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Redox Reactions

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Oxidation-reduction or redox reactions involve the transfer of electrons from one molecule or atom to another. When an atom gains an electron, another atom must lose an electron, meaning oxidation and reduction must occur together. Since the redox occurs in pairs, the atom that gets oxidized is also called the reducing agent or reductant, and the atom that is reduced is also called the oxidizing agent or oxidant. A straightforward way to remember the definitions of oxidation and reduction is...

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Redox Equilibria: Overview

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A reduction-oxidation reaction is commonly called a redox reaction. In a redox reaction, electrons are transferred from one species to another rather than being shared between or among atoms. The reducing agent or reductant is the species that loses electrons and gets oxidized in the process. The species that gains electrons and gets reduced in the process is the oxidizing agent or oxidant. Redox reactions are represented as two separate equations called half-reactions, where one equation...

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Related Experiment Video

Updated: May 23, 2026

EPR Monitored Redox Titration of the Cofactors of Saccharomyces cerevisiae Nar1

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Published on: November 26, 2014

The carbon cycle and associated redox processes through time.

John M Hayes¹, Jacob R Waldbauer

¹Woods Hole Oceanographic Institution, Department of Geology and Geophysics, Woods Hole, MA 02543, USA. jhayes@whoi.edu

Philosophical Transactions of the Royal Society of London. Series B, Biological Sciences

|June 7, 2006

Summary

This summary is machine-generated.

The carbon cycle releases oxidizing power, primarily as Fe3+ and sulfate, not O2. Elevated 13C in ancient carbonates suggests methanogenic bacteria, not organic carbon burial, drove this process.

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Area of Science:

Geochemistry
Biogeochemistry
Early Earth conditions

Background:

Earth's carbon cycle involves limestone and organic material deposition.
Biologically catalyzed redox reactions involving H, S, Fe, and O are central.
Carbon isotope variations (13C) in sediments track these reactions.

Purpose of the Study:

Reconstruct Earth's biogeochemical carbon cycle.
Investigate the source of oxidizing power accumulation.
Interpret 13C records in ancient carbonate minerals.

Main Methods:

Analysis of 13C variations in sedimentary carbonate and organic materials.
Reconstruction of redox reactions using geochemical proxies.
Mass balance calculations for oxidizing power.

Main Results:

The carbon cycle continuously releases oxidizing power, mainly as Fe3+ and sulfate.
Atmospheric O2 and dissolved O2 represent less than 3% of total oxidizing power since 3.8 Gyr ago.
Elevated 13C in ~2.3 Gyr old carbonates indicates methanogenic bacteria activity.

Conclusions:

Methanogenic bacteria in sediments played a significant role in the early carbon cycle.
Interpreting 13C records requires considering biological processes beyond organic carbon burial.
Oxidizing power accumulation is primarily linked to Fe3+ and sulfate, with O2 being a minor component.