Earth’s interior reaches temperatures of several thousand degrees, with the deepest regions approaching the heat at the surface of the Sun. Temperatures generally increase with depth, rising from the relatively cool rocks of the crust to the intensely hot metallic core. Near the center of the planet, temperatures are estimated to reach about 5,000 to 6,000 degrees Celsius (9,000 to 10,800 degrees Fahrenheit).
This heat is not distributed evenly, and the path from the surface to the center involves more than simply getting hotter. Earth’s interior contains distinct layers with different compositions, pressures, and physical properties. Understanding their temperatures helps explain why volcanoes erupt, continents move, Earth’s magnetic field exists, and the planet remains geologically active billions of years after its formation.
Scientists cannot directly measure temperatures throughout Earth’s interior. Instead, they combine observations from earthquakes, laboratory experiments, measurements of heat flowing from the ground, and physical models of how rocks and metals behave under extreme pressure. Together, these methods provide a detailed picture of a world that remains largely inaccessible to direct observation.
How Earth’s temperature changes with depth
Earth has four major structural layers: the crust, the mantle, the outer core, and the inner core. Each occupies a different depth range and has distinctive physical characteristics.
The crust is the thin, rocky shell on which people live. Beneath it lies the mantle, a thick layer of hot rock that extends to a depth of about 2,900 kilometers (1,800 miles). Below the mantle is the metallic core, divided into a liquid outer core and a solid inner core. The inner core begins approximately 5,150 kilometers (3,200 miles) below the surface, with Earth’s center at a depth of about 6,371 kilometers (3,959 miles).
Temperatures generally increase toward the center, but they do not rise at a uniform rate. Near the surface, temperature can increase relatively quickly with depth. Deeper inside the planet, the rate of increase changes because pressure, material properties, and the movement of heat all influence the temperature profile.
Scientists describe the change in temperature with depth as the geothermal gradient. In the upper crust, this gradient commonly averages around 25 to 30 degrees Celsius per kilometer, although actual values vary substantially from one location to another. Near active volcanoes, in regions with hot groundwater, or in areas with unusual geological conditions, the gradient may be much higher. In other places, it can be lower.
The crustal gradient cannot be extended unchanged all the way to the center. If it were, the calculated temperature would be far too high. Heat travels differently through deeper rock, and convection—the movement of hot material that transfers heat as it rises and cooler material sinks—plays a major role in the mantle and outer core.
The crust: From surface temperatures to hundreds of degrees
Earth’s crust varies in thickness. Oceanic crust is generally about 5 to 10 kilometers (3 to 6 miles) thick, while continental crust commonly ranges from about 30 to 70 kilometers (19 to 43 miles). Its temperature depends on depth, local geology, groundwater circulation, and the amount of heat entering from below.
At the surface, temperatures are controlled mainly by sunlight, weather, climate, and seasonal changes. A few kilometers underground, those influences diminish, and the temperature increasingly reflects heat rising from Earth’s interior.
In many continental regions, temperatures at several kilometers of depth can reach roughly 100 to 200 degrees Celsius (212 to 392 degrees Fahrenheit), though local conditions vary. In geothermal areas, temperatures can become much higher over shorter distances. These differences explain why some places are suitable for geothermal energy production while others are not.
The deepest boreholes drilled by humans reach only about 12 kilometers (7.5 miles), far short of the mantle beneath most continents. Even at these depths, drilling encounters difficult conditions involving high temperatures, pressure, and the mechanical behavior of rock.
The crust itself is not a major reservoir of Earth’s total internal heat. It is a relatively thin outer layer through which some of that heat escapes into the atmosphere and oceans. Much of the energy responsible for long-term geological activity originates deeper within the planet.
The mantle: Hot rock that can flow
The mantle extends from the base of the crust to a depth of approximately 2,900 kilometers. It accounts for most of Earth’s volume and consists primarily of solid silicate rocks rich in magnesium and iron.
Mantle temperatures vary with depth and location. Near the upper mantle, temperatures may range from several hundred degrees Celsius to around 1,300 degrees Celsius (2,400 degrees Fahrenheit), depending on the geological setting. Toward the base of the mantle, temperatures are estimated to reach roughly 3,000 to 4,000 degrees Celsius (5,400 to 7,200 degrees Fahrenheit).
Despite these extreme temperatures, most of the mantle is solid. This may seem surprising because familiar rocks melt at much lower temperatures under ordinary surface conditions. Deep inside Earth, however, pressure is enormous. Increasing pressure generally raises the melting temperature of mantle rock, allowing much of it to remain solid even when it is intensely hot.
Solid does not mean rigid forever. Over long periods, mantle rock can deform and flow slowly, much as a very viscous material would. This movement is known as mantle convection. Hotter, less dense material tends to rise, while cooler, denser material tends to sink. The process transfers heat from Earth’s interior toward its surface.
