Scientists have discovered two previously unknown minerals—Fe5O12Hx and Fe7O12Hx—that can absorb and retain even tiny amounts of water. These minerals were found at the boundary between Earth's mantle and core, a region previously thought to be completely dry. The discovery challenges long-held assumptions about the composition of the lower mantle, which is mainly made up of two minerals, bridgmanite and ferropericlase, both of which were considered to be water-free. This new finding suggests that the deep Earth may contain water hidden in these newly identified iron oxyhydroxides, which are capable of trapping water molecules without releasing them. To study these extreme conditions, scientists used a technique called the diamond anvil cell, which compresses tiny samples between two diamond tips while heating them with a laser. This method recreates the immense pressure and high temperatures found at the depths of the Earth's mantle. In these experiments, the researchers observed the formation of Fe5O12Hx and Fe7O12Hx, which can absorb water even when only trace amounts are present. These minerals act like molecular sponges, retaining water indefinitely. Because they are denser than surrounding rocks, they would slowly sink toward the mantle-core boundary, where they could have been trapped for billions of years. The presence of these hydrated minerals may explain some of Earth's most mysterious geological features. For decades, scientists have puzzled over ultra-low velocity zones—regions just above the core where seismic waves travel much slower than expected. These zones have remained unexplained until now. The newly discovered iron oxyhydroxides, which are both dense and water-rich, offer a plausible explanation for these anomalies. However, while the experiments confirm the stability of these minerals under deep mantle conditions, they do not yet confirm their presence in the Earth's interior. If these minerals exist in the deep mantle, they could play a significant role in Earth's geological processes. As pressure decreases near the surface, these minerals might release their trapped water, contributing to volcanic activity and mantle plumes. This water could act as a lubricant, helping tectonic plates move and influencing long-term climate patterns. The origin of this water is still uncertain—it may have been present since Earth's formation or delivered through processes like subduction. This discovery highlights how much Earth still has to reveal about its hidden inner workings, emphasizing the importance of continued scientific exploration.