A few years ago, on a ranch in the small Marin town of Nicasio, a series of events led to an important environmental discovery. Scientists found that a single application of compost on rangeland helps plants suck carbon from the air and store it in the ground. Compost on less than three acres can offset carbon emissions from four diesel truck trips from San Francisco to Washington, D.C. If compost were applied to the millions of acres of rangeland in California, the effect would be monumental.