Mantle convection helps drive plate tectonics, the movement of Earth’s large, rigid outer plates. As plates separate, collide, or slide past one another, they reshape ocean basins, build mountain ranges, and contribute to earthquakes and volcanic activity.
Magma forms when some rock melts, rather than because the entire mantle is liquid. Partial melting can occur when hot mantle rock rises and experiences a decrease in pressure, when water lowers the melting temperature of rock, or when temperatures become high enough for melting under local conditions. The resulting magma may rise through the crust and feed volcanoes.
The mantle’s heat therefore has an important influence on the surface, but the relationship is indirect. The slow movement of solid rock, the formation of localized melt, and the transfer of heat through the crust together produce much of Earth’s long-term geological activity.
The outer core: A liquid ocean of metal
Beneath the mantle lies the outer core, which extends from about 2,900 to 5,150 kilometers (1,800 to 3,200 miles) below Earth’s surface. It consists mainly of iron and nickel, along with smaller amounts of lighter elements.
Temperatures in the outer core are estimated to range from roughly 4,000 degrees Celsius (7,200 degrees Fahrenheit) near its upper boundary to around 5,500 degrees Celsius (9,900 degrees Fahrenheit) near the inner core. These values are estimates rather than direct measurements, and the precise temperature profile remains an area of scientific investigation.
The outer core is liquid because the temperature is high enough to melt its iron-rich material at the prevailing pressures. Its behavior differs fundamentally from that of the mantle. Rather than creeping through the material as a slowly deforming solid, liquid metal can circulate more readily.
This circulation plays a central role in generating Earth’s magnetic field. Heat escaping from the core, together with compositional changes as the inner core grows, drives movement in the electrically conducting liquid metal. Earth’s rotation organizes these flows into patterns that sustain the geodynamo, the process that generates the planet’s magnetic field.
The magnetic field extends into space and helps deflect many charged particles from the solar wind. It does not eliminate all radiation or prevent every atmospheric loss, but it is an important part of Earth’s space environment.
The outer core also helps explain why seismic waves behave differently as they pass through the planet. Shear waves, which require a material to resist sideways deformation, cannot travel through a liquid. Their absence through the outer core, combined with the bending and slowing of other seismic waves, provides strong evidence that this layer is liquid.
The inner core: Solid metal at extreme temperatures
At Earth’s center lies the inner core, a sphere of solid iron-rich metal with a radius of about 1,220 kilometers (760 miles). Its temperature is estimated to be approximately 5,000 to 6,000 degrees Celsius (9,000 to 10,800 degrees Fahrenheit).
That range overlaps the approximate surface temperature of the Sun, which is about 5,500 degrees Celsius (9,900 degrees Fahrenheit). The comparison is striking, but the two environments are very different. The Sun’s visible surface is hot plasma, while Earth’s inner core consists primarily of solid metal under enormous pressure.
Why is the inner core solid if it is so hot? The answer is pressure. At Earth’s center, the weight of the overlying planet produces pressures millions of times greater than atmospheric pressure at sea level. This pressure raises the temperature at which iron-rich material melts.
Consequently, the inner core remains solid even though it is hotter than much of the liquid outer core. The distinction illustrates a fundamental principle: whether a substance is solid or liquid depends not only on temperature but also on pressure and composition.
Scientists infer inner-core conditions by studying seismic waves, conducting experiments on iron and iron alloys at extreme pressures, and applying physical models. Laboratory techniques can compress tiny samples to pressures comparable to those deep inside Earth and examine how their properties change. Such experiments are challenging, and translating laboratory results into conditions inside the planet introduces uncertainties.
The inner core is also not perfectly uniform. Seismic observations suggest that its structure and the behavior of waves passing through it vary with direction and location. Researchers continue to investigate its internal structure and evolution, but its solid nature and extremely high temperature are well established.
Where Earth’s internal heat comes from
Earth’s interior is hot partly because the planet formed through violent, energetic processes and partly because it has retained heat over billions of years. Two major sources sustain this internal energy: leftover heat from Earth’s formation and heat generated by radioactive decay.
When Earth formed about 4.5 billion years ago, smaller rocky bodies collided and combined to build a larger planet. These impacts converted kinetic energy into heat. As Earth grew, gravity compressed its material, releasing additional energy. Dense metals, especially iron, sank toward the center during a process called differentiation, releasing gravitational energy and contributing to the heating of the deep interior.
Some of this primordial heat remains today because Earth is large and loses heat relatively slowly. Rock is a poor conductor of heat compared with many metals, and heat must travel through thousands of kilometers of material before escaping. Convection accelerates heat transfer in parts of the interior, but the planet still cools gradually over geological time.
Radioactive decay provides another important source. Naturally occurring isotopes of uranium, thorium, and potassium release energy as they decay into other elements. These isotopes are concentrated primarily in Earth’s rocky layers rather than its metallic core, contributing to the heat generated in the crust and mantle.
