Understanding the resource potential of natural hydrogen on Earth: Scientific gaps, uncertainties and recommendations - Etiope, Giuseppe; Ellis, Geoffrey; Ardakani, Omid; Boreham, Christopher; Klitzke, Peter; Martín-Monge, Antonio; Reis, Humberto; Templeton, Alexis; Kim, Hyeong; Gaucher, Eric; Sissmann, Olivier (Earth-Science Reviews, 2026)