EARTH × LIFE

The Largest Carbon Swing Ever Recorded

~574 to 567 million years ago

Proterozoic · Neoproterozoic · Ediacaran

Between the Gaskiers glaciation and the arrival of large Ediacaran fossils, carbonate rock on four continents records the carbon in seawater turning lighter by some twelve parts per thousand, a deeper dive than anything in the entire animal fossil record that followed. Geologists call it the Shuram excursion, and thirty years of argument have not settled whether it happened in the ocean or in the rock.

Why it matters

If the signal is primary, the ocean was rebuilding its carbon and oxygen budgets at exactly the moment animals grew large, and one of the most cited explanations for that timing holds. If it was written into the rock long after burial, the explanation goes with it. The most recent work in Oman finds real alteration, four kinds of it, but nowhere near enough to account for the swing, which leaves at least part of the signal in the water.

Dating & uncertaintyDisputed

Dated between about 574 and 567 Ma in Oman and Death Valley, and between 571 and 562 Ma where it is tied to the Chinese and Tarim sections. Three causes compete: a genuine upheaval in the ocean carbon cycle, alteration of the rock long after burial, or volcanic ash made from recycled seafloor limestone.

Sources

1. Busch et al. (2022), Earth and Planetary Science Letters · Global and local drivers of the Ediacaran Shuram carbon isotope excursion
2. Bergmann et al. (2025), Geochemistry, Geophysics, Geosystems · Origins and alteration of Ediacaran carbonates recording the Shuram excursion in Oman
3. Liu et al. (2021), Science Bulletin · The largest negative carbon isotope excursions in Neoproterozoic carbonates caused by recycled carbonatite volcanic ash

Earth history as one day

20:57:563 h 2 min before midnight

if Earth’s 4.54 billion years were compressed into a single day