Earth’s core, long understood to be primarily iron, may harbor a surprising and substantial reservoir of hydrogen – potentially enough to form dozens of Earth’s oceans, according to new research published on in Nature Communications. This discovery, stemming from innovative laboratory experiments, could reshape our understanding of the planet’s formation and the origins of Earth’s water.
For years, scientists have attempted to determine the composition of Earth’s core, a region inaccessible to direct observation. Previous estimates of hydrogen levels relied on indirect measurements, adding hydrogen to iron and observing the resulting volume changes. These methods yielded widely varying results. The new study, led by geodynamicist Motohiko Murakami of ETH Zurich, takes a more direct approach, simulating core conditions in a laboratory setting.
Murakami and his team created artificial core samples – iron shards encased in hydrogen-bearing glass. These samples were then subjected to immense pressure using a powerful mechanical press, and heated to a scorching with a laser. These extreme conditions mimic those found deep within Earth, allowing the researchers to observe how hydrogen behaves within an iron matrix.
Under these conditions, the samples melted into iron blobs containing silicon, hydrogen, and oxygen. This process mirrors the conditions present during Earth’s early formation, when the planet was largely a molten magma ocean. After rapidly cooling and solidifying the samples, the researchers employed a specialized probe to map the distribution of elements within the resulting structures. They discovered tiny formations where silicon and hydrogen were consistently found in a one-to-one atomic ratio.
This ratio is crucial. Previous research, simulations, and geophysical observations have indicated that Earth’s core contains approximately 2 to 10 percent silicon by weight. Based on this information, and the observed hydrogen-silicon relationship, Murakami and his colleagues estimate that hydrogen constitutes roughly of the core’s total weight. “That’s nine to 45 oceans” of water, Murakami stated.
It’s important to note that the hydrogen within the core isn’t present as liquid water. Instead, it exists as elemental hydrogen. However, as this hydrogen rises into the mantle, it reacts with abundant oxygen present in the mantle rocks, forming water. This process suggests a potential link between the core’s hydrogen reservoir and the presence of water on Earth’s surface.
The implications of this finding extend beyond understanding the planet’s composition. The release of hydrogen into the mantle, and its subsequent conversion to water, could influence the melting point of mantle rocks. Lowering the melting point could facilitate magma generation and contribute to volcanic activity, potentially playing a role in the geological processes that shape our planet’s surface.
The study also offers insights into the long-standing debate about the origin of Earth’s water. Traditionally, it has been hypothesized that much of Earth’s water was delivered by impacts from comets and other icy bodies. However, the substantial amount of hydrogen detected within the core suggests that a significant portion of Earth’s water may have been present from the planet’s earliest stages of formation, originating from the gas and dust cloud from which the solar system arose.
Hilke Schlichting, a professor of Earth, planetary and space science at the University of California, Los Angeles, who was not involved in the research, commented that the findings “really changes the way we think of where our water comes from.”
While this research provides compelling evidence for a substantial hydrogen reservoir within Earth’s core, further investigation is needed to refine these estimates and fully understand the complex interplay between the core, mantle, and surface. Ongoing research will likely focus on refining laboratory simulations and developing more sophisticated models of Earth’s interior to better constrain the amount and behavior of hydrogen within our planet.
