The rare earth element distribution in marine carbonates as a potential proxy for seawater pH on early earth

Understanding the marine environment of early Earth is crucial for understanding the evolution of climate and early life. However, the master variable of Archean and Proterozoic seawater, the pH, is poorly constrained, and published ideas about the pH range encompass ~7 pH units from mildly acidic to hyperalkaline. To better infer ancient seawater pH, we examine the possibility of a seawater pH proxy using rare earth elements (REEs) in marine carbonates. The principle is based on increasing concentrations of heavy rare earth elements in solution relative to the light REEs with decreasing pH due to REE complexation and scavenging. We calibrated such an REE pH proxy using pH variability in modern seawater and tested the proxy with ~100 REE measurements from 13 separate carbonate formations. We compared our pH estimates derived from the REE proxy to published pH estimates of Cenozoic and Neoproterozoic seawater that use the established pH proxy of boron isotopes (δ11B). REE-pH estimates ag..., , , # The Rare Earth Element Distribution in Marine Carbonates as a Potential Proxy for Seawater pH on Early Earth

[https://doi.org/10.5061/dryad.69p8cz99r](https://doi.org/10.5061/dryad.69p8cz99r)

## Data and file structure

There are two CSVs and two URLs for supplementary data for Lin and Catling (2024). 

### Supplementary Tables

Supplementary Table 1: Rare earth element (REE) speciation using the PHREEQC model mentioned in the manuscript. The labels on the data include the pH and REE species. Please refer to the PHREEQC source code mentioned in Supplementary Data below for more instructions on generating the table.

Supplementary Table 2: REE slope and pH estimates of marine carbonate formations mentioned in the manuscript. Data includes the formations, sample label, epoch or period, pH with uncertainty, REE slope with uncertainty, and references.

### Supplementary Data

[](https://doi.org/10.2475/001c.118215)

The supplem...