Molybdenum-dependent nitrogenase catalyzes the conversion of atmospheric nitrogen (N2) into ammonia (NH3), a process involving the transfer of 8 electrons and 8 protons to the catalytic cofactor (FeMo-co). FeMo-co is an iron-sulfur cluster containing 7 Fe atoms, 1 Mo atom, and 9 S atoms. The reaction mechanism proceeds through a series of intermediates, E0 to E8, each corresponding to the progressive addition of electrons. Experimental evidence indicates that the enzyme needs to accumulate 4 electrons and 4 protons at the E4 state before binding N2. It is widely accepted that these electrons and protons are stored as hydride ions bound to the Fe atoms. These hydrides undergo reductive elimination of H2, which facilitates the binding of N2. However, the structure and dynamics of the E4 state of FeMo-co remain subjects of considerable debate. In this talk, I will discuss the thermal dynamics of hydrogen atoms in the E4 state, as obtained from multiscale modeling of nitrogenase. I will show that the E4 state is highly fluxional, with hydrides and protons visiting multiple limiting configurations. I will also address the heritability of sulfur atoms bridging the Fe atoms on the reactive edge of the FeMo-co bond and how it may transiently dissociate as H2S under turnover.