Introduction

How oxygen levels in Earth's atmosphere and oceans evolved has always been a central question in Earth System Science. Researchers have developed numerous tracers to tackle this question, utilizing geochemical characteristics of different elements.

Iodine as a Proxy

Iodine incorporated in calcium carbonate (including biogenic) minerals, reported as I/Ca, is a proxy for dissolved oxygen in seawater.

Review and Future Directions

Here we review the rationale behind this proxy, its recent applications and some potential future research directions.