The deepest hole in the world

Chalk it up to man's inquisitive nature and his capricious propensity for exploration that eventually he would endeavour to dig a hole so deep that he could dig no more. Well, it's been done, and in fact some time ago. A deep hole project initiated in 1962 by Russian geologists led to their decision to drill into the Kola Peninsula, near Finland in 1965. After much preparation and construction, the drilling began in 1970. The goal was to drill down to a depth of 15,000 meters.

In 1992 the drilling stopped because it was found, much to the surprise of the scientists, that the rock that they were drilling into had become too gooey to continue. The temperature had reached 356 degrees Fahrenheit, or 180 degrees Centigrade, much higher than projected. At these pressures the rock displayed plastic properties, and would flow back into the hole when the drill bit was retrieved for replacement. In 1994 the project was abandoned. The experiment had succeeded in creating a hole about nine inches wide and 12.262 kilometers deep. The thickness of the Earth's crust ranges from twenty to eighty kilometers measured on dry land.

How does one go about drilling the deepest hole imaginable? Well, for one thing, it is not possible to apply conventional drilling methods using a rotating shaft and then incrementally adding extensions. This gets very difficult as the hole grows deeper. The solution is to use pneumatic pressure to rotate the drill bit at the end of the shaft by pumping a lubricant through it. The only limitations would then be on the ability of the drill bit to continue biting through the rock, a function of the consistency of the rock itself.

Many surprising things were learned. Seismic evidence predicted a transitional change in the crust from granite to basalt at the depth of between 3-6 kilometres. The difference in seismic reading was actually discovered to be the result of a change in the granite itself due to the intense heat and pressure forcing water to saturate into the rock. The rock above this depth was impermeable, preventing the water from rising to the surface.

Microscopic fossils were found at depths of almost 7 kilometres. Many species of fossilized plankton were discovered with coverings of carbon and nitrogen instead of the typical limestone and silica. The oldest rock found at the greatest depths were estimated to be about 2.6 billion years old.

The United States has embarked on drilling projects of its own. The Deep Sea Drilling Project (DSDP) and the Ocean Drilling Program (ODP) have evolved into the Integrated Ocean Drilling Program (IODP). The objective is to drill through the crust at locations on the ocean's bottom, where in places the crust is only 3 kilometers deep. The project is not so much involved with drilling as deep as possible but with conducting research on the composition and history of the core samples retrieved during the missions. The mission statement:
"The Integrated Ocean Drilling Program (IODP) is an international research organization that conducts seagoing expeditions to study the history of the Earth recorded in sediments and rocks beneath the ocean floor."
Among the discoveries to date include how bacteria produce propane in the deep seafloor; the discovery of frozen natural gas at unexpectedly shallow depths below the seafloor;and the discovery of a fossil magma chamber lying only 1.4 kilometres beneath the seafloor.

And yet the deepest hole in the world has managed to penetrate only 0.2 percent of the way to the core. We can only speculate as to what lies beneath what we have not yet seen.