What if we used heat from inside Earth?

The ground under your feet feels cool. But deep down, it is very hot!

What if we used that heat to warm our homes and make electricity?

Dig deep enough anywhere on Earth and the rocks get hotter and hotter. In some places that heat reaches the surface on its own, in steaming hot springs and spouting geysers.

So here is a thought experiment: what if we used this heat from inside Earth much more? It never needs to be shipped in, and it keeps flowing day and night in any weather. You can explore three ways people already use it: volcanic places like Iceland, hot springs, and heat pumps that use the steady warmth just under the ground.

Geothermal resources are reservoirs of hot water and steam below the surface, reached by wells from a few feet to several miles deep, plus the steady temperature of the shallow ground itself (DOE).

The thought experiment asks how far this resource could reach. High-temperature reservoirs that can drive turbines are concentrated in particular geological settings, but low-temperature heat for warming buildings exists almost everywhere. The answer depends on which kind of geothermal use you mean.

In Iceland, hot water from underground warms most houses.

In some places, underground steam spins machines that make electricity.

Some countries already rely on Earth's heat. The U.S. Energy Information Administration (EIA) says a district heating system, which pipes hot water to many buildings, heats most of the buildings in Reykjavik, Iceland. In Kenya, geothermal power plants made about 43 percent of the country's electricity in 2022, the biggest share of any country.

In the United States, geothermal power plants in seven states made about 0.4 percent of the country's large-scale electricity in 2025. Most of it came from California.

EIA: in 2022, 25 countries generated about 92 billion kWh of geothermal electricity. Indonesia led with about 17 billion kWh (about 5 percent of its generation); Kenya, seventh, produced about 5 billion kWh, about 43 percent of its generation, the largest share of any country.

In 2025, U.S. geothermal plants in seven states produced about 16 billion kWh, about 0.4 percent of utility-scale generation, with California accounting for 68.6 percent of the total. The Geysers in Northern California, the largest known dry-steam field in the world, has produced electricity since 1960.

Let's pretend every town uses heat from under the ground.

Some places have hot rocks close to the top. Other places would need to dig much deeper.

Imagine every home, school and greenhouse kept warm by Earth's heat, and power plants running on underground steam. Geothermal plants can run day and night in any weather, so they would never wait for the wind or the Sun.

But hot water and steam hot enough to make electricity are found mainly in certain places, near volcanoes and the edges of Earth's big plates. Elsewhere, people might use the gentler warmth of the ground for heating, or drill much deeper. Engineers are testing new ways to reach hot rock almost anywhere.

Geothermal plants produce electricity consistently and can run essentially around the clock regardless of weather, and can ramp up or down with demand (DOE). That makes them unlike variable sources.

The constraint is geology. Electricity generation needs water or steam at about 300 to 700 °F, and plants are generally built where such reservoirs lie within a mile or two of the surface (EIA), mostly near tectonic plate boundaries. Enhanced geothermal systems aim to create engineered pathways in hot rock elsewhere; DOE's 2022 analysis suggests U.S. capacity could reach 90 gigawatts by 2050 if their costs fall sharply.

Earth's heat is very old. Tiny bits inside rocks keep making new heat.

That heat slowly flows up toward the surface.

The U.S. Department of Energy explains that heat flowing from Earth's interior is constantly topped up by the breakdown of natural radioactive elements in rocks, and will be available for billions of years.

The deeper you go, the hotter the rocks and water. Where hot rock lies close to the surface, rainwater soaks down, gets heated, and can come back up as hot springs or geysers. Geothermal power plants drill into these hot reservoirs and use the steam to spin turbines.

DOE: heat flowing from Earth's interior is continually replenished by the decay of naturally occurring radioactive elements and will remain available for billions of years. EIA notes that most major geothermal resources lie near tectonic plate edges, where most volcanoes are, including the Ring of Fire around the Pacific.

Hydrothermal systems need both heat and water moving through porous or fractured rock. A reservoir is renewable only if it is used sustainably: the Government of Iceland warns that excessive production from a geothermal field can only be maintained for a relatively short time.

Geothermal power plants don't burn fuel.

They let out much less smoky gas than coal or gas power plants.

Geothermal power plants don't burn fuel. The EIA says they release about 99 percent less carbon dioxide and about 97 percent less sulfur gas than power plants that burn fossil fuels. Most also pump the water they use back underground.

There are trade-offs too. Underground water can carry a smelly gas called hydrogen sulfide, which plants clean out with scrubbers. And if too much hot water is taken out too quickly, a field can cool down, so people have to use it carefully.

EIA: geothermal plants emit about 97 percent less sulfur compounds and about 99 percent less carbon dioxide than fossil-fuel plants, use scrubbers to remove hydrogen sulfide naturally present in reservoirs, and mostly reinject used steam and water.

DOE adds that over a 30-year life cycle, geothermal plants use less land than many other sources. Long-term output depends on managing each reservoir: overproduction can only be sustained briefly, which is why reinjection and careful extraction rates matter.