Field of Science

At the Earth's Core

Some days ago the Integrated Ocean Drilling Program announced a new "record" of the scientific vessel "Chikyu" (Japanese for "earth") - the at time deepest (scientific) borehole with 2.300 meters below the seafloor was completed in the 1.180 meters deep, blue sea off Shimokita-Peninsula. The longest rig ever done from board of the Chikyu was 7.740 meters long, however in the open sea the greatest problem is not the water, but drilling in the ground. 

Since old times people - especially geologists - were interested to know about the interior of Earth. The Italian poet Dante Alighieri (1265-1321) imagined an allegoric center of the Earth: a frozen wasteland, not reached by the divine light, where Lucifer is entrapped in eternal ice.

Fig.1. Illustration to Dante's "The Divine Comedy" from the "Codice Urbinate Latino 365" (1480) showing the frozen center of Earth.

The French Sci-Fi author Jules Gabriel Verne (1828 - 1905) based an imaginary "Lost World" in "A Journey to the Center of the Earth" (1864) on more scientific ground. In his novel Verne uses the hollow conduit of an Icelandic volcano to venture inside earth, an idea supported by the geologic models of volcanoes proposed at the time - a single or a series of magma chamber(s) with conduits connecting them to the surface. Geologists assumed that during an eruption the magma reservoir becomes empty and large voids and caverns were left behind. 

Fig.2. This schema, published in the book by German professor of geophysics August Sieberg "Einführung in die Erdbeben- und Vulkankunde Süditaliens" (1914), shows the anatomy of a stratovolcano, with a main conduit, various lateral dikes and a large sill connected to the magma reservoir. In contrast to the sketch, the conduits for magma are in reality only a few meters wide - too small for travel the Center of the Earth.

Verne's vision inspired the wonderful U.S. movie of 1959 "Journey to the Center of the Earth" and was reused in the mediocre "At The Earth´s Core" (1976), even if the last movie was based on the novel "At the Earth's Core*" (1914) by Edgar Rice Burroughs (*considering the display of the "Mole"-vehicle, the supposed cavern with the mythical land of "Pellucidar" is situated in the transition zone of Outer Core - Lower Mantle).




Also the first movie featuring "Superman" touches the subject of a deep-earth civilisation. In "Superman and the Mole Men" (1951) the Mole Men invade earth's surface from the deepest oil well of the world (more than 6 miles/ 9 kilometers deep!).
In fact the deepest boreholes in the real world stopped at more than 12 kilometers - however that's just 0,2% of the radius of earth.
In May 1970, to celebrate the birthday of Lenin, the former Soviet Union initiated the secret project "SG-3" on the Kola-Peninsula. The drilling project planned to study the
Mohorovičić discontinuity, situated at 15 kilometers below the surface of the continents. The project was continued until 1989, when technical and especially financial problems, stopped the drill at 12.261 meters forever.
The United States initiated a similar ambitious project, but decided to drill the thinner oceanic crust (5-10 kilometers thick). Project Mohole started in 1961 and was abandoned in 1966, after recovering 170 meters long cores from the ocean floor in 3.500 meters depth. Modern commercial boreholes reach depths of 2.000-3.000 meters.
 

"Gentleman, the truth is that all our theories are just that, theories. None of us has the least idea of how the earth was really formed. Because the distance between the earths crust and its core is over 6.500 kilometres, and no men has ever descended to a depth of more than 3 miles. So it's obvious, we will never have a glimmer of true knowledge, until we are able to reach a depth of at least a 100 leagues.
- What's your opinion Professor Lindenbrook?
- Well gentlemen, at one point at least I agree with Professor Christophe, the materials of the geologists are not charts, chalk and chatter, but the earth itself. We should never know the truth, until we are able to make that journey, and see for ourselves
."
Dialogue from the movie adaption "The Fabulous Journey to the Center of the Earth" / "Where Time Began" (1976), a Spanish version of Jules Gabriel Verne's novel.

Bibliography:

CARLSON, D.H.; PLUMMER, C.C. & HAMMERSLEY, L. (2009): Physical Geology - Earth Revealed. McGraw-Hill Publ, 9th ed.: 645
SCHICK, R. (2002): The Little Book of Earthquakes andVolcanoes. Springer/Copernicus Books, New York: 164

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