Roland Piquepaille writes "To celebrate Earth Day, the NASA Earth Observatory recently revealed global measurements of the Earth's metabolism. 'Combining space-based measurements of a range of plant properties collected by the Moderate Resolution Imaging Spectroradiometer (MODIS) with a suite of other satellite and surface-based measurements, NASA scientists produce composite maps of our world's 'net primary production' every 8 days. This new measurement is called net production because it indicates how much carbon dioxide is taken in by vegetation during photosynthesis minus how much is given off during respiration.' Check this column for a summary including the usefulness of such measurements. You'll also find maps showing the seasonal variation of Earth's net primary production."