Well, this is a very interesting question. As of today, there are no machines that can carry humans into the center of the earth. If you were to dig a tunnel from your house deep into the earth, as you crawled down the tunnel you would notice two things. As you went deeper, it would start getting hotter and hotter and the pressure would increase until you feel squished. We have no machine that can dig farther than about 8 kilometers (this is a really small number, the center of the earth is almost 6500 kilometers away!!!!), but we are trying all the time to build one.

You can never "get" to the center of the Earth with any machine, because the pressure would be far too great. We can "see" down there indirectly by using the seismic waves from earthquakes that take place on the other side of the world. When there is a large earthquake, it puts a lot of energy into the Earth. Some of that energy travels through the earth in much the same way as sound energy travels through an object. Put your ear down on your desk and hit the desk with your knuckles; you will hear the sound pretty loud.

Certain types of earthquake waves called P waves travel through the Earth as pressure waves, just like sound waves through objects. The Earth has different layers inside it, and as the seismic waves hit each layer, they get bent and scattered, and bounced around, but the echoes of these waves that get recorded by sensitive instruments all over the surface of the Earth tell scientists information about how the waves traveled through the Earth. We can tell things like how long it took them to arrive at a station from the earthquake, how deep they went into the earth, how deep was the center of the earthquake (called the hypocenter), and which layers they bounced off of and got bent through.

So, for example, if there was a big earthquake in China, and we recorded it here in America, we could see some seismic waves that started out at the earthquake itself, but got spread out and bounced around into different travel paths. Some would bounce underneath the crust of the Earth a few times before coming to our recording station; some would get bent through the mantle; some would get bent around the outer core, and that's how we know it is mushy there; and some would follow a path that takes them right through the center of the Earth, through the solid iron-nickel core.

Since the 1930's seismologists have been studying all of the types of seismic waves very carefully, so that now we have ways of recognizing which waves went through the core. Not all earthquakes are large enough to get waves to go that deep or that far, but when there is a big earthquake, all the seismologists around the world study it, and share their knowledge. It is through studying seismic waves that we know the Earth has a mushy outer core and solid inner core.

By studying the gravitational field of the earth we can learn about its overall density, and by studying the magnetic field of the earth we know that there must be a metallic core that conducts electricity and can hold a magnetic field - so we know it must be iron, or an iron-nickel mixture. By combining our knowledge of the speeds of seismic waves through the core of the Earth with the gravity and magnetic information, we can figure out what the core is made of. Does this help you understand? It is kind of like seeing inside your body. You don't want to die and cut yourself open to find out what is inside; but you can use x rays to see inside your body. Nowadays, we know that x rays are not very safe, so doctors use sound waves (called "tomography") to see inside your body. The sound waves bounce around and get recorded just like the seismic waves through the earth. Doctors also use the diamagnetic properties of the water molecules in your body to do magnetic resonance imaging - another way of seeing inside your body without cutting you open. So, that is how we see inside things when we can't actually get inside - we use energy in the form of sound waves, seismic waves, and x rays to "see" inside.

You have asked an interesting question.Did you read the book "Journey to the Center of the Earth" by Jules Vernes or did you see the movie? In science fiction books or movies many things can happen that may not necessarily happen in "real" life. To answer your question in a short way: it is impossible to build a drilling machine that would go all the way to the center of the earth.

But let me explain why this is not possible and maybe your teacher can help you if you don't always understand what I mean.

You have probably learned in school that the earth is divided into four main layers: the inner core, outer core, mantle, and crust. The crust is very thin (only about 25 miles) and rocky and brittle, so it can fracture in earthquakes. It is also not very hot. It would be relatively easy to drill through it. The next layer is the mantle. It is 1800 miles thick and between 1000C to 3500 C hot. Even if we could go through it we would end up at the outer core. Here the temperatures are so high that all metal will melt (4300C and higher). And the further we go inside not only the temperature increases but also the pressure. The inner core has such a high pressure that everything is solid again even though it is very, very hot. The pressure is 3 million times as high as the normal air pressure around you right now. So, how do we learn about the inside of the earth? Most of what we know we learned from seismic waves studies. These sound and shock waves travel differently through the earth layers and we get information if a layer is solid or liquid for example. We know the most about the crust because scientists have drilled into it - about 12 miles deep. And we actually have samples of the upper part of the mantle too, because volcanoes often bring pieces of rock from the mantle to the surface. And believe it or not the nearby crust of the Earth is explored in great detail with echo-sounding techniques, a kind of acoustic radar before scientists do any drilling. This is more effective and less expensive, too.

Thanks for asking this question. Maybe one day you will study material science and work on new materials that can endure a lot of pressure and temperature.

Well it would take a very special machine indeed to get there. The center of the earth is 6400 km down and the deepest well EVER drilled is only 10 km (there are 1.6 km in a mile). < So you can see we have not been able to directly sample the deeper part of the Earth... but one way we can study things is to analyze the SEISMIC waves that travel to the surface of the Earth every time an Earthquake occurs. By studying the travel times of earth quakes, we can build a map of the density and composition of the deep interior of the Earth because the speed of the seismic waves depend on the material that the waves travel through. The temperature rises as one goes deeper into the earth. At the very center the temperature is about 6000 Degrees and furthermore the pressure is so great (due to the rocks that are above) that an object would be squeezed to a very small size indeed.

I hope this answers your question. You can look up any geology book for neat pictures of the structure of the earth and learn more by going to the library and taking out some books on GEOLOGY.