PUNTARENAS, Costa Rica - Scientists set off from Costa Rica on Sunday to drill a hole deep under the sea and directly extract rocks from record depths that could add to the understanding of climate change.

The rocks dug up from the lower part of the Earth's crust in the coming weeks will be the closest anyone has come to the vast, churning part of the planet called the mantle, which lies between the crust and the core.

On a 140-meter ship that resembles an oil platform, the 30-member scientific team will bring back rocks from 2 kilometers beneath the sea off Costa Rica's Pacific coast.

"This will be a big step forward, but we're still not getting to the mantle - the mantle is still 3 km away," said the expedition's co-chief, Damon Teagle, of Britain's University of Southampton.

An examination of rocks from the crust and mantle could shed light on how tectonic plates - vast pieces of the Earth's crust - formed and how they move. When the plates move against one another they can cause earthquakes.

Scientists also think details about the composition of the lower crust might help them better understand climate change.

The world's oceans trap greenhouse gases such as carbon dioxide, making the oceans important for models that try to predict how these gases fuel climate changes from global warming to altered weather patterns.

Scientists speculate the rocks beneath the sea might also play a role in capturing carbon.

"This carbon which is eventually trapped in the rocks through interactions with the seawater is something we want to put some numbers on," said the mission's other co-chief, Benoit Ildefonse of Montpellier University in France.

This will be the team's fourth visit to the same hole off Costa Rica, which was picked because part of the crust is especially thin there. Drilling in the location started in 2002.

Getting to the mantle could still be a decade away, said Teagle, who compared the task to a moon mission.

"A certain amount of going to the moon was just about going to the moon," he said. "But they also brought back rocks."

Reuters