The $1 billion mission to reach the Earth's mantle

CNN) -- Humans have reached the moon and are planning to return samples from Mars, but when it comes to exploring the land deep beneath our feet, we have only scratched the surface of our planet.

This may be about to change with a $1 billion mission to drill 6 km (3.7 miles) beneath the seafloor to reach the Earth's mantle -- a 3000 km-thick layer of slowly deforming rock between the crust and the core which makes up the majority of our planet -- and bring back the first ever fresh samples.

It could help answer some of our biggest questions about the origins and evolution of Earth itself, with almost all of the sea floor and continents that make up the Earth´s surface originating from the mantle.

Geologists involved in the project are already comparing it to the Apollo Moon missions in terms of the value of the samples it could yield.

However, in order to reach those samples, the team of international scientists must first find a way to grind their way through ultra-hard rocks with 10 km-long (6.2 miles) drill pipes -- a technical challenge that one of the project co-leaders Damon Teagle, from the UK's University of Southampton calls, "the most challenging endeavor in the history of Earth science."