Geologists have drilled deeper than ever before into material from the Earth's mantle – more than three-quarters of a mile (1.2 km). The sample offers a glimpse into geology and even life in a deep world normally beyond our reach.
The mantle makes up the majority of the Earth’s interior, covering thousands of kilometers between the crust and the core. Described as having the consistency of caramel, the mantle is a soft, semi-solid structure that contains a different mineral composition than what we see here on the surface.
The problem is that it's hard to study the mantle directly because it's usually about 25 miles (40 km) below the rocky crust. Fortunately, there are areas where the crust is much thinner and mantle material reaches all the way to the surface. And new rock cores have been drilled from such a place.
An international team of scientists set out to the Mid-Atlantic Ridge, a chasm on the seafloor of the North Atlantic Ocean that formed as the Eurasian Plate slowly separates from the North American Plate. Here, mantle rock called peridotite seeps upward and reaches the seafloor.
And now, we have the largest sample ever collected. The team drilled an astonishing 4,160 ft (1,268 m) into the peridotite, removing 71% of the rock. By comparison, the previous record was only 659 ft (201 m) deep.
Johan Lissenberg
The sample was collected by the research vessel JOIDES Resolution, which used a crane to drill into an underwater mountain range called the Atlantis Massif near the Mid-Atlantic Ridge. The scientists apparently planned to collect only the same amount of samples as the previous record, but they found the task surprisingly easy and much faster than they expected, so they essentially kept drilling for the entirety of the expedition.
A team of 30 scientists on the ship analyzed the samples as they came in. The peridotite wasn't pristine mantle material — the rock had interacted extensively with seawater and had become “serpentinized,” taking on a texture that looked like “snake skin.” The peridotite was also interspersed with a number of other types of rocks, suggesting that there might not be as clear-cut a boundary between the crust and mantle as scientists had thought.
Lesley Anderson
The study wasn't just of geological interest, either. The team also collected samples of microorganisms living in different parts of the sample to study the chemical reactions that produce the hydrogen and other molecules that life would need to thrive there.
“We will use these samples to investigate the limits of life in this deep subsurface marine ecosystem, improving our understanding of its origins and helping to define the potential for life beyond Earth,” said Professor Gordon Southam, co-author of the study. “Nickel is essential in hydrogenase, the key enzyme that enables these ancient bacteria to use hydrogen in these extreme environments, so we are now tracking this through the mantle rock.”
The research was published in the journal Science.
Source: University of Queensland via Nature