All the same, understanding the processes that made the rock is what he and Whitehouse set out to do. They observed that some of the bands in the rock formation show irregular variations in their thickness, so that they look like chains of meaty sausages attached by more narrow links. Sedimentation doesn't produce that sort of pattern. These bands do not have a sedimentary origin, says Fedo.
Rock Bands Reinterpreted
Rather, says Fedo, we think the green bands are igneous. Igneous rock, unlike sedimentary rock, comes from volcanic activity. If the banded rocks are igneous, the Akilia rocks may well have formed in the absence of life-sustaining oceans, making them much less likely to have harbored early life.
"They've become banded because these rocks are extremely deformed" by the intense heat and pressure beneath the Earth's crust, says Fedo.
As for the evidence from the graphite, Fedo cautions against jumping to conclusions. "There are non-biological mechanisms that are capable of producing carbon that is very light, that mimics the values that living things generate," he says.
So if the banded rock isn't a product of sedimentation, what is it? Fedo thinks the green, iron-rich igneous rock formed first, in the aftermath of a volcano, but that later cracks filled with heated water carrying dissolved minerals. Those minerals stuck in the cracks and hardened into veins of white quartz.
Meanwhile, Mojzsis stands by his interpretation of the data with its older date. The geological picture is extremely complicated, he says, expressing concern that Fedo and Whitehouse may have oversimplified data in the process of their analysis.
Fedo acknowledges that the new interpretation is controversial, and the true age of life on Earth is bound to be contested for some time.
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