Gone But Not Forgotten
- Jul 4, 2009
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The Deepest Hole
To the surprise of the researchers, they did not find the expected transition from granite to basalt at 3-6 kilometers beneath the surface. Data had long shown that seismic waves travel significantly faster below that depth, and geologists had believed that this was due to a “basement” of basalt. Instead, the difference was discovered to be a change in the rock brought on by intense heat and pressure, or metamorphic rock. Even more surprisingly, this deep rock was found to be saturated in water which filled the cracks. Because free water should not be found at those depths, scientists theorize that the water is comprised of hydrogen and oxygen atoms which were squeezed out of the surrounding rocks due to the incredible pressure. The water was then prevented from rising to the surface because of the layer of impermeable rocks above it.
Another unexpected find was a menagerie of microscopic fossils as deep as 6.7 kilometers below the surface. Twenty-four distinct species of plankton microfossils were found, and they were discovered to have carbon and nitrogen coverings rather than the typical limestone or silica. Despite the harsh environment of heat and pressure, the microscopic remains were remarkably intact.
The Russian researchers were also surprised at how quickly the temperatures rose as the borehole deepened, which is the factor that ultimately halted the project’s progress. Despite the scientists’ efforts to combat the heat by refrigerating the drilling mud before pumping it down, at twelve kilometers the drill began to approach its maximum heat tolerance. At that depth researchers had estimated that they would encounter rocks at 100°C (212°F), but the actual temperature was about 180°C (356°F)– much higher than anticipated. At that level of heat and pressure, the rocks began to act more like a plastic than a solid, and the hole had a tendency to flow closed whenever the drill bit was pulled out for replacement. Forward progress became impossible without some technological breakthroughs and major renovations of the equipment on hand, so drilling stopped on the SG-3 branch. If the hole had reached the initial goal of 15,000 meters, temperatures would have reached a projected 300°C (572°F).