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How do they know that it is solid?)
by lngnmn 10y ago
How do they know that it is solid?)
- Mindstormy 10y agoSeismic waves traveling through the earth refract for the same reason that light refracts when entering different substances (e.g. air, water). The inner core has a different density from the outer core, and this difference in density tells us that it is solid. Of course the density difference could be due to something we don't know yet, but this is out current best guess.
- vkou 10y agoBy measuring how quickly seismic waves travel between different points on the earth's surface. Seismic waves travel at different speeds depending on the density and type of material they pass through, which lets us determine the composition of the Earth.
- deleted 10y ago[deleted]
- q3r3qr3q 10y agoMeasuring earthquake wave propagation?
- jschwartzi 10y agoYes. And to add a missing piece, seismic waves radiate out from the point of vibration. Some of these waves pass through the core of the earth and are received on measurement equipment on the other side. Some of these waves pass through the mantle or the crust. If we know the epicenter of the quake, then we can estimate how long these waves should take to reach our different measuring stations assuming different densities. Given that we can know how long they actually do take, we can turn around and estimate the mean density along the straight-line path they took. When we determine that the mean density is significantly higher for paths through the center of the earth, that tells us that the material there is much denser, and so we suppose that it could be solid.
- nickjarboe 10y agoTo the first order it is the fact that a liquid only propagates pressure waves while a solid can propagate shear and pressure waves (which propagate a different speeds).
- rcthompson 10y agoThat's true, but can shear waves be transmitted to the earth's solid core through the liquid iron surrounding it?
- Florin_Andrei 10y agoPressure waves go through the liquid part, hit the solid part, some of their energy is converted into shear waves which go through the solid core, convert back to pressure waves on the other side, and eventually hit the surface again. By measuring propagation time, direction, etc, the full picture is only compatible with the pressure / shear / pressure double conversion. TLDR: It's complicated.