According to Hinduism, as there are four seasons in a year, there are four Yugas namely Satya-Yuga, Treta-Yuga, Dvapara-Yuga, Kali-Yuga. At the end of a full cycle of four Yugas, the life on the earth comes to an end (though not completely) and a new era starts. The humanity enters into a new era. The present era is known as Kali-Yuga i.e. Dark Age.