Crack in the World (1965)

Dr. Stephen Sorenson plans to tap the geothermal energy of the Earth's interior by means of a thermonuclear device detonated deep within the earth. Despite dire warnings by fellow scientist Ted Rampion, Dr. Sorenson proceeds with the experiment after secretly learning that he is terminally ill.

This experiment causes a crack to form and grow within the Earth's crust, which threatens to split the Earth in two if it is not stopped in time.