A new scientific revelation reveals that deep in the Earth’s core lies a good amount of hydrogen as well as a large amount of iron. While the iron in the core has always been recognized as dominant, the addition of hydrogen could account for up to 45 ocean equivalents of hydrogen when compared to the amount found in Earth’s oceans today, according to a report just published in Nature Communications.
Scientists have known for many years that pure iron could not account for the density of the Earth’s core. Therefore, they have theorized that there must be some amount of lighter elements incorporated into the core. The most likely candidate for inclusion is hydrogen, being the lightest element in the universe.
New research from Peking University concludes that significant amounts of hydrogen are locked away within the core of the Earth. Previous research made it possible to directly examine the way in which hydrogen behaves under extreme conditions, just as existed at the time of Earth’s creation.
The conditions that existed at the time of Earth’s magma ocean phase were reproduced by using a laser-heated diamond anvil cell to create the temperatures and pressures sustained by the magma ocean. Over 1,800 miles below the Earth’s surface, the temperatures approached those of the sun’s surface. The pressure would crush almost all forms of material into an unrecognizable state.
In order to reproduce conditions experienced within the first few years of Earth’s formation and the magma ocean, the research team performed the experiments utilizing laser-heated diamond anvil cells to achieve the necessary pressures and temperatures. The setup allowed for pressures of 111 gigapascals and a temperature of nearly 5,100 Kelvin.
Samples of iron were placed adjacent to hydrous silicate glass, representing the type of molten rock present on young Earth. When the iron melted due to extreme heat, large quantities of oxygen, silicon, and hydrogen were dissolved into the molten iron. They formed into small clusters within the iron upon subsequent rapid cooling of the sample. These clusters trapped significant amounts of hydrogen.
Atom probe tomography was used by the team to analyze the results of their research. Atom probe tomography is a very high-resolution analysis technique that removes atoms one at a time from a specimen and then creates a three-dimensional (3D) map of the atom’s position using a mass spectrometer.
It operates at a spatial scale of 1 billionth of a meter (1 nm). For the first time ever, scientists were able to directly observe hydrogen within iron-rich materials subjected to such high pressures as were seen in this research study.
The measurement of hydrogen at this resolution presents numerous challenges. One such challenge is that the measurement environment that scientists create within their laboratories often contains residual hydrogen. This may contaminate the resulting measurement. Background hydrogen may represent several percent of the total measurement of hydrogen.
The primary evidence for the presence of hydrogen within the samples studied derives from nucleation of silicon-hydrogen ions in the silicon-oxygen clusters. These silicon-hydrogen ions were consistent with naturally occurring silicon isotope abundances. This further supports the conclusion that the hydrogen detected was bonded within the matrix of silicon, not simply a result of background contamination.
According to the measurement results, hydrogen was present at an abundance of over 30 atomic percent within the cluster structures. The ratio of silicon to hydrogen in the cluster structures was found to be nearly 1:1. This information is critical to achieving an accurate estimation of the hydrogen abundance in Earth’s core.
Using reasonable estimates of how much silicon is located in Earth’s core, and assuming the experimental data provides accurate estimates of the ratio of silicon to hydrogen in the core, scientists have estimated the total mass of hydrogen that may be contained in the core to be between 0.07 and 0.36 percent of the total mass of the Earth. Converted to ocean volumes, this translates to approximately 9 to 45 oceans of hydrogen.
Prior to the research described herein, the estimated abundance of hydrogen in Earth’s core ranged from 10 to 10,000 parts per million. The wide range of estimates resulted from the use of indirect measurement techniques. The studies that have been done in the past looked at how the iron mineral would change its structure when hydrogen interacted with it and added hydrogen. This new approach provides greater insight into the process.
These recently published observations are going to change how you look at Earth’s oceans. For years, there has been much debate among different scientists about whether comets were responsible for the majority of the water on this planet after its formation.
New observations have produced a different interpretation on that subject. If hydrogen’s contribution to Earth mostly came from later cometary bombardments, most of that hydrogen would reside in shallower regions of the Earth. As a result, the existence of a large amount of hydrogen in Earth’s core suggests that it has been present since before the planet formed.
Corresponding author, Dongyang Huang states, “The fact that most of Earth’s water was created in situ during the formation of the planet is a logical conclusion from the dynamical perspective that planetesimals and planetary embryos contributed most of that water and that there were hydrogen ingassing events involving the interaction of a primordial atmosphere and a magma ocean. It would also be consistent with the theory that Earth was mostly formed from materials similar to enstatite chondrites, i.e., that apart from their isotopic similarities to the Earth, enstatite chondrites also have large enough amounts of hydrogen to contribute greater than 3 oceans of water and have terrestrial-like H isotope ratios.”
Hydrogen is the most abundant element in the solar system, yet many researchers have historically described the Earth as cosmochemically dry when compared to several of the other meteorites that have been discovered. As a result of these findings, that label may no longer accurately describe the Earth.
The research group advises that the study’s conclusions have limitations. Hydrogen may have escaped during experiment. Hydrogen may also have been included twice because of background contamination. Additionally, there remains uncertainty regarding the actual amount of silicon contained in the core. Nevertheless, there is still strong evidence that supports a significant reservoir of hydrogen within the core.
Not only does the presence of hydrogen explain the discrepancy between observed density and theoretical density, but it may also play a role in determining how Earth evolved.
Depending on how cool the core is, silicon and oxygen may crystallize out of molten metal. Because hydrogen reduces melting temperatures, this crystallization may be delayed. These types of changes in the formation of the core may affect the functioning of the early dynamo, which provides the mechanism for generating Earth’s magnetic field.
As time passes, the hydrogen-bearing materials may rise toward the core-mantle boundary. This could potentially generate convection currents and deliver heat to the mantle. This is thought to play a role in volcanic activity and in the deep cycle of water. Therefore, below the vast areas of the oceans that we can observe today, there is likely to have been a gigantic reservoir of water that has remained hidden since the birth of the Earth.
The new insights from this research will change the way that scientists model Earth’s water budget. If Earth acquired the vast majority of its hydrogen when the planet formed, models that describe the growth of planets need to take into account the capture of volatiles during this early stage of planetary history. This new insight will help guide researchers as they study other rocky planets.
The new results produced by this study will also further our understanding of how magnetic fields are generated and maintained. The effect of hydrogen on lowering melting temperatures will have a direct influence on both the timing and strength of the creation of a planet’s magnetic field. This is critical because the magnetic field protects planets from the harmful effects of cosmic radiation.
In addition to our understanding of Earth, this research will provide insight into how habitable worlds develop. It will help researchers evaluate distant exoplanets by providing information on when and how water becomes trapped inside a planet.
The findings of this study will also demonstrate new techniques to measure the amount of hydrogen in extreme conditions. They thus pave the way toward future studies in the fields of extreme pressure physics and geochemical studies.
Research findings are available online in the journal Nature Communications.
The original story “Earth’s core may hold 45 oceans worth of hydrogen, study finds” is published in The Brighter Side of News.
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