We know that most life on Earth requires oxygen for survival.
We also know that our planet's atmosphere did not always contain this necessary substance on which our life has evolved into further complexity.
One of the greatest questions in studying the origins of life is to understand how and when oxygenic photosynthesis first began.

ELSI PI Joseph Kirschvink and team test the hypothesis that manganese-based photosynthesis, a chemical reaction that does not have to involve oxygen, occurred prior to the evolution of the oxygen-releasing cyanobacteria, and demonstrate that manganese-oxidizing photosynthesis was a stepping-stone for oxygen-producing, water-splitting photosynthesis.

Here is the link to the article "Manganese-oxidizing photosynthesis before the rise of cyanobacteria" co-authored by Joseph Kirschvink, published June 24, 2013 in the Proceedings of the National Academy of Sciences.

Journal: Proceedings of the National Academy of Sciences of the United States of America（PNAS）

Article title: "Manganese-oxidizing photosynthesis before the rise of cyanobacteria"

Authors: Jena E. Johnson, Samuel M. Webb, Katherine Thomas, Shuhei Ono, Joseph L. Kirschvink, and Woodward W. Fischer

DOI: 10.1073/pnas.1305530110

Link: http://www.pnas.org/content/early/2013/06/20/1305530110.full.pdf+html (PNAS)

http://www.caltech.edu/content/stepping-stone-oxygen-earth (Caltech)