Primitive Dark-Phase Cycle of Photosynthesis at the Origin of Life.

Simple phosphorylation, isomerization, and aldolisation reactions starting from glyceraldehyde have the potential to lead to the synthesis of pre-ribonucleotide polymers through a primitive form of the Calvin cycle (dark phase of photosynthesis) involving the unusual formation of phospho-nonulose phosphate and phospho-deculose phosphate, as key intermediates. These reactions involve activated phosphates which are generated from schreibersite minerals, geochemically available in Hadean times.