C. The Earth was not the center of the universe.
Copernicus proposed a heliocentric model of the solar system, in which the Sun, not the Earth, was at the center of the universe. This theory challenged the prevailing geocentric model, which held that the Earth was at the center of the universe, and was supported by observations of the planets' movements that were difficult to explain under the geocentric model. Copernicus' theory was controversial, as it contradicted the biblical teachings and the Catholic Church's dogma at the time, and was not fully accepted until later.