Nature turns through different seasons, spring, summer, autumn, winter. This universe also turns through seasons known as ages: Satya, Treta, Dvapara, and Kali. From creation to destruction, this universe exists in our earth's time for more than three hundred trillion years, which is but one breath of Lord Maha Vishnu. Lord Maha Vishnu lies upon the causal ocean, deep in his own mystic slumber. Like bubbles in a cosmic ocean, countless universes rise and are destroyed each time the blessed Lord breathes in and out.
The golden age of Satya yuga is clean and pure. Then, like summer and autumn, the Treta and Dvapara yugas begin, and with their passing, truth, and purity decline. Still more and more until the iron age of Kali spreads its shroud so dark and deadly. Like a bleak and dreadful winter, this Kali is the most dangerous age, when quarrel and hypocrisy befoul, when leaders are, but swindlers and fools, the age of darkness - kali has begun.