How and why did atmospheric carbon dioxide concentrations change over the Phanerozoic eon?

We use paleosols to reconstruct ancient atmospheric carbon dioxide concentrations. You can read about how this proxy works and the primary uncertainties associated with it in a Geochemical News article.

Currently this work involves reducing the uncertainty associated with these reconstructions and interpreting paleosol-based records. Current focus is on the Pliocene (Shaanxi, China and Teruel, Spain) and the Paleocene-Eocene Thermal Maximum (Wyoming, USA).

The Pliocene Red Clay near Yulin, Shaanxi Province, China

Pliocene red beds near Teruel, Spain

Bighorn Basin, Wyoming, USA