Mackinawite and greigite in ancient alkaline hydrothermal chimneys: Identifying potential key catalysts for emergent life

- We use Raman Spectroscopy to study ancient hydrothermal iron sulfide formation <100 °C.
- We show hydrothermal formation of mackinawite and greigite iron sulfide phases.
- Greigite is observed at 70-75 °C under anoxic conditions.
- We suggest a FeIII-mackinawite intermediate in the mackinawite-greigite transition.
- Mackinawite is suggested as the dominant catalyst in ancient pre-biotic chemistry.