Which civilization is recognized as the earliest-known Mesoamerican civilization?

The Olmec civilization is recognized as the earliest-known Mesoamerican civilization due to its development in the region of present-day southern Mexico around 1200 BCE. The Olmecs are credited with laying many foundations for later cultures in Mesoamerica, including the Maya and Aztec civilizations. They established complex societies, built monumental architecture such as colossal stone heads, and developed early forms of writing and a calendar system, which influenced subsequent cultures in the region.

The other civilizations listed, such as the Maya and Aztec, emerged later in the historical timeline, building upon the achievements of the Olmecs and developing their own distinct languages, arts, and political structures. The Inca civilization, although significant in its own right, was located in South America and is therefore not considered part of Mesoamerican history. Thus, the Olmec's pioneering developments and timeline establish its prominence as the earliest civilization in Mesoamerica.