The ground gets hot deep down.
It is very hot under our feet. This heat stays inside the Earth. We can use this heat for power. It helps us stay warm.
Do you want to feel the heat?
The ground gets hotter as you go deep.
This happens because of heat inside the Earth. This heat comes from many places. Some heat comes from tiny bits of rock. These bits break down and make heat.
Other heat comes from when the Earth was made. The heat flows up toward the surface. We can use this heat for power. It can also keep us warm. The heat is always there for us to find.
The ground gets hotter as you go deeper. This change in heat is called the geothermal gradient.
Near the surface, weather and climate change the temperature. This only affects the top few hundred meters. Below that, heat from inside the Earth takes over. In the crust, heat rises about 25 to 30 degrees Celsius every kilometer.
Where does this heat come from? Much of it comes from radioactive decay. This is when tiny parts of rocks break down and give off heat. This process makes up 45 to 90 percent of the heat escaping Earth. Other heat comes from when the planet was first made. It also comes from the core as it turns into solid metal.
We can use this heat for geothermal energy. People use it to heat homes or make electricity. To make power, we use steam to turn a turbine.
Scientists study this by drilling deep holes. The inner core is very hot. It can reach 7000 Kelvin. The pressure at the center is also very high.
The Earth is not a cold, dead rock. It is full of heat that flows from the inside toward the surface. This change in temperature as you go deeper is called the geothermal gradient.
Near the surface, the temperature is mostly shaped by the weather and the local climate. These changes only reach a shallow depth of a few hundred meters. Below that, the heat from deep inside the planet starts to take over. In the continental crust, the temperature rises about 25 to 30 degrees Celsius for every kilometer you go down.
This heat comes from several different sources working together. A huge amount, between 45 and 90 percent, comes from radioactive decay. This happens when certain elements in the mantle break down and release energy. The main elements doing this work are potassium-40, uranium-238, uranium-235, and thorium-232. Other heat comes from the time when Earth was first formed. It also comes from the liquid outer core turning into solid metal at the inner core boundary.
This constant flow of energy is what keeps the planet active.
Scientists have learned a lot about this heat over time. They know that Earth was much hotter in the past. About 3 billion years ago, the heat production was twice as high as it is today. This high heat caused faster movement in the mantle and different types of rocks to form. Today, researchers use special tools to study these temperatures. They often drill deep holes to measure the heat at the bottom.
This helps them understand how the heat moves through different layers.
There are many amazing numbers to describe the Earth's interior. The inner core can reach temperatures between 4000 and 7000 Kelvin. At the very center, the pressure is about 360 gigapascals. This is a massive amount of pressure, equal to about 3.6 million atmospheres. The total heat content of the Earth is estimated at 10^31 joules. Scientists also measure how much heat escapes the planet. The total heat loss is estimated to be around 44.2 terawatts.
We can use this natural heat to help humans in many ways. This is called geothermal energy. People have used this heat for bathing and heating since the time of the ancient Romans. Today, we can use high temperatures to create electricity. We do this by passing steam through a turbine that is connected to a generator. This provides a very reliable way to make power. As of 2007, about 10 gigawatts of geothermal electricity capacity was installed around the world.
The geothermal gradient is the rate at which temperature increases as you move deeper into the Earth's interior. It is a fundamental concept in geology because it describes how heat moves from the planet's hot center toward the surface. This movement of heat drives many of the processes that shape our world, such as plate tectonics and volcanic activity. While the surface temperature is mostly controlled by the atmosphere, the deep interior is governed by much more powerful energy sources. Understanding this gradient helps scientists model how the Earth functions as a dynamic system.
Heat moves from the core to the surface through several different physical processes. In the lithosphere, which is the Earth's rigid outer shell, heat moves primarily through conduction. Conduction is a process where heat is transferred through direct contact between materials. However, in the mantle below the lithosphere, heat moves mainly through convection. Convection occurs when hot material rises and cooler material sinks, creating a circulating motion. This difference in how heat moves causes the geothermal gradient to be steeper in the lithosphere than in the mantle.
There are several distinct sources that provide the Earth with its internal heat. A massive portion, estimated between 45 and 90 percent, comes from radioactive decay. This happens when unstable elements like potassium-40, uranium-238, uranium-235, and thorium-232 break down. These elements are often concentrated in the continental crust, which acts as a major reservoir for them. Other heat comes from the planet's formation, known as planetary accretion. Additional heat is released during differentiation, when heavy metals like iron and nickel sank to form the core. Finally, latent heat is released as the liquid outer core crystallizes into the solid inner core.
Earth's internal temperature and heat production have changed significantly over billions of years. Scientists believe that early in Earth's history, the planet was much hotter due to a higher concentration of radioactive nuclides. Approximately 3 billion years ago, heat production was about twice what it is today. This higher heat led to larger temperature gradients and faster mantle convection. These intense conditions allowed for the creation of unique igneous rocks called komatiites, which are no longer formed today. This history shows that the geothermal gradient is not a constant value over geological time.
The scale of Earth's internal energy is truly immense. The total heat content of the planet is estimated to be 10^31 joules. The inner core is incredibly hot, with temperatures ranging from 4000 to 7000 Kelvin. At the very center of the planet, the pressure reaches about 360 gigapascals, which is roughly 3.6 million atmospheres. The Earth constantly loses heat to space at an estimated rate of 44.2 terawatts. This heat loss is replenished by radioactive decay at a rate of about 30 terawatts.
Temperature variations can also be seen in the shallow layers near the surface. The top few hundred meters are influenced by local weather, seasons, and even past climate changes. For example, in areas with deep permafrost, a low-temperature anomaly can persist hundreds of meters down. In some regions, scientists use the geothermal gradient to study the history of the land. If a region has experienced uplift or erosion, the shallow gradient will appear higher. Conversely, in areas of subsidence, the initial gradient may appear lower before reaching a stabilized state.
Humans can harness this natural heat through a process called geothermal energy. This is a renewable resource that provides reliable, baseload energy with a reliability rate exceeding 90 percent. In areas with high geothermal energy density, we can generate electricity by using heat to create steam. This steam then passes through a turbine connected to a generator. As of 2007, about 10 gigawatts of geothermal electric capacity was installed worldwide. Additionally, 28 gigawatts of capacity is used for direct heating in industries, spas, and homes.
Where will your curiosity go next?
🖼️ Images & Media (5)
More to explore
✨ What else?
Related topics you might enjoy
🔬 Go deeper
More advanced topics to explore
🪜 Step back
Simpler topics to build understanding
What is Nepedia?
A free, ad-free encyclopedia for children. Every article is written at five reading levels, so the same page works for a five-year-old and a fifteen-year-old — use the level switcher above to see this one change. No account needed to read.