Tiny Iron Oxide Stones Reveal Ancient Oceans Held Less Organic Carbon Than Thought

Geologists have analyzed tiny, spherical iron oxide stones called ooids, which act as micro-reservoirs of ancient carbon, to reconstruct the chemistry of Earth’s primordial oceans. The data suggests that between 1,000 and 541 million years ago, the oceans held significantly less organic carbon than current models predicted.

The ooids trapped carbon isotopes from the seawater as they formed, providing a precise chemical snapshot of the distant past. This finding indicates that the early marine carbon cycle operated under different conditions, which has implications for understanding the major environmental shifts that preceded and enabled the subsequent rise and diversification of complex life.