Scientists report that they may have finally discovered the cause of the mysterious layer of crystal surrounding the Earth’s core, the “seeping water” that flows from the Earth’s surface and interacts with the mineral core of our planet. In the 1990s, geologists discovered a thin layer surrounding the Earth’s outer core, which is a rotating ocean of liquid metal surrounding the solid inner core. The thickness of the layer, called the E-prime layer, or E layer, is more than 100 km (60 miles), which is relatively thin compared to other parts of the Earth’s interior, and is located at a depth of about 2,900 km (1,800 miles) below the Earth’s surface. Scientists had previously assumed that layer E was left behind by ancient iron-rich magma. Other theories assumed that it leaked from the inner core or was formed during the Earth’s collision with a protoplanet, which led to the birth of the Moon and left parts of the nascent world inside the Earth. But none of these ideas has been widely accepted. In a new study published November 13 in the journal Nature Geoscience, scientists discovered that the E layer was likely formed by water seeping from the Earth’s surface via subduction or sinking of tectonic plates, and then interacting with the mineral surface of the outer core. If the new result is correct, it means that the E layer produced large amounts of silica crystals as a byproduct of this reaction, which were fed into the mantle – the massive layer of magma that lies between the Earth’s outer core and crust. In the study, the researchers conducted a series of laboratory experiments to replicate how water interacts with the outer core under extreme pressure. This revealed that the hydrogen present in the water replaces the silica inside the liquid metal, forcing the silica to come out of the metal in the form of crystals. Hence, the E layer is likely to be a hydrogen-rich, silica-depleted layer in the outer core, which contradicts previous assumptions about its composition. Scientists believe it may have taken more than a billion years for the E layer to reach its current thickness, meaning it may be older than the inner core, which solidified about a billion years ago. The new discovery is another sign that our current understanding of how the outer core and mantle interact with each other may be incomplete. It is worth noting that in September 2022, the same research team discovered that seeping water could interact with large reservoirs of carbon in the outer core to create giant diamond “factories” near the core-mantle boundary.
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