Earth's ancient oceans held much lower concentrations of sulfate -- a key biological nutrient¹ -- than previously² recognized, according to research published this week in Science. The findings paint a new portrait of our planet's early biosphere³ and primitive⁴ marine⁵ life. Organisms require sulfur⁶ as a nutrient, and it plays a central role in regulating atmospheric⁷ chemistry and global climate.

 

"Our findings are a fraction of previous estimates, and thousands of time lower than current seawater levels," says Sean Crowe, a lead author of the study and an assistant professor in the Departments of Microbiology and Immunology, and Earth, Ocean and Atmospheric Sciences at the University of British Columbia.

 

"At these trace amounts, sulfate would have been poorly mixed and short-lived in the oceans -- and this sulfate scarcity⁸ would have shaped the nature, activity and evolution of early life on Earth."

 

UBC, University of Southern Denmark, CalTech, University of Minnesota Duluth, and University of Maryland researchers used new techniques and models to calibrate⁹ fingerprints¹⁰ of bacterial¹¹ sulfur metabolisms¹² in Lake Matano, Indonesia -- a modern lake with chemistry similar to Earth's early oceans.

 

Measuring these fingerprints in rocks older than 2.5 billion years, they discovered sulfate 80 times lower than previously thought.

 

The more sensitive fingerprinting¹³ provides a powerful tool to search for sulfur metabolisms deep in Earth's history or on other planets like Mars.

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