They've selected prospective sites under the Pacific Ocean where the crust is at its 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 the retrieval of Moon rocks by the Apollo programme and says samples from the mantle will tell us how our planet was formed and how it's changing.

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

Reporter: Next month, the team will begin a bid 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.

prospective

possible or suitable

quest

long, difficult search or mission

likens

says something is similar

retrieval

getting back

samples

small parts of something, which have been collected

composition

things that are in an object, and how they are arranged

relates

is connected

bid

attempt or aim

to drill

to operate a machine which creates a hole in something solid

permitting

allowing, or making something possible