At www.smithsonianmag.com/science-nature/decades-long-quest-still-earth-man… … great article – very interesting. The ingenuity of humans (or some of them). Geologists are trying to actually drill down into the earth's Mantle.
The article begins with a picture of a broken massive great drill bit. These guys are serious. Big time. Hitting the Mantle is the quest – and they are about to do just that.
Actually, geologists already have some access to rocks from the Mantle – chunks that have been chucked out by volcanoes. What else is in the Mantle? The trick is in finding a place where the crust is thin – and this occurs on the sea floor in some locations. The site chosen is on the SW side of the Indian Ocean, 808 miles SE of Madagascar (Malagasy). This patch of sea floor is a flat plateau and just 2300 feet below the waves. It is thought the crust there is just 1.6 miles thick. That is a big slab of rock to drill into – yet other parts of the sea floor are much thicker.
See also video at www.sciencefriday.com/segments/digging-deep-into-the-crust-of-the-earth/