Earth’s core may contain 45 oceans’ worth of hydrogen

Earth’s core could contain the equivalent of 45 oceans of hydrogen

By Stéphanie Pappas edited by Andrea Thompson

Earth’s core could contain up to 45 oceans of hydrogen, according to a new study, an estimate that suggests the planet formed from a disk of gas and dust rich in the lightest element in the universe.

The new research, published today in Natural communicationsalso suggests that Earth’s water has accompanied the planet since its formation rather than having been brought in later by impacts from comets and other icy bodies. “It really changes the way we think about where our water comes from,” says Hilke Schlichting, a professor of earth, planetary and space sciences at the University of California, Los Angeles, who was not involved in the research.

The Earth’s core is primarily made of iron, but it is not dense enough to be composed entirely of this element. Determining what percentages of lighter elements make up the core can reveal a lot about how the planet formed. But the core is too far away to measure directly, so researchers must rely on computer simulations and high-temperature laboratory experiments that squeeze tiny amounts of various elements into diamond anvil cells under the temperatures and pressures of the Earth’s center.

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Hydrogen is a slippery element in these experiments, however, because it is very light and diffuses easily, says Anat Shahar, a planetary scientist at the Carnegie Institution for Science in Washington, DC, who was not involved in the new research.

In the new study, Dongyang Huang, professor of earth and space sciences at Peking University in China, and his colleagues found a way to locate hydrogen. They pinched tiny samples of iron (representing the core) and hydrated silicate glass (representing Earth’s early magma oceans) between diamond anvils, heated the samples to about 4,827 degrees Celsius (about 8,720 degrees Fahrenheit), and pressed them to pressures of 111 gigapascals.

The team then shrunk these already tiny samples into needles with a tip of only about 20 nanometers and bombarded the needles with a focused ion beam to peel off the atoms one by one for analysis. The results revealed how silicon, oxygen and hydrogen bond within iron during the formation of an Earth-like planet. These ratios allowed Huang and his colleagues to extrapolate the amount of hydrogen present in the core; they estimate that the element makes up between 0.07 and 0.36 percent of the core by weight. This translates to the equivalent amount of hydrogen in the water of nine to 45 oceans.

This amount of hydrogen in the core could only have appeared during the initial formation of the Earth, says Schlichting, who adds that work by his group and others now points to the same conclusion. This means that the water cycle has played a role on our planet since the core began to cool and hydrogen, silicon and oxygen began to crystallize there about 4.5 billion years ago, Huang explains.

This crystallization, he says, would have created convection in the core, providing a “driving force for an ancient geodynamo to generate the Earth’s magnetic field, essential for the Earth’s development into a habitable place.”

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