The layers are of quite different ages and this is not seriously disputed. The core, the Zhouyi, belongs to the Western Zhou and is usually placed around the ninth century BCE; its language, its references and its assumptions about divination all point there, and it stands at a considerable distance from the classical Chinese of the Warring States. Tradition assigns the hexagram statements to King Wen, composing in prison, and the line statements to his son the Duke of Zhou. Scholars treat these attributions as legendary and the core as accumulated diviners' record.
The Ten Wings were traditionally ascribed to Confucius. The Analects mentions the Changes only glancingly, the philosophical vocabulary of the Wings is later than his lifetime, and the consensus dates them across the Warring States and into the Han, several centuries after his death in 479 BCE. Some traditional scholars, notably Ouyang Xiu in the eleventh century, had already doubted the attribution on internal grounds.
The book owes its survival partly to being useful. When the Qin proscribed the classics in 213 BCE, the Records of the Grand Historian says works on divination, medicine and agriculture were exempt. The Changes was a working manual and passed through untouched, where the Book of Documents did not.
Manuscript evidence confirms that the text was still fluid. The silk Mawangdui copy of 168 BCE has the hexagrams in a completely different sequence from the received order, organised systematically by upper trigram, and carries commentarial material not in the standard Ten Wings, including dialogues attributed to Confucius that the received tradition never had.