Waterfall Slime

*Discoidea pneumakatechon*. A pendulous slime of simple eukaryote cells which has expelled its own ability to breathe.

1. Sulfide stress A drop in oxygen levels and a rise in hydrogen sulfide has caused the slime to abandon oxygen-breathing life and return to a slower sulfur-based metabolism.

2. Mitochondrial background In complex Earth life, hydrogen sulfide poisons the cellular powerhouses called mitochondria. Most Protean cells have similar oxygen-burning compartments, though their origin is unknown. The cells of the waterfall slime have destroyed these compartments, accepting a 94% drop in metabolic efficiency in order to survive deoxygenation.

3. Sulfide source Hydrogen sulfide is produced by the decomposition of biomatter in oxygen-poor water. The waterfall slime's sulfur tolerance makes it a good indicator of mass death elsewhere in the biosphere.

Assessment: a poor sign for the long term survival of Protean oceans. Rising hydrogen sulfide levels after ocean deoxygenation played a role in Earth's Permian Extinction, which wiped out 95% of species on Earth.