Shields, Graham A. (2016) Earth system transition during the Tonian–Cambrian interval of biological innovation: nutrients, climate, oxygen and the marine organic carbon capacitor. In: Earth System Evolution and Early Life: a Celebration of the Work of Martin Brasier. . Geological Society Special Publications, 448 . Geological Society, London, pp. 1-17. DOI 10.1144/SP448.17.

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Abstract

The Tonian–Cambrian interval (c. 0.9–0.5 Ga) witnessed major tectonic, climatic and
chemical changes to the Earth system and culminated in the Ediacaran–Cambrian radiation of animals.
Negative carbon isotope (d13C) excursions of extraordinary magnitude form the backdrop to
all these events and are consistent with the presence of a vast marine organic carbon reservoir that
changed its size due to periodic imbalances between organic production (as an oxidant source) and
terrestrial oxidant sinks. Prior to both Cryogenian glaciations, this pool of long-lived organic carbon
may have become substantially depleted, leading to a weakening of the regulation of climate
and oxygen. The late Ediacaran Shuram anomaly probably represents a third depletion event,
which was followed by oxygenation and the Ediacaran–Cambrian radiation. The evolutionary
diversification of animals shortened the ocean residence time of organic carbon and introduced
new carbon cycle feedbacks that together helped to mould the modern Earth system.

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