The earth's primary productivity was essentially aquatic before the mid-Devonian expansion of a vascular plant biomass. As organic carbon, nitrogen, and phosphorus were retained on land, the abundant phytoplankton was adversely affected. When nutrients that were utilized, buried, and not recycled exceeded the amount newly added, the early Paleozoic phytoplankton that were adapted to a high nutrient level either disappeared or greatly declined in importance.

The late Paleozoic fern-lycopsid-arthrophyte flora produced a second major land biomass increase. Organic carbon and nutrients were locked in the black shales and coals, and marine productivity remained low. After the Permo-Triassic regression, coastal swamps no longer bordered the Pangean supercontinent, so less organic carbon was buried and more was released into the surrounding seas. Coccolithophores and dinoflagellates diversified and marine productivity expanded in the Jurassic and Cretaceous, reinforced by the new siliceous phytoplankton (diatoms, silicoflagellates, chrysomonads). As mid-Cretaceous expansion of the deciduous angiosperms raised the carbon and nutrient content of the soils, their seaward transport decreased and marine productivity dropped catastrophically in lates Cretaceous time. After a renewed Paleogene expansion, the warm-water plankton again declined, and diatoms inhabiting the colder nutrient-rich upwelling waters became the dominant Neogene producers.

High productivity, reflected in carbon isotope ratios and petroleum deposits, was attained by those microfloras best utilizing contemporaneous nutrient levels. When successive land floras rapidly sequestered increased amounts of organic carbon and nutrients in biomass, soil, and sediments, the accumulations of land-derived organic detritus coincided with nutrient shortages in the seas and phytoplankton and marine productivity declined.

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