Efforts to drill into the earth’s mantle have failed yet again. An expedition by the Joint Oceanographic Institutions for Deep Sampling, or JOIDES 360, was called of after researchers spent two months in the Indian Ocean. Their mission was to drill below the ocean floor in an attempt to get to the mantle, which is the largest geological layer of the planet.
The plan for JOIDES 360 was to drill into a particularly thin slice of the earths crust where scientists suspect that the mantle rises above what should typically be the crust-mantle boundary. In a blog post at close of the latest JOIDES expedition which failed to reach its targeted depth the team, which comprises of 122 researchers, wrote:
"We may not have made it to our goal of 1300 m, but we did drill the deepest ever single-leg hole into hard rock (789 m), which is currently the 5th deepest ever drilled into the hard ocean crust. We also obtained both the longest (2.85 m) and widest (18 cm) single pieces of hard rock ever recovered by the International Ocean Discovery Program and its predecessors!
Our hopes are high to return to this site in the not too distant future."
Missions to drill into the earth’s mantle began back in the 1960s when geologists first tried to drill down off the Pacific Coast in Baja California. But the earth-bound mission was overshadowed by the more glamorous expeditions to the moon and budget cuts put mantle exploration on the back burner.
Punching through the crust and into the mantle would allow scientists to extract gabbros, the rocks formed from slow-cooling magma caught under earth’s surface. These rocks are expected to hold clues to the earth’s paleoclimate, plate tectonics and possibly even why dinosaurs disappeared. Analysing the chemical composition of the mantle may also provide insights into how it conducts heat and seismic waves.
The key to reaching the mantle is picking the right spot to drill and so far researchers have been unlucky with such expeditions. Samples extracted from ocean ridges where the mantle rises to the ocean floor are thought not to be representative of the overall mantle. In other places the mantle might be too deep or the crust too hot to drill for more than a couple of kilometers.
Even if scientists have failed extract gabbros, rock samples they have retrieved from deep in the crust will give them plenty to study, till they finally get that sample of mantle.