Journey to the centre of Earth
David Adam in Yokohama Saturday June 4, 2005 Guardian
Japanese scientists are to explore the centre of the Earth. Using a giant drill ship launched next month, the researchers aim to be the first to punch a hole through the rocky crust that covers our planet and to reach the mantle below.
The team wants to retrieve samples from the mantle, six miles down, to learn more about what triggers undersea earthquakes, such as the one off Sumatra that caused the Boxing Day tsunami. They hope to study the deep rocks and mud for records of past climate change and to see if the deepest regions of Earth could harbour life.
Asahiko Taira, director general of the Centre for Deep Earth Exploration in Yokohama, near Tokyo, said: "One of the main purposes of doing this is finding deep bacteria within the ocean crust and upper mantle. We believe there has to be life there. It's the same mission as searching for life on Mars."
Rocks in the upper mantle produce compounds essential for life when they react with seawater. "This is a system which we believe created early life. There may be a chance that we can catch the origin of life still taking place today," Prof Taira said.
The 57,500-tonne drill ship Chikyu (Japanese for Earth) is being prepared in the southern port of Nagasaki. Two-thirds the length of the Titanic, it is fitted with technology borrowed from the oil industry that will allow it to bore through 7,000 metres of crust below the seabed while floating in 2,500 metres of water - requiring a drill pipe 25 times the height of the Empire State building.
The deepest hole drilled through the seabed so far reached 2,111 metres.
After final sea trials this year, the scientists will set sail for the deep Pacific where the Earth's crust is thinnest. Drilling is expected to begin next year.
It could take more than a year to drive through miles of crust and reach the mantle, so the ship is fitted with six rotating thrusters controlled by GPS satellites to keep it directly over the hole. The drill is surrounded by a sleeve that contains a shock-absorbing chemical mud, and a blowout valve will protect it should the team strike oil or superheated rock in the crust.
The project is part of an international effort called the Integrated Ocean Drilling Programme which also involves the US and Europe.
Shinichi Kuramoto, one of the Yokohama team, said Chikyu's main objective is to retrieve mantle samples for analysis. "Humans have brought back lunar rocks to understand the universe, yet we have never reached the mantle which accounts for most of earth."
Previously undiscovered bacteria that can survive the anticipated 100C temperatures of the upper mantle could be useful on the surface. Heatproof enzymes isolated from bugs brought back by earlier Japanese drill missions are now used in washing powders.
Cores of rock and sediment from the so-called "earthquake nest" where the mantle meets the crust could also help geologists understand seismic events, and to perhaps give more warning.
"We can estimate how frequently marine sliding or earthquakes occur from learning the history of earth but we still don't know when they will occur in the future.
"We take cores to better understand the mechanisms involved," Dr Kuramoto said.
Sensors placed in the borehole could detect changes in strain, tilt and pressure in the ground miles below the surface. "That will be a great advantage in giving us a few days or hours warning before something happens. Current warning systems in Japan only warn us 10 minutes before a large earthquake strikes. We need real-time data from the exact point."