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.
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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.
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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].
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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].
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.
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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].
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].
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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.
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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].
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].
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].
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