How Do We Know How Hot the Core of the Earth Is?

At the Earth’s core, the pressure is about 9 million times the atmospheric pressure. This makes it absolutely impossible to access. The furthest we have dug a hole on Earth is just 9 miles, which barely scratches the surface. However scientists say the temperature down there is about 10,800º F (same as the surface of the sun). How did they arrive at this number?
These are the top answers from the internet to our question.

1.

One of the main ways we’ve learned about the earth’s interior is by studying Earthquakes.
Scientists have learned a lot about how vibrations (which is what Earthquakes are) travel through different types of materials (solids, liquids, semi-solids.)

Imagine you take a big rock and put your hands on the side of it, while somebody else taps it with a hammer, you’d sense different things if the person tapped right next to your hands, or if they tapped further away, or if they tapped on the far side of the rock. If your hands were really sensitive, and you kept a detail of what you felt, you’d learn a lot about that. Then imagine doing the same thing with different materials, maybe a big jello mold, or an inflated basketball, or a bucket of water. You’d pretty soon know what kind of vibrations would feel like from different kinds of taps in different places on different materials.

Scientists have sensors all around the world that measure earthquakes and other vibrations in the earth very precisely. Let’s say a big Earthquake happens in Japan, it will be detected in Japan and the nearby region, but also in America, and Australia and Europe. By comparing the types of vibrations detected in those different parts of the world, and looking at how long they took to travel, scientists can infer quite a lot about the types of material that the vibrations were traveling through.

Then they take information from other scientists who have studied the kinds of stuff the earth is made of, and how those materials behave under heat and pressure. When the different groups of scientists put their data together they are able to form a pretty clear understanding of the composition of the interior of the planet without having to observe it directly.

2.

Short Answer: Math
Long(er) Answer: We don’t actually KNOW with 100% certainty. We learn new things all the time. However using mathematical models we are able to accurately determine some things, like where fault lines and natural resources are.
We are also able to speculate with reasonable assumptions of accuracy on others (like the composition of the center of the earth).

But there are many details that we have to accept as ASSUMPTIONS – reasonable or otherwise. We still can’t predict earthquakes or volcanoes with a comfortable level of “when” and “how bad” accuracy.
The exact mechanics happening underground are still mathematical models that SO FAR have done a good job at accurately explaining what happens AFTER it has happened (like earthquakes). So we keep the existing models until a new one comes along.

3.

There are several slightly complicated mathematical equations, but essentially scientists use them to find the mass of the Earth. Using the vibration of earthquakes, it can be found that the core is made of iron because the vibrations are different when travelling through iron as opposed to aluminum.

Now that we know the mass of the Earth and the size and makeup of the core, we can find how much force the sheer weight of Earth’s gravity is pushing onto the core (from all directions). An iron core will change temperature with more pressure. If your mom ever cooked with a pressure cooker, that is a perfect example of how compressing the air around your food will let more heat into it.

We know the melting temperature of iron, and we also know how much pressure must be applied to iron to make it a liquid (or in Earth’s case, a liquid under so even more pressure so that it seems like a solid again).

Another interesting and simple way to tell if a planet’s core is hot enough to be a liquid is to observe how much the Sun’s gravity pulls the planet into a slightly non-circular (or non-spherical) shape. This is how we know that Mars has at least a partially molten core, because the Sun squishes it like a pancake (very slightly) at certain points in its orbit. If Mars had a solid core, it wouldn’t squish so much.

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