Non-linear frequency-doubling up-conversion in sulfide minerals enables deep-sea oxygenic photosynthesis.

Visible light emission exceeding purely thermal radiation has been imaged at deep-sea hydrothermal vents, yet the underlying mechanisms remain unexplained. Here, we show that visible light can be produced from geothermal infrared radiation via nonlinear frequency-doubling up-conversion in sulfide minerals that are abundant in hydrothermal vents. Chalcopyrite exhibits significant second harmonic generation, which is further amplified under high pressure, yielding a 400-700 nm photon flux three orders of magnitude greater than blackbody emission. When exposed to 1064 nm of irradiation, chalcopyrite induces fluorescence responses in the cyanobacterium sp. PCC 7002 at 656 and 685 nm, suggesting that the up-converted 532 nm light is absorbed by phycobilisomes and transferred to photosystem II. Metagenomic analysis reveals a strong correlation between cyanobacteria and high-temperature, chalcopyrite-rich vents. Similar up-conversion processes have also been observed in other sulfide minerals, emitting wavelengths covering the entire visible spectrum. These findings unveil a novel mineral-mediated photonic mechanism that generates biologically relevant visible light at hydrothermal vents, which can be harnessed by oxygenic photosynthetic cyanobacteria in Earth's deep biosphere and possibly beyond.