Now You Know

Monday, February 21, 2005 | 12:00 a.m. CST; updated 11:27 p.m. CDT, Saturday, July 19, 2008

Ocean sulfate levels

What was learned: A team of geologists, including former MU professor of geological science Tim Lyons, developed a method for estimating sulfate levels in ancient oceans as a way to measure oxygen concentrations in the atmosphere at the same time.

How they did it: Lyons, who now teaches at the University of California-Riverside, and two researchers looked at sulfate in 1.7 billion-,

1.5 billion- and 1.2 billion-year-old ocean sediments preserved in limestone. They then tested the sulfate for sulfur isotopes — atoms of the same element with a differing numbers of neutrons in the nucleus.

The team noted the changes in the sulfate’s isotopic composition over time. As shown in their tests, the older seawater contained more rapid variability in its isotopes than compared to today. The high isotopic variability in the past shows low levels of sulfate and oxygen.

Why it matters: By measuring the amount of sulfate in seawater, researchers can estimate how much oxygen was present in the atmosphere years ago and then test how quickly the oxygen accumulated over time. This would help scientists develop a better timeline to the evolutionary process that led to many multicellular plants and animals.

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