Kalpa (aeon)
Kalpa (Sanskrit: कल्प kalpa) is a Sanskrit word meaning an aeon, or a relatively long period of time (by human calculation) in Hindu and Buddhist cosmology. The concept is first mentioned in the Mahabharata.
Romila Thapar holds that "the kalpa is first referred to in the inscriptions of Asoka". In the Pali (= early Buddhist) form the word kappa is mentioned in the assumed oldest scripture of Buddhism, the Sutta Nipata, where it speaks of "Kappâtita: one who has gone beyond time, an Arahant". This part of the Buddhist manuscripts dates back to the middle part of the last millennium BC.
Generally speaking, a kalpa is the period of time between the creation and recreation of a world or universe. The definition of a kalpa equaling 4.32 billion years is found in the Puranas—specifically Vishnu Purana and Bhagavata Purana.
Buddhism
According to Visuddhimagga, there are several explanations for types of kalpas and their duration. In the first explanation, there are four types:
Ayu-Kalpa - a variable time span representing the life expectancy of a typical human being in a particular era or yuga. This can be as high as one asankya or as small as 10 years. This number is directly proportional to the level of virtue of people in that era. Currently this value hovers around 100 years and is continually decreasing.
