# How does scientists know earth has a solid core surrounded by mantle when we have never dug so deep? How do that happens when IMO 12 km is the deepest we have dug?

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How does scientists know earth has a solid core surrounded by mantle when we have never dug so deep? How do that happens when IMO 12 km is the deepest we have dug?

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We know that because we send sound waves down into the ground.

Sound waves move faster when they pass through solid material.

So measuring how those waves change as they move through the earth tells us what kind of material they have travelled through.

They did calculations on the speed of sound in various material phases of the most probable matter at given locations, and study the waves from earthquakes and how they propagate through the different media, and noticed waves bounce off of a phase contrast boundary layer.

Earthquakes create waves which travel through the Earth and they can measure how long it takes to pass through certain parts. https://youtu.be/Oum1JnrI0XY

Scientists have used seismic waves to determine the composition of the Earth’s interior. Seismic waves are like sound waves, but they travel through the Earth instead of through the air. When an earthquake occurs, seismic waves travel through the Earth and bounce off boundaries between different layers. By measuring the time it takes for the waves to travel to different points on the Earth’s surface, scientists can determine the size and composition of the Earth’s core, mantle, and crust. Because seismic waves travel faster through solid material than through liquid material, scientists can determine that the Earth’s core is solid and the mantle is liquid.

Just echoing that scientists use earthquakes to determine the earth’s structure. Waves travel through different materials at certain speeds. Additionally, there are two kinds of earthquake waves, one of which does not travel through the earth’s core.