I am sure you all spend some time at the beach when you were a kid. And I am also sure that your started digging holes in the sand when you were there. Or maybe you did something like that in your backyard. Anyhow, have you ever wondered how deep you would be able to dig? If you maybe could dig through the whole world? And if yes, why hasn’t anyone done this, yet?
Russian scientists tried this out for real between 1970 and 1994. They dug a hole, the Kola Superdeep Borehole, which got 12.2 km deep in the end. Only being about one third of the thickness of the earth’s mantle, this is even deeper than the deepest point on earth, the Mariana Trench southeast of Japan, which is “only” 11.0 km deep. So why did they stop, when they already bested the Mariana Trench? Well, it just became too hot. The temperature in these depths is around 180 °C and this was obviously too much for the drilling equipment. So they just sealed up the hole and left it.
Is the story over here? No! Just recently the so called 2012 MoHole to the Mantle Project was started. It supposedly costs about one billion dollars. They adventurous plan: starting to dig at the bottom of the Mariana Trench, so the mantle to dig through would be thinner already in the beginning. There weren’t any news after 2012. So, if the project was stopped, I cannot tell, but maybe the diggers just need to collect some courage (and more money).
 http://www.iflscience.com/environment/deepest-hole-world (last access 23.08.2015)
 http://science.howstuffworks.com/environmental/earth/geophysics/dig-hole-to-earths-mantle.htm (last access 23.08.2015)