London, May 19 (ANI): In a new research, scientists have suggested that a jump in the concentration of sulphate in the world's oceans 500 million years ago was caused by mud stirred up by sea-floor animals like worms, clams and crustaceans.
During that period, known as the Cambrian explosion, something put the evolutionary pedal to the metal, and the stately, subdued pace of animal life on Earth revved up.
Alongside this spurt in speciation, came a jump in the concentration of sulphate in the world's oceans.
"It hasn't been clear why," said Don Canfield of the University of Southern Denmark in Odense.
But, Canfield and his collaborator, James Farquhar of the University of Maryland in College Park, have a theory to explain it.
According to a report in Nature News, in a new study published in the Proceedings of the National Academy of Sciences, Canfield and Farquhar attribute the rise in sulphate to the onset of bioturbidity - the burrowing, sluicing, pumping and mixing caused by masses of worms, clams, crustaceans and other animals that began to appear around this time in Earth's history.
Before these sea-floor animals began their steady churn, sulphate, arriving in seas in the run-off from rivers, would largely be turned into hydrogen sulphide by bacteria living in the ocean floor.
The sulphide would then be converted to pyrite (FeS2), which, once buried, removes the sulphate from the system.
Once bioturbation turned on, however, oxygen in the deep ocean could mix more freely with the sediments, allowing bacteria and other processes to recycle pyrite and turn it back to sulphate.
This excess sulphate would have reached a saturation point, giving rise to the formation of gypsum deposits - a mineral that, along with sulphate levels, also happened to rise in the rock record around this time.
The researchers roughly sketched changes in ocean sulphate concentrations through time by directly analyzing tiny amounts of brine trapped in salt crystals.
But these samples are few and far between, so to get a more complete timeline, the team analyzed sulphide and sulphate isotopes in thousands of ancient sedimentary rock samples.
This analysis doesn't track sulphate concentration changes directly, but shows how much of the sulphur ended up in pyrite versus gypsum.
Finally, the researchers built a simple model for the effects of bioturbation and found that its output - both in the timing and the magnitude of the sulphate signals - matched what they were seeing in the data. (ANI)