Question

the deepest borehole ever drilled, the kola superdeep borehole in russia, only reached about 12 km (about 7.5 miles) into earths crust, less than 0.2% of the distance to the center. why cant scientists drill any deeper?

Explanation:

As the depth increases, the temperature rises significantly. At great depths, the high temperature makes the rock soft and plastic, which causes problems for drilling. Also, the pressure increases with depth. The extreme pressure can damage the drilling equipment and make it difficult to maintain the integrity of the borehole.

Answer:

High temperature and extreme pressure at great depths make it difficult for scientists to drill deeper.