Correction.
In Charles Mann's News Profile "Lynn Margulis: Science's unruly Mother Earth" (19 Apr., p. 378), the illustration on page 379 should have been credited to Walter Shearer, in Scientists on Gaia, S. Schneider and P. Boston, Eds. (MIT Press, Cambridge, MA, in press), based on measurements and observations of Russell Schnell, L. R. Maki, G. Vali, and their colleagues.