Wednesday, Oct. 27, 2010
Something extraordinary happened to life on Earth some 740 million years ago and Utah State University geologists are exploring the tiniest — and some of the world’s oldest — fossils to find out why.
Deep in the fine-grained mudstone of eastern Utah’s Uinta Mountains, doctoral student Dawn Hayes and faculty mentor Carol Dehler have recovered evidence of Bavlinella, a bacterium that “bloomed like crazy,” depleted an already stressed environment of oxygen, crowded out more complex organisms and resulted in widespread die-off of early plant and animal life.
Hayes and Dehler are among more than a dozen USU scientists set to present their research findings at the 122nd annual meeting of the Geological Society of America Oct. 31-Nov. 3 in Denver.
“Similar evidence found in the rock record in other areas of the world implies some sort of global phenomenon rather than a localized event,” says Hayes, who completed a master’s degree from USU in spring 2010.
Did a giant meteorite strike the Earth? Did a huge volcano erupt? Or does the evidence point to gradual climate change?
“There’s no smoking gun,” says Dehler, assistant professor of sedimentology in USU’s Department of Geology. “But increased sulfur and changes in iron compounds suggest depleted oxygen in oceans, which might have been caused by bacterial blooms, along with changes in the carbon cycle that could have been due to increased volcanic activity.”
Hayes says Bavlinella is likely similar to Cyanobacteria, a modern blue-green algae that thrives in both fresh water and marine environments.
Microfossils, known as “acritarchs,” akin to those Dehler and Hayes found in the Uintas, have been discovered in the Grand Canyon. The Precambrian specimens mirror discoveries in Sweden, Greenland, Tasmania and, possibly, California’s Death Valley. In fact, it was microfossil changes found by Dehler and colleagues in rocks of the Grand Canyon that sparked Dehler and Hayes’ idea of looking for similar changes in rocks of the same age in the Uintas.
At the Uinta Mountains site, the geologists say evidence of more complex life has been discovered in rock layers beneath the Bavlinella fossils.
“There’s evidence of a eukaryotic-dominated system and the fossil record shows a distinct biotic change,” Hayes says. “This corresponds with geochemical changes in the ocean recorded during the same time period.”
Hayes and Dehler’s findings, when combined with discoveries from the Grand Canyon, suggest that widespread die-offs occurred before an intense ice age purportedly spanned the globe. According to a theory known as “Snowball Earth,” glaciers encased the planet and led to the demise of early plant and animal life.
“Snowball Earth suggests that glaciation was the cause of die-offs,” Dehler says. “We think something much earlier led to anoxia — lack of oxygen — and caused a ripple effect, enabling bacteria to flourish, further deplete the planet’s oceans of oxygen, and kill off other species.”