Thomas Chrowder Chamberlin (1843 – 1928) was an American geophysicist. He worked for the US Geological Survey and later was president of the University of Wisconsin (1887 – 1892), and a professor at the University of Chicago (1892 – 1918).
He developed the planetesimal theory, which states that Earth was made from smaller objects that gradually built the planets by accretion. From this theory and other geological evidence he concluded that Earth was much older than assumed by Lord Kelvin (ca 100 million years) at the time.
In 1893 he founded the Journal of Geology. A crater on Mars is named in his honor.