What is Buddhist unit of Kalpa?

Kalpa - Periodic manifestations and dissolutions of Universes, which go on eternally. Great kalpas consist of four asamkhiya kalpas corresponding to childhood. maturity, old age and the death of the universe. In each Kalpa there are times when one, two, three or five Buddha’s are said to appear and there are times when no Buddha will appear. Our present Kalpa is Bhadra Kalpa where five Buddha’s are predicted to appear. In Kassapa Buddha era, the human life span was 3,000 years, in this present era (Gotama Buddha era) it was 100 years and in Mettreyya Buddha’s era it will be 80,000 years. WE knew that the world is evolving and continue on this way for eternally.