The ancient Greek Aristotle (384 BC–322 BC) wrote in his "Meteorology" of how the earth had the potential for physical change, including the belief that all rivers and seas at one time did not exist where they were, and were dry. The Greek writer Xenophanes (570 BC–480 BC) wrote of how inland marine fossils were evidence that massive periodic flooding had wiped out mankind several times in the past, but never wrote of land formation or shifting seashores. Du Yu (222–285) a Chinese Jin Dynasty officer, believed that the land of hills would eventually be leveled into valleys and valleys would gradually rise to form hills. The Daoist alchemist Ge Hong (284–364) wrote of the legendary immortal Magu; in a written dialogue by Ge, Ma Gu described how what was once the Eastern Sea (i.e. East China Sea) had transformed into solid land where mulberry trees grew, and would one day be filled with mountains and dry, dusty lands. The later Persian Muslim scholar Abū Rayhān al-Bīrūnī (973–1048) hypothesized that India was once covered by the Indian Ocean while observing rock formations at the mouths of rivers.