“The deepest humans have ever drilled into the Earth’s crust is 12.262 kilometres (40,230 feet) at the Kola Superdeep Borehole on the Kola peninsula of Russia. This drilling took 20 years to complete and is the deepest penetration of the Earth’s solid surface. The crust is the only layer of the Earth that humans have encountered, and it ranges from 3 to 40-plus miles thick. The Earth’s geothermal gradient means that the temperature increases by about 25 degrees Celsius for every kilometre drilled. This makes drilling deeper more challenging, and the pressure within the mantle may be far beyond the strength of any material known today.”
Source: https://quartzmountain.org/article/how-deep-have-we-travelled-into-the-crust
Space may or may not be “the final frontier”, but the fact is we have barely scratched the surface (pun intended) on the crust of our home planet...
A couple of years back a team of geologists in UK wanted to drill through the mantle.................