Journey to the Center of the Earth

Updated February 21, 2017 | Factmonster Staff

Journey to the Center of the Earth

For forty years, scientists have attempted to drill deep into the ocean’s crust, an enterprise promising significant insight into the planet’s geological history. In the 1950s, the highly ambitious Mohole project sought to drill seven miles into the sea floor, all the way through the extremely dense ocean crust to the planet’s middle layer, the mantle. But the project was abandoned in 1966 as exorbitantly expensive and impractical—no drill was up to the task, and the project’s deepest hole, after nearly a decade of research, planning, and drilling, reached just 601 ft into the ocean’s crust.

But in April 2006, a team of scientists reported success on a more modest ocean drilling project, which has yielded some impressive findings. Researchers involved in the Integrated Ocean Drilling Program (IODP) managed to drill nearly a mile into the ocean crust, collecting the first intact sample ever of all the crust’s various layers, including the very deepest layer, composed of igneous rock called gabbro. Gabbro has been discovered during other ocean drilling projects—in these cases, geological disturbances had shifted the gabbro closer to the ocean’s surface. But this is the first instance in which gabbro has been found in situ.

The drilling of Hole 1256D, as the 3,796-foot-deep bore hole is unceremoniously named, took place 400 miles west of Costa Rica in the Pacific Ocean, with the 120 scientists housed aboard the research ship Joides Resolution. The location was selected because the ocean crust is thinner there than in most parts of the world. The project began in 2002 and involved three separate voyages, nearly six months of drilling at sea, and twenty-five ten-inch-wide, state-of-the-art drill bits. The Integrated Ocean Drilling Program is an international marine program spearheaded by the U.S. and Japan, and involves 18 other countries. It's considered the world's largest earth science program.

Some scientists have dubbed this intact sample the holy grail to unlocking the secrets of the ocean crust, which in turn will bring broader revelations about our planet. According to Jeff Fox, the director of IODP, “The record of the earth’s history is written in greater clarity in the sediments of rocks on the sea floor than anywhere else.”

Fact Monster/Information Please® Database, © 2005 Pearson Education, Inc. All rights reserved.

Sources +