how do we know that the structure of the earth exists?

Question

the earth has a crust mantle and core. We have never dug below the crust,so how do we know? tell me how scientists have investigated the structure of the earth. Tell me if you know!!!!!! and serious answers

Answer 1

They can tell from earthquake seismic activity sensors. As the quakes waves are going through the earth, they bend and distort at any levels, and reveal much about the internal structure. These readings can be interpreted to produce models of the inner structure, and need to be correlated with the geological theories about the Earth's formation.

Answer 2

Well we can reasonably say that there is the mantle because all the lava and magma that comes from volcanoes and cracks in the crust on the ocean floor has to come from some place. Also we can calculate from the pressure that it comes out of the breaks in the crust , what pressure it is on the very inside edge of the crust and thus the outside edge of the mantle.

As for the core, that is a bit more of a "it follows that...." because when you compress a semi-solid liquid (IE one with extremely low viscosity) unlike most liquids which would spread the pressure out over the whole mass of itself, this type actually stores most of the pressure in the center in a reasonable predictable rate. Given that we know what the factors are for magma, we can figure out what pressure there should be at the center of the earth and at that pressure there is no way for it to be a liquid anymore and thus has to become super heated metal which is what we believe is at the center of the earth.

Answer 3

Basically you investigate the structure of the earth by using 2 differnet physical methods. The first and more generally used one is the analysis of seismic waves emitted by earthquakes, nuclear explosions or the earth's resonances. As density changes those waves are refracted and reflected and when you record them you can make an inversion to get the density structure of the earth. Also note that seismic waves travel as 2 different kinds of waves, s-waves and p-waves, the latter being polarized longitudinaly whereas the former are polarized perpendicular to the wavedirection.
2 gifs to explain:
p-wave: http://en.wikipedia.org/wiki/Image:Onde_compression_impulsion_1d_30_petit.gif
s-wave:http://en.wikipedia.org/wiki/Image:Onde_cisaillement_impulsion_1d_30_petit.gif

An inherent property of s-waves is that they need a solid to be transmitted, hence they don't exist in the outer core, that's why we know it's a liquid. That the inner core is solid again can be shown because p-waves will induce s-waves when hitting a boundary and vice versa and because of the difference in traveltime and overall behavior a sophisticated inversion will show just that.

The other method applied is magnetotellurics, ie electromagnetic fields induced by the ionosphere into the earth can be measured and will give you some electrical properties of the earths structure, the range being somewhat more limited, ie lower mantle is max.

To bring all those physical properties (remember that's all we can measure, there's no way of remote sensing quartz directly for instance) into a geological context one analyzes magmas and xenolites and also takes the evolution of galaxies into account, ie how much of what element can we realistically expect to find (it's extremely unlikely to find any element heavier than iron in great amounts for example) and what form will it be in under the measured pressures and temperatures.

Answer 4

Most of what we know about the structure of the Earth is inferred from seismic measurements. By measuring the time it takes seismic measurements to travel through the Earth's various layers, we can come up with a very close approximation of the density of those layers. Knowing the average density of the various layers allows us to make educated guesses about their composition. Much of this guesswork has been refined and corroborated by studying core samples and lava flows.

Answer 5

Ever seen LAVA flow ? (Erupting Volcanoes)


Remember pictures of the lava advancing towards and covering houses while bulldozers were making channels to the sea? and hoses trying to make it divert to the man-made channels (One of the Icelandic towns)

as it cooled it was red
nearer the source it was yellow

(sorry to give this obvious answer ...deleting the question is an option)