Why does the Precambrian end in 540 million years?

The Precambrian era ends around 540 million years ago with the onset of the Cambrian period, marked by a significant increase in the diversity of life forms known as the "Cambrian Explosion." This era saw the first appearance of complex, multicellular organisms and the development of hard body parts, which left a more complete fossil record. The transition signifies a major evolutionary milestone, leading to the proliferation of various life forms and the establishment of modern ecosystems.