What If Earth's Core Cooled Down?

By: Chris Opfer  | 
 model of Earth's core
This is a model of Earth's core at China's Nanjing Geological Museum. It's probably pretty temperate in this model, but a cooling of the actual core could wreak havoc on the planet's magnetic field. © Sean Yong/Reuters/Corbis

At its core, Earth is a hot rock. Sure, it may not seem that way on a cold, dark morning in the dead of winter, but far below Earth's mostly solid rock surface lies a hot center made almost completely of metal. The earth's liquid outer core is an iron-and-nickel alloy that serves as a buffer between the inner core and Earth's mantle, a layer of magma and molten rock.


How Hot is the Core of the Earth?

The inner core is the Earth's hottest spot, with a temperature as high as 11,000 degrees Fahrenheit (6,093 degrees Celsius). It's a solid, iron-rich ball that scientists measure to be about 750 miles (1,200 kilometers) thick and 1,802 miles (2,900 kilometers) below Earth's surface [sources: National Geographic, Schultz].

With all the talk these days about the harmful effects of global warming and increasingly hot temperatures on Earth, you might assume that Earth's core could stand to chill out a bit. In truth, we need the planet's inner core to remain at a blistering hot temperature so that it can protect Earth from potentially harmful solar winds and debris.


Earth's Four Different Layers, Explained

  • Inner Core: Deep in the heart of Earth's interior, also known as the center of the earth, lies the inner core, a formidable layer that extends approximately 1500 miles (2414 kilometers) deep. Comprised primarily of iron and nickel, both the inner and outer cores sizzle at scorching temperatures ranging from 7200–9000 degrees Fahrenheit (4000–5000 Celsius). Remarkably, the inner core remains solid despite these extreme heat levels, a feat sustained by the immense pressure it endures.
  • Outer Core: Immediately surrounding the inner core is the outer core, encompassing a thickness of about 1300 miles (2092 kilometers). Like its inner counterpart, the outer core is predominantly composed of iron and nickel, and it simmers at temperatures ranging from 7200 to 9000 Fahrenheit (4000–500 Celsius). Unlike the solid inner core, the outer core is in a liquid state, known as the liquid outer core, responsible for generating the Earth's magnetic field.
  • Mantle: Dominating Earth's volume, the mostly solid mantle forms an extensive layer about 1800 miles (2880 kilometers) thick. It's where the liquid outer core solidifies. Composed of dense, dark rock, the mantle exhibits a progressive increase in temperature as one delves deeper within the Earth. Near the chilly outer crust, the temperature hovers around 1300 degrees Fahrenheit (700 Celsius), while deeper regions adjacent to Earth's core heat up to a blistering temperature of 7200 degrees Fahrenheit (4000 Celsius).
  • Crust: Earth's outermost layer comprises two distinct types: continental and oceanic crust. Continental crust, rich in silica, is an average of 44 miles (70 kilometers) thick. In contrast, oceanic crust predominantly consists of silica-poor rocks like basalt, making it thinner and more flexible at a mere 3 miles (5 kilometers) in thickness. These distinct crusts contribute to the Earth's diverse geological features and characteristics [Source: California Academy of Sciences].

The Origin of the Earth's Core

The temperature of the Earth's core is about as toasty as the sun's surface. It's been that way since, oh, about 4.5 billion years ago. That's when the planet first formed from a cloud of gases and particles. Gravity caused iron and other heavy substances to sink deep into the middle of Earth, while lighter material like air and water rose past the Earth's mantle to the crust. The stuff in the middle is so hefty that the outer core's gravity is about three times that of Earth's surface.

It still maintains some of its original heat, as well as that created by gravitational friction from the movement of heavier materials closer to the center. The inner core continues to grow by about a centimeter every thousand years, gaining more heat as it expands. Decaying radioactive isotopes also add heat to the mix as they radiate from the Earth's mantle [source: Anuta].



What Happens If The Earth's Core Cools Down?

If the core were to cool completely, scientists believe the planet would grow cold and dead. It also would get a little dark: Power utilities pull radiant heat from Earth's crust and use it to heat water, the steam from which powers turbines to create electricity [source: Anuta].

Magnetic Shield

Cooling also could cost us the magnetic shield around the planet created by heat from the core. This shield protects Earth from cosmic radiation. It's created by a convection process caused by constantly moving iron.


Like the planet itself, Earth's core is constantly spinning – some scientists think it's moving even faster than the rest of the planet. The friction converts kinetic energy into electrical and magnetic energy that forms the field, which deflects harmful, charged particles emanating from the sun toward the north and south poles [sources: Folger, USGS].

Earth Without a Magnetic Field

Just how much losing the magnetic field would change life on Earth isn't clear. Some scientists say the planet could see an onslaught of radioactive waves that would overheat the planet and make it uninhabitable. Other scientists point to a possible uptick in solar rays that are believed to cause cancer.

Still more observers say we could experience sweeping solar winds, perhaps as strong as those that may have swept all of the oceans, lakes and rivers from Mars and Venus. It's safe to say we're better off not finding out exactly what losing the magnetic field would mean [source: Schirber].


