How do scientists know what the core of the Earth is made of, even though we’ve never drilled anywhere near that deep?
In: Planetary Science
Earthquakes and other seismic events echo and refract through the layers of material inside the Earth. By comparing data from multiple seismographs, some close to the epicenter and some far away, and doing some fancy math, you can build up a rough idea about what the different layers inside the Earth are made of.
By analyzing seismic data and electromagnetic fields. These are, of course, our best *predictions* on its material. We don’t have any direct samples that we’ve drilled out. But we have a lot of data, and know a lot about iron, to predict/know the core is made up of mostly iron.
When you flick an empty cup, it makes a different sound than when you flick a cup full of water.
This is the basic principle of how we know the make up of things that we can’t see. You’ve experienced enough empty cups and full cups to know the sound w/o looking at the cup.
So basically, we have a bunch of data on what’s going on under our feet. Some of it is for things you can see, and some of it for things you cannot see.
However, we can look at the ones we can see and say “pretty consistently, our tools read XYZ measurements when vibrations travel through THIS material, and read ABC measurements when traveling through THAT material, and looking at this data from stuff we can’t see, we see some amount of XYZ before it turns into ABC, so we’ll estimate that there’s some amount of THIS and then there’s some amount of THAT.”
It’s also worth mentioning that this is a similar extrapolation to how we estimate the make up of celestial bodies. Like we can tell if a planet is rocky or not from a different star system? How??
It’s because for the bodies that we DO know the make up for (i.e. the ones closest to us), we see the kind of signatures they put off. Mars and Jupiter have drastically different data when we use all of the instruments we have to measure them, and if we look at a planet light years away we can say “hmm, that one reacts more like Jupiter to our instruments than it does like Mars”.
One of the main ways we can predict whats down there is because vibrations move at different speeds, or not at all, through different materials or different temperatures. We have seismic instruments all over the world that pick up vibrations from earthquakes, and determine what they are passing through based on what they pick up.
Combine that with general assumptions based on what elements we commonly find in the crust and what is contained in magma when it surfaces and you get a rough understanding of what the interior is likely made of.
There is of course, plenty of room for error and further learning. Though it seems really wild at a glance, we only have the most crude and surface-level understanding of the earth’s interior, if we were able to actually drill or observe down there we almost certainly would be learning a lot more. One major example, the LLSVP Zones. Seismic data reveals the existence of two gigantic areas right near the core that are very different from the surrounding mantle, but we don’t really know what they are or why they are there.
In addition to what everyone else has said here, they really don’t. They have some damn good hints as to what is probably down there, but nobody has any way to know for sure. I’m sure the picture will continue to evolve over time.
To add on to what others have said about seismic, we know the rough overall density of the earth due to it’s gravitational pull and size. This means we have to have certain materials inside that can get us to the densities observed.
We can also study asteroids and comets to see their makeup. Especially by studying such interstellar material that comes from the time of the formation of the earth, we can get an idea of what materials were abundant at the time of forming the earth.
Finally, we have super strong presses in laboratories that can take surface materials and transform them to states of matter that only exist under the extreme temperatures and pressure found inside a planet.
Big earthquakes create what’s basically a massive sonar shock.
Scientists have placed sensors all around the place, and by listening in to these vibrations and applying a lot of math they can figure out where the earthquake originated, how the shockwaves bounced afterwards (shockwaves tend to partially bounce when material density changes) and how dense the materials were that the shockwaves transmitted through.
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