Lord Sri Krishna made an earthly appearance in roughly 3220 B.C., and He left this planet in 3102 B.C. However, because He is the Supreme Personality of Godhead, the cause of all causes, He is eternally existing. Therefore these dates are simply a recording of His incarnation in Dvapara-yuga (the age prior to the present Age of Kali). He spoke the Bhagavad-gita to Arjuna in Dvapara-yuga, but this does not limit His position as the adi-purusha (the original Supreme Person) and the adi-guru (the original teacher). In the Vedic literature Lord Krishna is described as the ultimate source of all knowledge; hence, He is the most reliable source of knowledge. The whole guru-parampara—the disciplic succession—begins with Him because He is the original preceptor.