Size Plays a Role

Why Hasn't It Happened Yet?

Imagine a scenario where Earth's core cooled down, plunging our planet into an entirely different reality. To understand why this hasn't happened, we need to consider Earth's size.

Without the electric dynamo of the molten outer core, our protective magnetic shield would fade to zero. This would pave the way for the relentless solar wind, a stream of charged particles from the Sun, to start stripping away our atmosphere, much like what might have occurred on Mars in the distant past.


For Earth to have already cooled to this extent, it would need to be considerably smaller. The gravitational forces generated by a planet's compression and the friction it endures will naturally heat it up, keeping the core at its molten hot temperature. Additionally, the decay of radioactive elements within the mantle continues to contribute to this heat [Source: BBC].

What Happened to the Moon?

To illustrate this, consider the Moon. Scientists believe the moon formed as a result of a colossal collision in our solar system between an early Earth and a Mars-sized body called Theia. This occurred roughly 4.5 billion years ago. Despite initially sharing a molten state due to the energy of this impact, the Moon cooled down much faster than Earth because of its smaller size [Source: NASA].

What a Smaller, Colder Earth Would Look Like

A smaller, cold Earth, however, would have lacked essential geological features like volcanoes and plate tectonics, which have played a crucial role in recycling carbon and minerals within the Earth's crust, while simultaneously adding vital gases to the atmosphere. Today, volcanic activity is our Earth's main cooling mechanism [Source: Carleton Newsroom].

Without a thick atmosphere, the temperature of our Earth's surface would plummet, leading to the freezing of the planet's oceans. In such frigid conditions, the evolution of complex life, as we know it, would be highly improbable. This means that our Earth's core actually protects life on our planet [Source: BBC].


Earth’s Core FAQs

What if Earth's core cooled down?
Earth has a very hot molten iron core. If it cooled down, scientists believe the planet would grow cold and dead. Cooling also could cost us the magnetic shield around the planet created by heat from the core. This shield protects Earth from cosmic radiation.
How deep is Earth’s core?
The Earth's interior core is about 1,802 miles deep. It has a radius that spans over 2,165 miles.
How long will it take for Earth's core to cool?
If the sun died and Earth managed to survive, scientists believe the iron core would take about 91 billion years to turn completely solid. Furthermore, Earth will take billions of years more to cool down to the temperature of outer space due to a large amount of heat dissipation from the planet.
How hot is Earth's core?
Earth’s inner core exudes heat at such high temperatures that it goes beyond the melting point of iron. Scientists measure the temperature of the Earth's inner core to be as hot as 9,392 degrees F.
What keeps Earth's core hot?
The heat created at the time Earth formed hasn’t been lost yet. Other factors include frictional heat caused by the sinking of the denser material to the core and heat generated from decayed radioactive elements.

Lots More Information

Related Articles

  • Anuta, Joe. "Probing Question: What heats the earth's core?" Phys.org. March 30, 2006 (May 17, 2015) http://phys.org/news/2006-03-probing-earth-core.html
  • California Academy of Sciences. "From Core to Crust: Defining Earth's Layers." https://www.calacademy.org/explore-science/from-core-to-crust-defining-earths-layers
  • Folger, Tim. "Journeys to the Center of the Earth." Discover Magazine. July 14, 2014 (May 17, 2015) https://www.discovermagazine.com/planet-earth/journeys-to-the-center-of-the-earth
  • National Geographic. "Core." (May 17, 2015) https://www.nationalgeographic.org/encyclopedia/core/
  • Rizo, Hanika, et al. "Earth's Core Has Been Leaking for Billions of Years." Carleton Newsroom. (July 9, 2019). https://newsroom.carleton.ca/story/earths-core-leaking/
  • Schirber, Michael. "How Vital Is a Planet's Magnetic Field? New Debate Rises." Space.com. March 21, 2011 (May 17, 2015) http://www.space.com/11187-earth-magnetic-field-solar-wind.html
  • Schultz, Colin. "The Center of the Earth is as Hot as the Sun." Smithsonian Magazine. April 26, 2013 (May 17, 2015) http://www.smithsonianmag.com/smart-news/the-center-of-the-earth-is-as-hot-as-the-sun-43631207/?no-ist
  • Tavares, Frank. "Collision May Have Formed the Moon in Mere Hours, Simulation Reveal." NASA. (October 4, 2022) https://www.nasa.gov/solar-system/collision-may-have-formed-the-moon-in-mere-hours-simulations-reveal/
  • U.S. Geological Survey (USGS). "How does the Earth's core generate a magnetic field?" May 6, 2015 (May 17, 2015) https://www.usgs.gov/faqs/how-does-earths-core-generate-a-magnetic-field?qt-news_science_products=0#qt-news_science_products
  • Villazon, Luis. "How Earth's Cooling Molten Core Could Destroy the Planet." BBC Science Focus. (March 13, 2023). https://www.sciencefocus.com/planet-earth/earths-molten-core-is-cooling