The most abundant photosynthetic thing was missed until 1988

Prochlorococcus is a cyanobacterium smaller than a micrometre, and it is the most numerous photosynthetic cell in the ocean. It was described in 1988 because it slipped through the nets.

The usual way to catch marine microbes was a filter, and this cell passed through. Flow cytometry, counting cells by the light they scatter and the pigments they fluoresce, found an abundant prochlorophyte in the open ocean’s sunlit layer. Sally Chisholm and colleagues published it in 1988. It is now understood to be the most abundant photosynthetic organism on the planet, present by the million in a millilitre of clear tropical seawater where a net comes up empty.

How much of the Earth’s photosynthesis it does depends on the ledger. Estimates for its share of marine primary production run from a few percent to around a fifth. What does not move is the abundance, or the embarrassment: the organism that runs a noticeable fraction of the planet’s carbon fixation was invisible to biology until the instrument changed. The oxygen you are using is partly its work, and partly everyone else’s, and the split is the soft number.