Yugas ... the four yugas are Satya, Treta, Dvapara, and Kali.

 The four yugas

Satya Yuga

Also known as the Golden Age, this is the first and most virtuous yuga. It's characterized by high spirituality, morality, and righteousness. 

Treta Yuga

Also known as the Silver Age, this yuga is marked by a decline in spirituality. People learn to use their intuition and are peace-loving and compassionate. 

Dwapara Yuga

Also known as the Bronze Age, this yuga is characterized by the emergence of suffering. People are self-interested and motivated by selfish goals. 

Kali Yuga

Also known as the Iron Age, this is the present age. It's characterized by ignorance and materialism. 

Kali Yuga, which lasts for 432,000 years, is believed to have started in 3102 BCE. Near the end of Kali Yuga, when virtues are at their worst, a cataclysm and a re-establishment of dharma occur to usher in the next cycle's Krita (Satya) Yuga, prophesied to occur by Kalki.

The Cycle of Four Yugas

The precession (caused by gradual rotation of the Earth’s axis) of the equinoxes is the period of time that it takes the Earth’s axis to pass through one complete cycle of the zodiac. It takes the planet 72 years to pass through one degree of the zodiac and 25,920 years to complete one full circle of 360 degrees. One half of the journey takes 12,960 years and covers the four yugas. Satya Yuga lasts 5184 years. Treta Yuga lasts 3888 years. Dwapara Yuga lasts 2592 years. Kali Yuga lasts 1296 years. These four yugas taken together come to a total of 12,960 years

When did Kali Yuga start?

The story of Mahabharat needs to be seen in a certain context. In 3140 BCE, the Kurukshetra War ended, and in 3102 BCE, Krishna left his body. Three to four months after the war, the Kali Yuga began. As of 2012 AD, Krishna’s era ended 5,114 years ago. If you subtract 2592, which is the cumulative number of years of the two Kali Yugas that are at the bottom of the ellipse which describes the axial precession, you arrive at 2522 years. That means we have already completed 2522 years of Dwapara Yuga, and since its total duration is 2592 years, we still have 70 years until its completion. In the year 2082, we will complete Dwapara Yuga and move on to Treta Yuga. The world will go through another upheaval, not necessarily in terms of war but probably in terms of population explosion and natural calamities, before moving on to this new era of wellbeing and upward movement of human consciousness.