Anonymous

Its today concept about the core and mantle , by new discoveries and invention it might be replaced ,. This are the only signals and indications we don't have yet a clear and reliable evidence to make it believe. The concepts of isostasy adjustment , convection current and plate tectonics are with its strong evidences that is why now a days we believe their existence.

Anonymous

we don't know. We have indications that lead us to believe

Anonymous

either the earth is hollow or it has a core and mantle. take your pick. The earth rotates, so the core and mantle have to rotate along with it, did you expect it to be stationary?

Anonymous

Fifth, we know the composition of the Earth's crust and its mantle, by examining samples of them. For the lower mantle, we use experiments of the effect of pressure on upper (shallow) mantle minerals to predict the mineralogy of the lower reaches of the mantle. We then pass seismic waves through it in the lab to see if our experimental rocks match the observations. Six, now that we know the size, mass and composition of the whole Earth, its crust, and its mantle, we can contruct a balance sheet of materials and see which chemical elements aren't in the crust (including atmosphere and hydrosphere) or mantle that we know should be on the Earth. These must be in the core.

Anonymous

Seismic tomography is a technique for imaging the subsurface of the Earth with seismic waves produced by earthquakes or explosions. P-, S-, and surface waves can be used for tomographic models of different resolutions based on seismic wavelength, wave source distance, and the seismograph array coverage. The data received at seismometers are used to solve an inverse problem, wherein the locations of reflection and refraction of the wave paths are determined. This solution can be used to create 3D images of velocity anomalies which may be interpreted as structural, thermal, or compositional variations. Geoscientists use these images to better understand core, mantle, and plate tectonic processes.

Anonymous

seismic tomography is how we interpret the structure. Basically an MRI of the earth using sound (seismic) waves. the rotation is inferred for the core based on the magnetic field behavior. Persistent spatial correlation between surface location and subsurface features identifiable in the mantle requires that the mantle moves essentially the same rotational rate as the overlying crust (there is no evident separation of mantle from crust in terms of rotational period; what is below a spot tends to stay there for long time frames). We have a model of the earth system that fits what we observe and serves as a good basis for prediction of other features. It is not "knowing" in the sense of direct observation, but is knowing in the sense of "there are not a lot of options which would show us this and still fit everything else we can observe". But that is the essence of most science, really. We "know" it until we are shown that we have made an error. Most errors in modern science are ones of detail rather than gross concept.

Anonymous

Earthquakes. No, seriously. We don't have the technology to send big enough sound waves through the earth to get a complete picture of what's down there. But megathrust earthquakes provide the perfect opportunity to get a look inside our planet. Recording the reflectivity of megathrust quake waves is how we determined the composition of earth's innards.

Anonymous

Because the combination of earthquakes, big explosions and a worldwide network of Seismographs, give us a "picture" if the INSIDE of the Earth and at different times.