Earth Sciences and Ecology Question #1404

Adrian, a 9 year old male from Torrance, California asks on April 18, 2003,

How far have scientist been able to dig into the earth surface?

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The answer

Barry Shell answered on April 21, 2003

The deepest research hole ever dug was called Kola and was done by the Russians beginning in 1970. By 1994 it had already reached 12,000 metres (around seven-and-a-half miles). The project stopped around that point.

Ken Hickford, England answered on January 24, 2006

[editor: Ken found a website by David Pratt called the Mysteries of the Inner Earth with more information on the Kola hole. From the site...]

"Microscopic fossils were found at depths of 6.7 km. 24 species were identified to be single-cell marine plants known as plankton. Unlike conventional shells of limestone or silica, these coverings were found to consist of carbon and nitrogen and had remained remarkably unaltered despite the high pressures and temperatures to which they had been subjected.

It is generally assumed that temperature increases with depth. In the Kola borehole, the temperature at 10-km depth was 180°C rather than the expected 100°C. Measurements revealed significant vertical variations in temperature gradient and heat-flux density along the borehole. Overall, the rate of temperature increase rose from 11° to 24°/km down to a depth of nearly 7 km, and then started to decline. Geologists recognize that the rate of temperature increase must drop off sharply at a certain depth as otherwise the mantle would be molten below about 100 km (even at the enormous pressures assumed to exist there), whereas seismic evidence indicates that it is solid."

Also visit the official Kola borehole website with pictures and diagrams of the hole. Interestingly it does NOT go straight down, but wanders a bit.

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