This fascinating article describes the scientific enterprise. Among the things they discovered:

• “For decades, geologists had interpreted a prominent seismic boundary deep beneath the continents as the transition from granite to basalt—the dense volcanic rock that forms most of the ocean floor. But Kola never hit basalt. The supposed boundary was nowhere to be found. Instead, the drill continued through more granitic and metamorphic rock, showing that the seismic boundary did not mark a change in rock type at all. It marked a change in how the same rocks behaved under immense pressure and temperature.”
• “Nearly 22,000 feet beneath the surface, drill cores contained microscopic fossils from two dozen species of plankton that had drifted through an ancient sea more than 2 billion years ago. This showed that even after billions of years of burial deep within the continental crust, unmistakable evidence of some of Earth’s earliest life had survived.”
• “Between 16,000 and 23,000 feet, the borehole encountered saline water circulating through fractures in crystalline rocks that geologists had long considered essentially dry. Rather than groundwater that had somehow seeped miles underground, the fluids appear to have originated within the crust itself. As ancient minerals were transformed by heat and pressure, they released chemically bound water, while reactions between water and iron-rich rocks generated hydrogen gas, showing that the supposedly inert continental crust was still chemically active billions of years after it had formed.”

So did they journey to the center of the Earth? No – to put it in perspective, the article says 40,000 feet is “higher than the highest commercial flights”. I know this is true having been on such flights, and yet when you are up there in a tin can you have no idea how high you are. Usually you can’t see anything, but I my recent flight I happened to glance down and saw a really fascinating landscape – possibly the Gobi desert? The formations must have been truly massive because you have no sense of scale. Anyway, digging 40,000 feet gets you “barely a third of the way through the continental crust beneath northern Europe.” What this tells me is that not only is the Earth massive, the atmosphere is a teeny, tiny film clinging to its surface.