Question

What is the duration (Timeline) of the four “Yugas”?

Answer

I would agree with those answers, which suggest following durations:

  1. Krita Yuga 4800 years
  2. Treta Yuga 3600 years
  3. Dwapara Yuga 2400 years
  4. Kali Yuga 1200 years

Here is the scriptural proof from Moksha Dharma Parva (assuming that it's not interpolated):

I shall, in their order, tell thee the number of years, that are (thus) for different purposes computed differently in respect of the Krita, the Treta, the Dwapara, and the Kali yugas. Four thousand years (of the deities) is the duration of the first or Krita age. The morning of that epoch consists of four hundred years and its evening is of four hundred years. As regards the other yugas, the duration of each gradually decreases by a quarter in respect of both the substantive period with the conjoining portion and the conjoining portion itself.

Krita yuga is 4000 + 400 + 400 = 4800 years. Other subsequent Yuga-s reduce by quarter, i.e. 1200 (1000 + 100 + 100) years. I have found some issues with Sanskrit translation, but have accepted above.

There are some interesting counter questions to be discussed in this regard.

Q-1: "Are these human years or some divine years?"

चत्वार्याहुः सहस्राणि वर्षाणां तत्कृतं युगम्।
तस्य तावच्छती संध्या संध्यांशश्च तथाविधः ।।२०।।
Four thousand celestial years is the duration of the first or Krita age. The morning of that cycle consists of four hundred years and its evening is of four hundred years.

They are indeed human years. The above verse (Verse-20 from MahAbhArata book > Volume-8 > Chapter-231 > Page-178), does not show anything related to deity or celestial, even though it's translated such by few people.
Moreover, if we start multiplying according to "deity" years, then it will come up with very unrealistic figures, which are simply unbelievable.

Q-2: "Then what's the relation between human year & deity year?"

In the same source, we can find relation of human years with pitri-s & divine-s:

The sun makes the day and the night for the world of man. The night is for the sleep of all living creatures, and the day is for the doing of action. A month of human beings is equal to a day and night of the Pitris. That division (as regards the Pitris) consists in this: the lighted fortnight (of men) is their day which is for the doing of acts; and the dark fortnight is their night for sleep. A year (of human beings) is equal to a day and night of the gods. The division (as regards the gods) consists in this: the half year for which the sun travels from the vernal to the autumnal equinox is the day of the deities, and the half year for which the sun travels from the latter to the former is their night.

This is the only relation I could find between humans & deities/gods.

Q-3 "How the Brahman's time is related to humans?

From the same source, 12000 years make a Yuga ( = Krita + Treta + DwApara + Kali). Thousand such Yuga-s duration make Brahman's day (i.e. morning, to be specific) and Thousand such Yuga-s duration makes Brahman's night.

The learned say that these twelve thousand years constitute what is called a yuga. A thousand such yugas compose a single day of Brahman. The same is the duration of Brahman's night.

That means Brahman's full cycle constitutes 24 million years.

Q-4: "What happens during Brahma's day & night?

The manifestation occurs only during the 1st half of 12 million years. Remaining part is completely void or Moskha.

With the commencement of Brahman's day the universe begins to start into life. During the period of universal dissolution the Creator sleeps, having recourse to yoga-meditation. When the period of slumber expires, He awakes. That then which is Brahman's day extends for a thousand such yugas. His nights also extends for a thousand similar yugas. They who know this are said to know the day and the night. On the expiry of His night, Brahman, waking up, modifies the indestructible chit by causing it to be overlaid with Avidya. He then causes Consciousness to spring up, whence proceeds Mind which is identical with the Manifest.

This has a striking similarity with what Krishna said in Gita:

BG 8.17, 8.18, 8.19 - Knowing that thousand eras constitute a day of Brahman, [and] thousand eras complete a night, are the people who know day, [and] night. On arrival of day, all manifestations originate from "Unmanifest"; On arrival of night they annihilate into [what is] known as "Unmanifest" only. This [same] elementary world only happens again & again; Annihilates upon arrival of night, [and] originates upon arrival of day.

Q-5: "If manifestation happens within 12 million years, then what about dinosaurs?"

Dinosaurs happened supposedly before 65 million years before. Even so called "big bang" happened 4.5 billion years ago. And it's difficult to fit them in the 12 million box. This could be the inspiration for those, who come up with superlative figures of each yuga (e.g. 432000 years for Kali).

However, this can be explained in following ways:

  • Dinosaurs & Big bang were dated X million/billion years ago using certain technique. As certain principles change over time, this may also change. May be we don't have full knowledge of dating back.
  • Assume that the dating is 100% accurate. In such case, we may think of video game analogy. Super Mario is the most famous game in the world. It has multiple stages (i.e. 30+ depending on version). Each stage has its own imagination for animals & plants. However, Mario can be limited within this 30+ stages. If someone digs into the evolution of those animals & plants, then they may really find the duration beyond those 30+ rounds. But in reality, they never evolved like that. Mario, plants, animals, queen & dragon just existed.

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