The earth’s temperature increases with depth. Measurements made in deep mines and drill-holes indicate that the rate of temperature increase varies from place to place in the world, ranging from 59° to 167°F (15 to 75°C) per kilometer in depth. Actual temperature measurements cannot be made beyond the deepest drill-holes, which are a little more than 6.2 miles (10 kilometers) deep. Estimates suggest that the temperatures at Earth’s center can reach values of 5,000°F (2,760°C) or higher.