Record-breaking hole into the Earth’s mantle

 Scientists drilled record-breaking hole into the Earth’s mantle 

In what can only be described as a herculean accomplishment, a team of scientists has succeeded in bringing to the surface a long, 1,268-meter section of rocks from the Earth’s Mantle. This layer, hidden beneath the crust, forms the largest chunk of our planet. The insights gained from this discovery open doors to a profound understanding of our planet’s inner workings, offering a peek into life’s origins, the causes behind volcanic activities, and the global cycles of elements vital to our existence such as carbon and hydrogen. A team of geophysicists say that an enormous mass shifted deep beneath the Earth's surface 18 years ago. The record-breaking mission offers an unprecedented opportunity to study the geology of our planet’s largest layer. To understand the mantle, the largest layer of Earth’s rocky body, scientists drill deep cores out of the Earth and recovered serpentinized peridotite which forms when saltwater interacts with mantle rock. Although this is the deepest into the mantle scientists have ever drilled, the mission didn’t uncover pristine mantle which lies beyond the Mohorovičić discontinuity, or Moho, boundary.

The Earth is composed of four primary layers: the crust, mantle, outer core and inner core. At the surface, we find the crust, which is thin and solid, primarily made of rock, representing the layer where we reside. Below the crust lies the mantle, a substantial layer of semi-solid rock which flows gradually over time. This dynamic layer is crucial, as it drives the movement of tectonic plates, resulting in earthquakes and volcanic activity. If you want to understand the geology of our home planet, studying the mantle is a great place to start. Separating the planet’s rocky crust and the molten outer core, the mantle makes up 70 % of the Earth’s mass and 84 % of its volume. But despite its outsized influence on the planet’s geologic processes, scientists have never directly sampled rocks from this immensely important geologic layer. Delving deeper, the outer core consists of liquid metal, predominantly iron and nickel and is responsible for generating Earth’s magnetic field through its movements. At the very centre, we encounter the inner core, a dense, solid sphere of iron and nickel. Despite enduring extreme heat, the extraordinary pressure keeps this inner core solid. Each layer not only contributes to the structure of our planet but also plays a vital role in processes which develop our environment.

And that’s understandable, especially when you consider that the crust is roughly 9 to 12 miles thick on average. Luckily, that average contains outliers, areas of the world where the crust is actually incredibly thin and faulting exposes the mantle through cracks. One such area is the Mid-Atlantic Ridge, specifically near an underwater mountain called the Atlantis Massif. On the south side of this massif is an area known as the Lost City, a hydrothermal field whose vent fluids are highly alkaline and rich in hydrogen, methane, and other carbon compounds. This makes the area a particularly compelling candidate for explaining how early life evolved on Earth. Additionally, it contains mantle rock which interacts with seawater in a process known as “serpentinization,” which alters the rock’s structure and gives it a green, marble-like appearance. The mantle rocks were procured from a tectonic window on the Mid-Atlantic Ridge during Expedition 399 of the JOIDES Resolution, appropriately titled “Building Blocks of Life, Atlantis Massif,” in spring of 2023. This accomplishment marks an epoch in Earth sciences. The international team, operating under the International Ocean Discovery Program (IODP), has secured these ancient rocks for detailed analysis. They will now serve as keys to our understanding of Earth’s geological and biological history.

It was here, 800 meters south of this field, a 470-foot-long research vessel rented by the US National Science Foundation, extracted a 1,268-meter core containing abyssal peridotites, which are the primary rocks that make up the Earth’s upper mantle. Although this makes this particular drill core the deepest sample of the mantle yet, going that deep into the rock wasn’t the goal of this record-breaking expedition. “We had only planned to drill for 200 meters, because that was the deepest people had ever managed to drill in mantle rock,” Johan Lissenberg, a petrologist at Cardiff University and co-author of the study, said. The drilling was so easy that they progressed three times faster than usual. The team eventually drilled a staggering 1,268 meters, and only stopped due to the mission’s limited operations window.

The rock samples are far from ordinary. Their unique makeup reveals secrets of processes that took place as these rocks ascended from the deep recesses of the Earth to the surface. Professor Lissenberg notes, “Our study begins to look at the composition of the mantle by documenting the mineralogy of the recovered rocks, as well as their chemical makeup.” Interestingly, they contain less of the mineral pyroxene and more magnesium than anticipated. This points to the mantle undergoing considerably more melting than previously believed, which in turn, helps explain how magma forms and eventually leads to volcanic eruptions. Andrew McCaig, study co-author and University of Leeds scientist, said that, according to a preliminary analysis of the rock, the core’s composition contains a variety of peridotite called harzburgite that forms via partial melting of mantle rock. It also contained rocks known as gabbros, which are coarse-grained igneous rocks. Both of these rocks then chemically reacted with seawater, changing their composition.

Pathways discovered within these rock samples indicate the routes magma took towards the Earth’s surface. These revelations underscore a better understanding of how magma originates in the mantle, moves upwards, and eventually powers volcanic eruptions. “This is important because it tells us how the mantle melts and feeds volcanoes, particularly those on the ocean floor that account for the majority of volcanism on Earth,” explains Professor Lissenberg. Understanding this interplay between mantle melting and volcanic activity is a critical piece in Earth’s geological puzzle. While this core represents an incredibly opportunity to learn more about the Earth’s mantle, as well as give an in-depth look at the geologic substrate upon which the Lost City rests, the mission didn’t quite complete the “grand challenge” of crossing the Mohorovičić discontinuity. Otherwise known as the Moho, the Mohorovičić discontinuity is recognized as the true boundary between the crust and pristine mantle.

The mantle rocks offer key insights not just into geological processes, but also into how life on Earth might have originated. The mineral olivine, abundant in mantle rocks, reacts with seawater to produce hydrogen and other molecules, a process potentially fundamental to the creation of early life conditions. Dr. Susan Q. Lang from the Woods Hole Oceanographic Institution said “The rocks that were present on early Earth bear a closer resemblance to those we retrieved during this expedition than the more common rocks that make up our continents today,”. This discovery offers a glimpse into conditions billions of years ago. The journey of the Expedition is far from complete. The team will continue to examine the mantle samples to unravel a myriad of scientific mysteries. Dr. Andrew McCaig , the co-chief scientist of the expedition from the University of Leeds, sheds light on the extensive implications of this research. “Our new deep hole will be a type section for decades to come in disciplines as diverse as melting processes in the mantle, chemical exchange between rocks and the ocean, organic geochemistry, and microbiology,” McCaig concluded. 

Future missions could continue exploring this site near the Atlantis Massif, but sadly, those missions won’t include JOIDES Resolution, the NSF declined to fund more core drilling past 2024. Just as scientists are finally knocking on the door to the Earth’s most ubiquitous geologic layer, the future of these kinds of drilling missions is now uncertain. The recovery of mantle rocks from the ocean’s depths is not just a landmark scientific achievement; it’s a giant leap towards untangling the intricate mysteries of our planet. As scientists like Professor Lissenberg, Dr. Lang, Dr. McCaig, and their colleagues continue to delve into the data, they’re not just increasing our understanding of Earth; they’re also reshaping our perception of our planet and our place within it. It is awe-inspiring to realize that somewhere, deep beneath our feet, the answers to some of life’s grandest questions lay shrouded in mystery. The team’s relentless pursuit of knowledge, their spirit of collaboration, and their unending curiosity serves as a reminder of scientific exploration’s endless potential for future.