How are scientists able to study layers of the earth?

I have been sick all week and haven't been to school i have all my notes in my locker ! So if you could tell me the answer that would be helpful.How are scientists able to study layers of the earth?
the elemental composition was determined by ';bowen's reaction series'; which basically factors in the melting points of several elements and therefore computes that hotter lava had to have come from deeper places, and voila! you have what the mantle is made of. (your teacher may not have gone over anything like that.). They study the layers by computation and calculation of seismic waves. Basically when there is an earthquake somewhere, it can be recorded anywhere. Because seismic waves travel differently through different kinds of material (the more solid, the faster, but also the less vibration, the more liquid, the slower, but the greater vibration.) By doing extensive calculations with things like that, they have been able to determine essentially the composition of the inside of the earth. (your teacher may have covered something like that.) We can't go down into the middle of the earth, for reasons that I won't go into right now.How are scientists able to study layers of the earth?
earth quackes have diferent types of waves, diferent ypes of waves have diferent abilities, like S(maybe P not sure right now) waves, they cant cross liquids, so therefore they found that the earth's external nucleous is liquid :D
By studying seismic waves generated by earthquakes geologists learn about the earth's deep structure.