What is the deepest hole ever dug by humankind?
What do you get when you combine a nuclear explosive, several hundred thousand tons of molten iron, a stockpile of grapefruit-size spherical high-temperature probes, and access to the Laser Interferometer Gravitational Wave Observatory (LIGO)?
Why, the world's most ambitious geophysical experiment, of course. You simply use the nuclear explosive to blast open a hole in the Earth's crust, pour in a cocktail of molten iron and probe spheres, and use LIGO to monitor the vibratory feedback of the injected metals as they sink quickly to the Earth's core -- 3,000 kilometers below.
Caltech scientist David J. Stevenson suggested this super-scale measure to probe the Earth's core. But don't think this makes Stevenson a maverick; scientists have been aching to poke massive holes in the Earth's crust for decades.
The probe concept is an offshoot of a Russian scheme called Hot Drop. This project envisioned bundling nuclear waste in large tungsten balls, superheating the spheres to 1,200 degrees Celsius, and then allowing the tungsten constructs to melt through the Earth's crust and into the mantle, where the radioactive material could decay safely.
Needless to say, the Hot Drop concept met resistance from several environmental and political groups, all of whom contend that importing, stockpiling, boiling, and dumping nuclear waste might be a risky proposition.
Still, to give the Russians credit, they are the undisputed kings of deep hole drilling. In fact, the deepest hole ever dug is the result of a Russian effort to probe extreme-depth geology.
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