Today’s Wonder of the Day was inspired by Cecilia. Cecilia Wonders, “Where does geothermal energy come from?” Thanks for WONDERing with us, Cecilia!

Do you look forward to the day when you'll be able to drive your own car? Just think of the freedom! You'll be able to go where you want whenever you want! Of course, there's one downside to that freedom: you'll have to pay to fill up your gas tank.

With the price of gasoline inching upward year after year, you might start thinking more and more about renewable sources of energy. After all, fossil fuels will one day be gone. Future generations must develop new technologies that will allow them to harness renewable energy sources to be able to continue to fuel our modern lives.

You're probably aware of some popular renewable energy sources, such as wind and hydroelectric power. Did you realize, though, that there's a source of renewable energy right underneath your feet? What are we talking about? Geothermal energy, of course!

Geothermal energy gets its name from the Greek words "geo" and "therme," which mean "earth" and "heat." Simply put, geothermal energy is energy in the form of heat inside the Earth. Did you realize that there's heat inside the Earth? In fact, the farther you go inside the Earth, the hotter it gets.

Earth's inner core can reach temperatures approaching 10,800º F. That's about the same temperature as the surface of the Sun! Between the inner core and the surface of the Earth, there are thousands of miles of countless layers of superheated substances, including molten rock, water, and steam.

Evidence of geothermal energy can be seen on Earth's surface in many areas. Volcanoes that spew lava, geysers that shoot steam and hot water into the sky, and hot springs that offer a soothing soak are all examples of the heat inside the Earth rising to its surface.

Some of the heat within the Earth is a remnant of the events that formed the Earth over four billion years ago. The remainder of the heat comes from the constant decay of radioactive elements deep inside the Earth.

Those who research and develop geothermal energy seek to tap these sources of heat inside the Earth to both heat homes directly and generate electricity. Since the inside of the Earth keeps producing heat, geothermal energy is a renewable energy source that can be relied upon for the foreseeable future.

In areas with hot springs or geothermal reservoirs near the surface, hot water can be pumped directly to homes and businesses to heat them. In other areas, geothermal heat pumps circulate water through loops of pipes buried in the ground where the temperature stays a constant 50º-60º F all the time. These systems can both heat homes and businesses in the winter and cool them in the summer.

Engineers have even found ways to pipe steam and hot water from deep underground to geothermal power plants to produce electricity. Compared to other types of energy, geothermal energy is considered to be more efficient, cost-effective, and cleaner than burning fossil fuels. Today, the United States is the world's largest producer of geothermal energy, but experts believe that current production levels are only the tip of the iceberg of what is possible.

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Join us in Wonderopolis tomorrow for a Wonder of the Day that’s not made of wood, glass, or metal!