Given it’s roughly 4,000 miles to the center of the corner, and according to resources, we’ve (humans) have only gotten about 18 miles deep. So how is it possible we know what’s beneath us?
In: 5
We can tell what’s inside by listening to seismic waves – massive sound-like waves produced by earthquakes – in a manner similar to how medical sonography is used to “see” what’s inside a human’s body without cutting it open. We also get a glimpse of the contents of the Earth when it gets ejected outside through volcanoes as lava.
A big part of this comes from measuring earthquakes.
When you get an earthquake there are two main types of waves generated – compression waves (same deal as sound waves) and transverse waves (the material moves side to side – like you’re moving a stretched slinky left and right and sending waves down it).
Both of these can go through solid material, but only the compression waves can go through liquid. Note – water waves you see *look* like transverse waves but they’re a third category where the particles move in a circle, this type of wave can go through liquids.
When an earthquake happens we can measure the seismic readings all over the earth. When looking at these measurements though people noticed that both the the transverse waves and compression waves didn’t turn up everywhere.
Once you get a certain way around the world from the earthquake site the transverse waves disappear even though the compression waves still show up.
This tells us that at some point the solid mantle turns into a liquid phase for the core.
Next up – when waves travel across a change in phase (Eg solid to liquid) they can have their direction changed, called refraction. This is important because the compression waves that do turn up on the other side of the earth from the earthquake also don’t turn up quite where you’d expect them to, and there are some areas they don’t turn up at all.
The result of this is that the waves behave as though at some depth the core changes back from liquid to solid.
[Graphic indicating this process](https://www.cyberphysics.co.uk/MobileVersion/graphics/diagrams/Earth/pand%20s%20shadow.png)
Most things we still dont know, we just have a rough idea about the density and what it is prooobably made of. But we know very little about it. Even things we may have learned in school about this topic, a lot can be just wrong. Science still doesnt know everything and we can sometimes just guess when we dont have a lot of data.
Wouldnt be the first time we had a lot of mistakes in our books. We still have those mistakes, that is sure!
There are many surprises all the time which no scientist couldnt even think of which can lead to wrong conclusions.
We are very early here. We just have a rough idea about the earths core and lots of theories and ideas can be wrong.
Mainly from seismic waves, but it’s just a very very likely guess, we could be *completely* wrong and inside of earth theres a portal that takes us to another dimension
Although obviously that’s very *unlikely*
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