy is most readily accessible in volcanic areas, but in other areas is not possible or economically viable to capture.

Lesson Summary

Geothermal energy is heat emanating from the earth, originating from the planet’s formation and from radioactive decay within the earth. Geothermal energy heats hot springs at the earth’s surface, which have long been used by humans. More recently, people have used geothermal energy for electricity generation by tapping into underground steam reservoirs. The greatest advantage of geothermal energy use is that it tends to be cleaner than other energy sources. It can also be considered a renewable resource. However, it is possible to use up water resources faster than they can naturally be replenished. The greatest disadvantage to geothermal energy use is that it is only readily available in volcanic areas.