What is the oldest known civilization?

Context: Scholars generally acknowledge six cradles of civilization. Mesopotamia, Ancient Egypt, Indus Valley, and Ancient China are believed to be the earliest in the Old World. Cradles of civilization in the New World are the Caral-Supe civilization of coastal Peru and the Olmec civilization of Mexico. All of the cradles of civilization depended upon agriculture for sustenance. All depended upon farmers producing an agricultural surplus to support the centralized government, political leaders, priests, and public works of the urban centers of the civilization.

Less formally, the term "cradle of civilization" is often used to refer to other historic ancient civilizations, such as Greece or Rome, which have both been called the "cradle of Western civilization".

Answer: The oldest known human civilizations are known to exist in Mesopotamia (Modern day Iraq), Indus Valley (a region located in modern-day Pakistan), Ancient Egypt and Ancient China.