Why lithium? The Missing Ocean Mineral conjecture: a possible Ediacaran origin for neural lithium function.

We propose the Missing Ocean Mineral (MOM) conjecture that lithium, through competitionwith magnesium at the catalytic sites of regulatory enzymes, originally functioned as astochastic environmental interrupt — a low-frequency signal that allowed early eukaryoticcells to pause high-priority processes and permit periodic maintenance. Acute depletion ofocean lithium following the Marinoan glaciation (~635 Mya) disrupted this ambientregulation and would have imposed selection pressure for internal lithium retention andcontrol. The metazoan lineages that survived this crisis could have evolved mechanisms toretain, regulate, and release lithium on demand; converting an unreliable environmental signalinto a controllable intracellular one. This innovation may in turn have prompted the evolutionof the metazoan neuron: a cell type whose defining capacity for controlled state-switchingwould have derived from the internalisation of an ancestral lithium-based interrupt.