Since the 1950s, humans have tried to reach into the mantle of the Earth, which, if ever accomplished, would definitely qualify as the deepest holes ever drilled. No ore or mineral mine can reach such depths, however. One of the first attempts to dig to the mantle was conducted by the United States. Called Project Mohole, the plan was to drill through the shallow crust under the Pacific Ocean just off Mexico and into the mantle, but lack of funding caused the project to be abandoned in 1966.

Next came the Deep Crustal Drilling Program in 1966, which also ended quickly. Still another program, called the Moho Project, developed into the Deep-Sea Drilling Project, and the more modern Ocean Drilling Project. The results of these drilling programs were a substantial number of holes-usually they were no deeper than 33,000 feet (10,000 meters)-but no record-making depths were achieved.

On land, the Bertha Rogers well in Oklahoma might be the deepest in the United States. This gas well stopped at 32,000 feet (9,753 meters) when it struck molten sulfur. To date, it apparently still holds the deepest hole status on the North American continent.

But the winner of the deepest hole ever drilled on Earth belongs to Russia, where there is an over-40,OOO-foot-deep Gust over 7 miles [12 kilometers]) hole that was dug on the Kola Peninsula by what was then the Soviet Union government.

It took 5 years to drill 4.3 miles (7 kilometers) and another 9 to drill the additional 3.1 miles (5 kilometers). Lack of funding-but not trying-ended the twenty-year project in 1989, at a cost of more than $100 mi1lion. Although the Russians were unsuccessful at reaching the upper mantle, they were able to grab the title for deepest hole in the Earth.