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The deepest hole in the world is on the Kola peninsula of Russia near the Norwegian border. This hole is being drilled for scientific study purposes and is currently over 12,200 meters deep.
In 1926, Harold Jeffreys hypothesized that a transition zone within the crust, identifiable on seismic records as a “jump” in seismic velocity, could be attributed to a change in rock type from granite to a denser basalt. The deepest hole in the world being drilled at the Kola well has now penetrated about halfway through the crust of the Baltic continental shield, exposing rocks 2.7 billion years old at the bottom. One of the more fascinating scientific findings to emerge from this well is that the change in seismic velocities was not found at a boundary marking(Jeffreys’ hypothetical transition from granite to basalt), but it was at the bottom of a layer of metamorphic rock that extended from about 3.5 to about 9.8 km beneath the surface. This rock had been thoroughly fractured and was saturated with water. Free water should not be found at these depths. This could only mean that water which had originally been a part of the chemical composition of the rock minerals themselves had been forced out and prevented from rising by a cap of impermeable rock.
This discovery has an impact on geophysical sciences and there is a potential economic impact. This water is very highly mineralized, and is a primary concentrating agent for most ore deposits. The technology for mining at these depths is not yet available. In order to get their single drill hole down as far as they did, the Soviets had to resort to experimental methods. Their chief innovation was that, instead of turning the drill bit by rotating the stem, in the Kola well the bit alone was turned by the flow of drilling mud.
As drilling continues at the deepest hole in the world many scientists are hoping for additional discoveries and a greater understanding of the inner workings and makeup of our planet.
We have written many articles about the deepest hole in the world for Universe Today. Here’s an article about how far the center of the Earth is, and here’s a forum discussion about the drillings through the Earth’s crust.
We’ve also recorded an episode of Astronomy Cast all about planet Earth. Listen here, Episode 51: Earth.