It's Complicated "Recent geochemical evidence indicates that, at least locally, ferruginous (iron rich) or even sulphidic (sulfur rich) conditions persisted through the Ediacaran period, long after the Great Oxygenation Event," Fike says.
"Things are much more complicated than we had supposed."
"As a community, we don't have a good sense of the spatial variation of these zones within different bodies of water, " says Fike.
"What's more, different assessments can arise from the interpretation of different geochemical proxies, from physical separation between different ocean basins, or from the reworking of sediments after deposition," he continues.
The underlying problem is a low sampling rate. "As we try to unravel these changes in Earth's history, " Fike says, "we often don't have 100 different places where we can measure rocks of the same age. We're stuck with a few samples, and the natural tendency is to take your rocks and extrapolate."
The only way "to wring order from the chaos," Fike says, is to develop a full three-dimensional model of the Earth that has enough spatial resolution to wash out bad data.
Mystery of the vanishing acritarchs "If you map out redox proxies in enough spatial detail, you can tell a beautiful, consistent story that relates environmental change to the paleontological record," Fike says.
To illustrate, he tells the story of a group of spiny acritarchs, microfossils found in the one of the oldest fossil beds on Earth, the Doushantuo formation in south China.
Nobody was really sure what the acritarchs were. Some people thought they were green algae. Others thought they might be dinoflagellates that had evolved spines to avoid predation by animals.
"Scientists looking at the Doushantuo thought they understood what they were seeing," Fike says. "Oxygen is appearing, the acritarchs are evolving, and this is the start of the b
|Contact: Diana Lutz|
Washington University in St. Louis