The late Precambrian greening of the Earth

The Precambrian: a green alternative Dozens of studies in the past decade have reported carbon isotope variations in Neoproterozoic carbonate rocks and linked them to perturbations of the global carbon cycle. Paul Knauth and Martin Kennedy have taken a sideways look at the data by concentrating on the oxygen isotope measurements (for over 20,000 samples) that are necessarily obtained as part of the carbon isotope analysis but are often overlooked. They arrive at the striking conclusion that the combined oxygen and carbon isotope systematics are identical to those of well-understood Phanerozoic examples that lithified in coastal pore fluids receiving a groundwater influx of photosynthetic carbon from terrestrial phytomass. Rather than being perturbations to the carbon cycle, widely reported decreases in 13C/12C in Neoproterozoic carbonates are more easily interpreted by analogy to the Phanerozoic examples. And that could suggest a 'greening' of the Earth under a ground-hugging mat of photosynthetic algae, mosses and fungi in the late Precambrian. Such an event, producing oxygen and phytomass, could even be indirectly responsible for the critical transition from the essentially microbial world of the Precambrian to the metazoan world of the Cambrian.