how do we know for sure that earth has a core?

Question

is there proof that earth has a core? or is it possible it is hollow at the center?

Answer 1

da hammer and eugene n are correct, but here is how. Seismic waves come in several different types. Earthquakes cause most of these types to occur, but the important ones for your question are shear waves (like a sine wave) and compressional wave (like when you push a slinky on the ground). Compressional waves pass through both liquids and solids while shear waves do not pass through liquids.

So the geophysicists have found that there is a shear wave shadow zone on the side of the world opposite an earthquake. Therefore, they surmise that there is a liquid core that does not allow the propagation of shear waves. Theoreticaly studies of heat and pressure within the earth show that there is a solid core at the very heart of the earth because the pressure there overcomes the heat of the earths interior and allows solid nickel-iron to form.

Obviously the above is simplified. There are other effects of the lower mantle and core on seismic waves. One of these is refraction, where the waves are bent (generally away from the core area) when they encounter denser material, so the waves (even the compressional ones, I think) are spread out and don't propagate in a straight line. Some other types of seismic waves are called rayleigh and love waves.

As far as it being hollow..remember that the entire weight of the earth outside the "hollow" would be pressing down from all directions. Such a hollow would immediately fill up as the earth crushed it..the very reason the earth is a (near) sphere, gravitational shaping, mitigates against a void in the center of the earth. A hollow earth does make for fascinating novels and movies, however.

Answer 2

The earth has four layers,the outermost layer in which we live is called the crust.Beneath the crust is the mantle,the mantle is movable and contains hot melted rock.There are about 12 different plates broken up along the upper part of the mantle and the crust.These plates shift and collide, causing earthquakes and volcanic eruptions.Beneath the mantle is the outer core, which is mainly made of melted iron and nickel.Beneath the outer core is what is called the inner core which is SOLID IRON and is HOT,HOT,HOT.
Planetesimals,are small plants the size of asteroids in a swirling cosmic cloud.Minerals,dust and ice crystals collided and stuck together.Eventually gravity pulled more material into each creating larger and denser bodies called planets.

Answer 3

It surmised through soundings of shock waves from various earthquakes and how they propagate through the earth. It's sortof like an untrasound but at a very low frequency.

Answer 4

We came to know about the inner parts of the earth only after we studied the seismograph picture during earthquakes. Visit my photo album to have more knowledge on core of earth.URL is
http://asia.pg.photos.yahoo.com/ph/quake

Answer 5

Seismic imagery