They've selected prospectivesites under the Pacific Ocean where the crust is at is thinnest - just six kilometres.

Dr Damon Teagle of the UK's National Oceanography Centre in Southampton, is leading the quest. He likens the bid to theretrieval of Moon rocks by the Apollo programme and says samplesfrom the mantle will tell us how our planet was formed and how it's changing.

Dr Teagle says: "Just as the Moon rocks told us about thecomposition of the Moon and how that relates to the early formation of the Earth itself, so will these samples as well."

Next month, the team will begin abid to drill nearly two kilometres down through the ocean floor off the coast of Costa Rica. They say an attempt to reach the mantle could begin as early as 2018, funds and technology permitting.

Neil Bowdler, BBC News