Earth's Core May Hold Vast Hydrogen Reservoir, Revealing Planetary Secrets
Earth's core is now suggested to be the planet's largest store of hydrogen.
A recent study indicates that Earth's core may contain a substantial reservoir of hydrogen, estimated to be equivalent to 9 to 45 times the total hydrogen in the planet's oceans. This significant finding offers insights into the planet's formation, the origin of its water, and the generation of its magnetic field.
Discovery and Estimates
Researchers, led by geoscientist Dongyang Huang of Peking University, published their findings in Nature Communications. Their work estimates that hydrogen could constitute between 0.07% to 0.36% of the core's mass, or approximately 0.36% to 0.7% of its total weight. This translates to an estimated 1.35 to 6.75 sextillion kilograms of hydrogen.
Research Methodology
To reach these conclusions, scientists conducted experiments replicating the extreme conditions of Earth's early molten core. These included pressures up to 111 gigapascals and temperatures around 5,100 Kelvin.
Diamond Anvil Cell Experiments
One experimental approach involved a diamond anvil cell, where a small iron ball encased in hydrated silicate glass was subjected to these extreme conditions. This revealed that hydrogen readily mixed with the iron and subsequently bonded with oxygen and silicon within the mixture. This suggests a similar process could have occurred during Earth's core formation billions of years ago.
Atom Probe Tomography
A more recent technique employed was atom probe tomography. This involved melting iron samples with lasers in a diamond anvil cell and then sharpening them into nanoscale needlelike shapes. Under high voltage, individual atoms were ionized and counted, allowing for direct observation of hydrogen and other core elements, capturing 3D images, and measuring chemical composition at the atomic scale. This method focused on observing how hydrogen interacted with silicon and oxygen in nanostructures as the metal cooled, showing an approximate 1:1 ratio of hydrogen to silicon. This advanced approach is noted as distinct from earlier methods that relied on X-ray diffraction, which yielded widely varying estimates.
Implications for Earth's History and Characteristics
The study's findings contribute to the understanding of several fundamental aspects of Earth:
- Water Origin: Lead author Dongyang Huang suggested that the estimate implies Earth acquired most of its water during its initial formation over 4.6 billion years ago, within the first million years of its history, rather than primarily through later comet impacts as some theories propose.
The core is suggested to be Earth's largest hydrogen reservoir, with the mantle, crust, and surface holding progressively less.
- Magnetic Field Generation: The observed interplay between silicon, oxygen, and hydrogen in iron nanostructures offers insights into how heat may have been released from the core into the mantle, a process considered crucial for establishing Earth's magnetic field.
- Planetary Formation: Rajdeep Dasgupta, a professor at Rice University not involved in the study, noted that hydrogen could only enter the core-forming metallic liquid if it was present during Earth’s main growth phases. The research highlights the role of volatile elements in Earth's formation.
- Broader Planetary Context: The research suggests that water could be far more deeply integrated into Earth than previously assumed. It also implies that other rocky planets, even seemingly arid ones, might harbor hidden water deep within their interiors.
Uncertainties and Future Research
Researchers cautioned that the indirect nature of the approach introduces uncertainties, and further work is required to confirm and refine the estimates. Factors such as potential hydrogen escape during decompression in experiments were not included in the new calculations, and other chemical interactions may affect calculations.
Kei Hirose, a professor at the University of Tokyo, suggested the actual amount of core hydrogen could be higher, based on prior work that estimated core hydrogen at 0.2% to 0.6% by weight.
The study contributes to the broader understanding of how essential elements for life, including hydrogen, carbon, nitrogen, oxygen, sulfur, and phosphorus, were delivered and distributed during Earth's formation.