Ancient oceans were starved of key nutrient

The Earth's ancient oceans held much lower concentrations of sulphate - a key biological nutrient - than previously recognised, according to a new research.
The findings paint a new portrait of our planet's early biosphere and primitive marine life.
Organisms require sulphur as a nutrient, and it plays a central role in regulating atmospheric chemistry and global climate.
"Our findings are a fraction of previous estimates, and thousands of time lower than current seawater levels," said Sean Crowe, a lead author of the study, from the University of British Columbia.
"At these trace amounts, sulfate would have been poorly mixed and short-lived in the oceans - and this sulfate scarcity would have shaped the nature, activity and evolution of early life on Earth," said Crowe.

Researchers used new techniques and models to calibrate fingerprints of bacterial sulphur metabolisms 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 fingerprinting provides a powerful tool to search for sulphur metabolisms deep in Earth's history or on other planets like Mars.
Previous research has suggested that Archean sulfate levels were as low as 200 micromolar - concentrations at which sulphur would still have been abundantly available to early marine life.
The new results indicate levels were likely less than 2.5 micromolar, thousands of times lower than today.

Researchers used state-of-the-art mass spectrometric approaches to demonstrate that microorganisms fractionate sulphur isotopes at concentrations orders of magnitude lower than previously recognised.
They found that microbial sulphur metabolisms impart large fingerprints even when sulfate is scarce.
The study was published in the journal Science.