Who theorized that Earth and objects on it were in constant motion around the Sun?

The correct answer is rooted in the revolutionary ideas brought forth by Copernicus, who proposed the heliocentric model of the solar system. This model placed the Sun, rather than the Earth, at the center and suggested that all planets, including Earth, revolve around it. This was a significant departure from the geocentric view that had dominated for centuries, where the Earth was considered the center of the universe and all celestial bodies moved around it.

Copernicus's ideas laid the groundwork for modern astronomy and challenged long-held beliefs about the universe's structure. His theories indicated not only that the Earth was in constant motion—rotating on its axis and orbiting the Sun—but also brought about a paradigm shift in how humans perceived their place in the cosmos. This pivotal moment in science set the stage for later astronomers, like Galileo, Kepler, and Newton, to build upon and refine these concepts, but it was Copernicus who first articulated this revolutionary perspective.