The Hidden Source of Earth's Heat

You’ve heard the earth’s core is made of molten rock and at such high temperatures, it can melt rocks as hard as granite. But you may be wondering how does the earth keep producing heat at such a temperature that it can melt rocks? This article will explain how radioactive minerals inside the earth keep producing heat that makes the core hot enough to melt rocks despite its distance from the sun and lack of convection currents caused by no water mantle layer surrounding it. When it comes to any science-related topic, the temperature for melting rocks is one of the most interesting topics to know more about. The earth has been producing heat and pressure over millions of years and this pressure has led to the formation of rocks. 

Eruption of the Kilauea volcano

The Earth’s core is mostly composed of iron and nickel, and the outer core has temperatures of about 5,400 degrees Fahrenheit (3,000 degrees Celsius). It is kept molten by heat from decaying radioactive minerals in the upper part of the mantle that rises to the outer core, transferring heat to the liquid metal. As this heat causes portions of the core to become lighter and less dense than their surroundings, it causes them to rise; this rising creates convection currents that help maintain plate tectonics and power Earth’s magnetic field.

layers of the earth

Sources of  Earth's Thermal Energy.

Radioactive  Minerals

Given the effects of radioactive minerals on temperature changes and the melting of rocks, how do these minerals contribute to the melting of rocks around the earth's core? For this answer, please note that radioactive decay is a process in which an unstable atomic nucleus loses energy by emitting radiation. Thanks to radioactivity, a natural form of heat always persists on the earth's surface and in its crust. All radioactive elements eventually decay into new ones.

 There are many different types of naturally-occurring radioactive isotopes, including carbon-14, uranium-238, and more. potassium-40; thorium-232; radium-226 the disintegration of rubidium-87 and strontium 90. means that any specimen of radioactive mineral or rock will have small amounts of atoms in it that are no longer part of their original element. Once these atoms break free from their original elements, they look for another partner to bond with-a the bond they need or they'll quickly become unstable. Heat in the Earth's interior is mostly generated by the decay of radioactive elements, which are found in small amounts in all rocks. The heat is transferred to the surface by conduction and convection within geological materials. Radioactive materials not only generate heat but also generate electric currents, which are responsible for producing the magnetic field that surrounds the earth.

Uraninite Uranium Oxide Mineral Ore

Earth Core 

The earth has an outer core and an inner core. The inner core is a solid ball of iron and nickel that is surrounded by a liquid outer core. The inner core is so hot that its surrounding liquid outer core is in a state of constant boiling. This boiling outer core spins and moves the rest of the planet's mantle around like a slow-moving conveyor belt. The movement of the outer core causes friction between the mantle and the crust which creates heat and results in magma being produced. The heat inside the earth melts rocks because some radioactive minerals or rocks decay or break down over hundreds of millions of years into other elements or minerals that release energy as heat to their surroundings.

Dynamo Theory - Outer core convection and magnetic field generation

Plate Tectonics 

As tectonic plates shift, they crash into each other and, in a way, push against each other. There is a lot of friction involved as the plates meet one another. In this process, a lot of heat is produced at the juncture between these two even though some of this heat leaves space through volcanoes and other vents in the crust, it is quickly replaced by new heat produced by subduction. When two plates collide and one plate subducts beneath another plate, friction between colliding plates generates heat that can raise temperatures to over 1100 degrees Celsius at depths greater than 100 kilometers below the surface.

plate tectonics

Primordial Heat

The residual heat left over from the formation is known as primordial heat. This is different from radioactive decay in that it does not add energy to the planet's system in any way it merely represents leftover energy from when the planet was assembled during its accretion stage (when dust particles collided with each other and stuck together to form larger particles).

Planets in the Making.

Primordial heat comes from four places:

1. Impact energy (from all the meteors that have hit Earth since its formation)

2. Friction from accretion (the process by which objects collide together to form larger objects like planets)

3. Gravitational release (the release of gravitational potential energy as matter falls into the forming planet)

4. Decompression heating (the release of heat resulting from compression during accretion)

Geothermal gradient

Geothermal gradient is the rate at which the temperature increases with depth in the Earth's crust. Near the surface, it averages about 25 °C/km (72 °F/mi) of depth (geothermal gradient = 25 C° per km deep). In areas where hot magma intrudes into cooler rock, the geothermal gradient can be much higher. The magma that created these regions was produced at depth because the geothermal gradient temperature increases with depth inside the earth causing partial melting of rock in the mantle or crust. This is also why earthquakes occur on or near plate boundaries; as plates move past each other they cause pressure on a rock beneath them leading to earthquakes. The rate at which it increases ("geothermal gradient") varies by location. In general, geothermal gradients are higher where volcanoes are present because volcanoes are evidence of recent (geologically speaking) magma beneath that spot.

Tectonic evolution of Earth


The Earth’s internal geothermal heat flow is the product of both radioactive decay in the Earth’s crust and mantle, and of primordial heat leftover from the formation of the Earth. Radioactive decay today provides about 60% of the total heat, with a further contribution coming from primordial heat. Together these sources account for all the geothermal heat flow that makes its way to the surface in volcanic areas and drives plate tectonics and other geological phenomena like vulcanism, mountain building, and ocean trenches. 

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