American geologist and authority on soils who worked closely with experts from many countries to develop international classification systems for soil materials.

After earning a B.S. from the University of Missouri in 1889, Marbut worked for the Missouri Geological Survey before doing graduate work in geology and physiography at Harvard University and in Europe. He returned to the University of Missouri, where he taught from 1895 to 1910, becoming increasingly interested in the composition of soils. In 1910 he was appointed chief of the Soil Survey of the U.S. Department of Agriculture, which mapped the soils of the country. He translated into English the German edition of a pioneering Russian work, The Great Soil Groups of the World and Their Development (1927), and wrote a basic text, Soils of the U.S. (1935). He was about to begin a preliminary study of the soils of China when he died of pneumonia.