Two geoscientists, one with Princeton University, the other with Guangzhou Institute of Geochemistry, have developed a theory to explain how helium-3 leaks from the Earth's core into the mantle. In their study, reported in the journal Nature Geoscience, Jie Deng and Zhixue Du used first-principle calculations to show that helium-3 could enter magnesium oxide at the core-mantle boundary, allowing its entry into the mantle.