Earth’s core may contain as much hydrogen as 45 oceans
An experiment to determine the amount of the universe’s lightest element in Earth’s core suggests that the planet’s water has been there since the beginning.
A new study has found that Earth’s core may contain the equivalent of 45 oceans’ worth of hydrogen — an estimate that suggests the planet formed from a gas and dust disk that was rich in the universe’s lightest element.
New research, published today nature communicationIt also suggests that Earth’s water has been present since the planet’s formation, rather than being acquired later by impacts from comets and other icy bodies. “This 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 composed mostly of iron, but it is not dense enough to be composed entirely of that element. Figuring out what percentage of lighter elements make up the core could reveal a lot about how the planet formed. But the core is too far away to measure directly, so researchers have to rely on computer simulations and high-temperature laboratory experiments that squeeze tiny amounts of different elements into diamond anvil cells under the temperatures and pressures of Earth’s center.
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However, hydrogen is a slippery element in these experiments, because it is so light and easily diffused, says Anat Shahar, a planetary scientist at the Carnegie Institution for Science in Washington, D.C., who was not involved in the new research.
In the new study, Dongyang Huang, a professor of earth and space sciences at Peking University in China, and his colleagues found a way to reduce hydrogen. They pressed small samples of iron (representing the core) and hydrous silicate glass (representing Earth’s early magma ocean) between diamond anvils, heated the samples to about 4,827 °C (about 8,720 °F) and squeezed them at a pressure of 111 gigapascals.
The team then transformed these already tiny samples into needles with points just 20 nanometers across 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 clump together within iron when an Earth-like planet forms. These ratios allowed Huang and his colleagues to estimate the amount of hydrogen present in the core; They estimate that the element represents between 0.07 and 0.36 percent of the core by weight. This means that the water in nine to 45 oceans contains equal amounts of hydrogen.
Schlichting says this amount of hydrogen in the core could have arisen during Earth’s early formation, adding to work from his group and others now pointing to the same conclusion. This means the water cycle has played a role on our planet ever since the core began to cool and the hydrogen, silicon and oxygen inside it began to crystallize about 4.5 billion years ago, Huang says.
This crystallization would have created convection in the core, he says, which “would have provided the driving force for an ancient geodynamo to generate Earth’s magnetic field, which is indispensable for Earth to evolve as a habitable place.”
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