The relative contributions of primordial heat and radioactive heating are not known with complete precision. Their proportions depend on estimates of Earth’s total heat loss, the abundance of radioactive elements, and the planet’s thermal history. Nevertheless, both sources are essential to explaining why Earth remains internally hot.
The inner core adds another source of energy to the system as it gradually grows. As iron-rich material crystallizes onto the solid inner core, latent heat is released. In addition, lighter elements are excluded from the growing solid and enter the liquid outer core, helping drive compositional convection. These processes contribute to sustaining the geodynamo.
How scientists estimate temperatures deep inside Earth
Directly measuring temperatures thousands of kilometers underground is impossible with current technology. Scientists instead assemble evidence from several independent methods, each of which reveals part of the picture.
One major source is seismology, the study of waves generated by earthquakes. These waves travel through Earth at speeds determined by the properties of the materials they encounter. Their paths, speeds, and reflections reveal boundaries between layers and provide information about whether material is solid or liquid. Seismic observations do not directly give temperature, but they constrain the structure and physical properties that temperature models must explain.
Laboratory experiments provide another important line of evidence. Researchers heat and compress minerals and metals to reproduce conditions deep within Earth. They measure how materials melt, change structure, and transmit seismic waves under these conditions. Because reproducing the full range of pressure and temperature is difficult, scientists use several experimental techniques and compare the results with observations.
Measurements of Earth’s surface heat flow also help. Heat escapes from the interior through the crust and into the oceans and atmosphere. By measuring this flow across different regions, scientists can estimate how much energy Earth loses and test models of its internal thermal structure.
Computer models bring these observations together. They simulate how heat moves through the mantle and core, how the planet cools over time, and how materials behave under extreme pressure. The most credible temperature estimates are those that remain consistent with multiple kinds of evidence.
Uncertainty increases where direct observations are scarce, particularly near the core. The exact temperatures depend on the properties of iron-rich alloys, the melting behavior of deep materials, and assumptions about how Earth’s interior has evolved. Scientists therefore often report ranges rather than a single definitive number.
Why the hottest parts of Earth do not melt the entire planet
Earth’s interior is not a uniformly molten mass. Temperature, pressure, and composition determine whether each region is solid, liquid, or capable of slow deformation.
The crust is solid because its temperatures are generally below the melting points of its constituent rocks. The mantle is predominantly solid because pressure keeps much of its material below its melting threshold, even at high temperatures. The outer core is liquid because its iron-rich material is hot enough to remain molten under the conditions there. The inner core is solid because pressure raises the melting point of its metallic material above its actual temperature.
These differences also show why there is no single temperature at which every rock or metal melts. Different substances melt at different temperatures, and the melting point of a given material can change substantially with pressure. Minerals containing water or other volatile substances may begin melting under conditions that would leave dry rock solid.
Even within a single layer, temperature can vary. Mantle plumes, subduction zones, and regions near mid-ocean ridges have different thermal conditions. The core also has a temperature gradient, with heat moving outward through its boundaries.
Earth’s interior is therefore best understood as a set of interacting layers governed by pressure, heat transfer, and material properties rather than as a simple sequence of increasingly hot zones.
What Earth’s internal heat means for life and the planet’s future
Earth’s internal heat helps maintain the geological processes that shape the planet. Through mantle convection and plate tectonics, it contributes to the formation and destruction of oceanic crust, the growth of mountain ranges, and the recycling of carbon between the surface and the deep Earth.
Volcanic activity releases heat and gases from the interior, while hot water circulating through rocks can dissolve and transport minerals. These hydrothermal systems support distinctive ecosystems in places such as deep-ocean vents, where organisms obtain energy from chemical reactions rather than sunlight.
Internal heat also makes geothermal energy possible. In suitable locations, wells can bring hot water or steam to the surface for electricity generation or direct heating. The usefulness of a geothermal resource depends on more than temperature alone: rock permeability, water availability, drilling costs, and the rate at which heat can be extracted all matter.
Earth will continue to lose internal heat, although the process is extremely slow on human timescales. As the mantle cools, the planet’s internal dynamics may gradually change. The inner core will continue to evolve as the core loses heat, and the magnetic field will depend on the conditions that sustain liquid-metal circulation in the outer core.
The timing and details of these changes are uncertain because they depend on complex processes unfolding over millions to billions of years. What is clear is that Earth’s interior is not static. It is a slowly evolving system whose remaining heat influences the surface, the magnetic field, and the long-term habitability of the planet.
From the crust to the center, Earth’s temperature rises from conditions shaped by the environment at the surface to thousands of degrees deep underground. The mantle remains mostly solid yet slowly flows, the outer core churns as liquid metal, and the inner core stays solid under extraordinary pressure. Together, these layers reveal how a planet can retain immense heat long after its formation—and how that hidden energy continues to shape the world above.