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Know the West

Ten years, 3 million pounds of soil and 1,800 sensors

The numbers behind the world’s largest weathering experiment.


The white domes and glass pyramids of Biosphere 2 rise high above the desert outside Tucson, Arizona. In the early 1990s, it housed eight people for two years as part of a notoriously failed experiment in self-sufficiency. Now it’s a research station maintained by the University of Arizona. In its second year, the largest indoor soil weathering experiment involves three million pounds of soil piled in huge mounds and sprayed regularly with water. “It’s like Groundhog Day,” says Peter Troch, science director. “You basically create the same conditions all over again, every three days.” This will go on for 10 years across three manmade hills, each peppered with more than 1,800 sensors to measure exactly where the water goes, down to the molecule.

It’s at this molecular level that minerals and water jostle and lock arms in the process of weathering, releasing nutrients like potassium and calcium from the soil. Plants then suck up those nutrients through their roots. From there, the minerals pass through the food web to other life forms, creating a livable world for humans and other organisms. The exact way that water moves through a landscape is also important: If we understand weathering patterns, which determine water quality and pollutant uptake, we’ll be better able to plan irrigation and manage drinking water in the face of climate change and water shortages in the West. Because weathering happens much faster in carefully controlled experiments at small scales than it does in the real world, it’s hard to extrapolate research data. The Biosphere 2 experiment offers replication — the three identical hills will get exactly the same treatment — at an enormous scale, which will allow scientists to see the complex processes underway on landscapes outside.