During photosynthesis, the chlorophyll in healthy plants absorbs light to be converted into energy, but it also emits a little bit of light that's not visible to the human eye. Scientists have now figured out how to use that fluorescent glow to measure the productivity of plants in a given region.

Using existing data from satellites designed for entirely different purposes, such as ozone monitoring, NASA scientists were able to show that during the Northern Hemisphere's growing season, the midwestern U.S. has more photosynthetic activity than anywhere else on the planet, including the Amazon (the tropics are more productive on a yearly basis, however). Nearly all of this can be attributed to agriculture in what is sometimes called America's Corn Belt – where, unlike the rainforest, crops are bred, engineered, and managed to be as productive as possible.

The image above is a compilation of data collected each early July from 2007 to 2011. The scientists think that fluorescence is a better measure of agricultural activity than anything currently used. And when they compared their results against ground measurements of carbon flux and yield statistics, they checked out.