A team of scientists is preparing to drill through the Earth's crust for the first time to the mantle below.
The BBC reports the team will soon start drilling beneath the Pacific Ocean to test the viability of such an operation and say an attempt to reach the mantle could begin in 2018.
The project is taking place off Costa Rica. It will attempt to reach some 2km beneath the ocean floor.
Writing in the journal Nature, the scientists say their ultimate goal is to obtain even deeper samples - from the mantle layer below the crust.
Obtaining these rocks would provide a geological treasure trove "comparable to the Apollo lunar rocks" they write.
Scientists already have a range of samples from deep inside the Earth.
Some of these were lifted up in the processes that built Earth's mountain ranges, and others have come up in the lavas of volcanoes.
But the BBC reports all were altered in some way by the means that brought them to the surface, and scientists would dearly love to see pristine specimens.
Drilling into the mantle on land is impractical because the continents are where the crust is thickest - some 30km to 60km thick.
Going through the younger, thinner crust of the ocean floor has the advantage that scientists need drill to only about 6km of depth - but this option has the particular difficulty of setting up and operating a rig at sea.
Researchers will test the necessary techniques in the next few years, and assess three potential Pacific Ocean sites.
A giant Japanese ship, which is capable of carrying 10km of drilling pipes, will host the project.
