At the Earth's crust, the temperatures remain relatively stable all year round. However, beneath the crust, under our feet is an incredibly hot place — the Earth's core!
From driving plate tectonics to keeping us safe from solar radiation, the Earth's core is not only interesting but also, in part, vital for life on Earth. But, how long can the Earth's core stay hot?
Read on to find out.
How hot is the center of the Earth?
How hot is the core of the Earth?
How did it get so hot in the first place?
One theory is that around 4.5 billion years ago, our Solar System consisted of a cloud of cold dust particles This cloud of gas and dust was somehow disturbed and started to collapse, as gravity pulled everything together, forming a huge spinning disk.
The center of the disk accreted to become the Sun, and the particles in the outer rings turned into large fiery balls of gas and molten-liquid that cooled and condensed to take on solid form.
At the same time, the surface of the newly formed planet was under constant bombardment from large bodies slamming into the planet, producing immense heat in its interior, melting the cosmic dust found there.
When Earth was formed, it was a uniform ball of hot rock. Radioactive decay and leftover heat from the planet's formation caused this ball to become even hotter. Eventually, after about 500 million years, the Earth's temperature reached the melting point of iron—about 1,538° Celsius (2,800° Fahrenheit).
This allowed Earth’s molten, rocky material to move even more rapidly. Relatively buoyant material, such as silicates, water, and even air, stayed close to the planet’s exterior and would become the early mantle and crust. Droplets of iron, nickel, and other heavy metals gravitated to the center of Earth, forming the early core. This process is called planetary differentiation.
Unlike the mineral-rich crust and mantle, the core is thought to be made up almost entirely of metal — specifically, iron and nickel. While the inner core is thought to be a solid ball with a radius of around 760 miles (1,220 km), with a surface temperature of 5,700 K (5,430 °C; 9,800 °F); the outer core is thought to be a fluid layer of about 2,400 km (1,500 miles) thick and reaching temperatures ranging from 3,000 K (2,730 °C; 4,940 °F) to 8,000 K (7,730 °C; 13,940 °F).
The core is thought to be so hot due to the decay of radioactive elements, leftover heat from planetary formation, and heat released as the liquid outer core solidifies near its boundary with the inner core.
So, the core is incredibly hot, but just how much longer can it remain hot?
Scientists at the University of Maryland claim they will be able to answer the question within the next four years.
Driving Earth’s tectonic plate movement and powering its magnetic field requires an immense amount of power. The energy is derived from the center of the Earth, but scientists are certain the core is very, very slowly cooling off.
What makes the center of the Earth hot?
Keeping the center of the Earth hot are two sources of "fuel": primordial energy left over from the formation of the planet and nuclear energy that exists because of natural radioactive decay.
The formation of the Earth came at a time when the solar system was brimming with energy. During its infancy, meteorites constantly bombarded the forming planet, causing excessive amounts of frictional force. At the time, Earth was rife with volcanic activity.
How long will the Earth's core last?
Since the beginning, the planet has cooled significantly. However, residual heat from the formation of Earth remains. Although the primordial heat has largely dissipated, another form of heat continues to warm the mantle and crust of the Earth.
Naturally radioactive materials exist in large quantities deep in the Earth, with some residing around the crust. During the natural decay process of the radioactive material, heat is released.
Scientists know heat flows from Earth's interior into space at a rate of about 44 × 1012 W (TW). What they do not know, however, is how much of the heat is primordial.
The issue is that if the Earth's heat is predominantly primordial, then it will cool off significantly quicker. However, if the heat is created mostly in part due to radioactive decay, then the Earth's heat will likely last much longer.
While that sounds pretty alarming, some estimates for the cooling of Earth's core see it taking tens of billions of years, or as much as 91 billion years. That is a very long time, and in fact, the Sun will likely burn out long before the core — in around 5 billion years.
Why is the Earth's core temperature important?
Earth's core keeps the temperature stable, but more importantly, it keeps the Earth's magnetic field in place. Earth’s magnetic field is created by the motion of the molten metal outer core.
This massive magnetic field extends into space and holds charged particles in place that are mostly collected from the solar winds.
The fields create an impenetrable barrier in space that prevents the fastest, most energetic electrons from reaching Earth. The fields are known as the Van Allen belts, and they are what enables life to thrive on the surface of the Earth. Without the shield of the magnetic field, the solar wind would strip Earth’s atmosphere of the ozone layer that protects life from harmful ultraviolet radiation.
The collection of charged particles deflects and captures the solar wind preventing it from stripping the Earth of its atmosphere. Without it, our planet would be barren and lifeless. It is believed that Mars once had a Van Allen belt that protected it too from the Sun's deadly wind. However, once the core cooled, it lost its shield, and now it remains a desolate wasteland.
How long will the Earth's fuel last?
Currently, many scientific models can estimate how much fuel remains to drive the Earth’s engines. The results, however, greatly differ making a final conclusion difficult to draw. At the moment, it is unknown how much primordial and radioactive energy remains.
“I am one of those scientists who has created a compositional model of the Earth and predicted the amount of fuel inside Earth today,” said one of the study’s authors William McDonough, a professor of geology at the University of Maryland.
“We’re in a field of guesses. At this point in my career, I don’t care if I’m right or wrong, I just want to know the answer.” However, researchers believe with modern technological advancements, a more accurate prediction can be made.
To determine how much nuclear fuel remains in the Earth, the researchers use advanced sensors to detect some of the tiniest subatomic particles known to science—geoneutrinos. Geoneutrino particles are the byproducts generated from nuclear reactions that take place within stars, supernovae, black holes, and human-made nuclear reactors.
Detecting how much fuel is left
Detecting antineutrino particles is an immensely difficult task. Massive detectors the size of a small office building are buried over 0.6 miles (a kilometer) down into the Earth's crust. The depth may seem like overkill; however, it is necessary to create a shield from cosmic rays that can result in false positives.
In operation, the detector can detect antineutrinos when they collide with hydrogen atoms inside the apparatus. After the collision, two bright flashes can be detected, unequivocally announcing the event.
By counting the number of collisions, scientists can determine the number of uranium and thorium atoms that remain inside of our planet.
Unfortunately, the detectors KamLAND in Japan and Borexino in Italy only detect about 16 events per year, making the process painstakingly slow. However, with three new detectors projected to come online in 2020 — the SNO+ detector in Canada and the Jinping and JUNO detectors in China — researchers expect more than 500 more detected events per year.
“Once we collect three years of antineutrino data from all five detectors, we are confident that we will have developed an accurate fuel gauge for the Earth and be able to calculate the amount of remaining fuel inside Earth,” said McDonough.
The Jinping detector in China is over four times bigger than all the detectors to date. Although the detector is big, the JUNO detector will be a staggering 20 times bigger than all existing detectors.
“Knowing exactly how much radioactive power there is in the Earth will tell us about Earth’s consumption rate in the past and its future fuel budget,” explained McDonough.
“By showing how fast the planet has cooled down since its birth, we can estimate how long this fuel will last.”
When JUNO comes online; hopefully in 2021 — the data collected should help scientists like McDonough estimate the time left for the Earth's core to cool. Until then, rest assured, that any estimates made are likely going to run into the hundreds of millions, perhaps billions, of years in the future.
So, there is no need to make plans to move to a new planet anytime soon.