Normally, one updates information with newer ones. I however choose to let the pages about the history of the Bhagavad Gita, the appearance of Lord Rama and description of the 28th catur yuga remain online.
Why?
So that one can see that trying to understand the Supreme Personality of Godhead Krishna is very difficult. After thinking and investigating I have some updated information about above mentioned 3 pages. You can compare them.
Krishna can only be understood through love, not through work or intelligence. Take care. Hare Krishna!
1728000 years = duration of Satya Yuga
1296000 years = duration of Treta Yuga
864000 years = duration of Dvapara Yuga
432000 years = duration of Kali Yuga
4320000 years = catur yuga (satya+treta+dvapara+kali yugas)
71 catur yugas = 1 Manvantara (71x4320000) = 306720000 years. = Reign of one Manu (father of Mankind), son of Lord Brahma.
14 Manvantaras = (14x306720000) = 4294080000 years
15 Junctures after each Manvantara = (15x1728000) = 25920000 years
So 14 Manvantaras + 15 Junctures = 1 day of Brahma = 4320000000 years (1 kalpa)
We are now in Sveta-Varaha Kalpa, 7th Manvantara, 28th catur yuga, 5120 years in Kali yuga.
We have already passed through the previous 6 Manvantaras in Brahma's day: 6x306720000 = 1840320000 years
We have already passed through the previous 7 Junctures after each Manvantara: 7x1728000 = 12096000 years
We have already passed through 27 catur yugas in the 7th Manvantara: 27x4320000 = 116640000 years
We have already passed through Satya, Treta, Dvapara and part of Kali yuga in 28th catur yuga of the 7th Manvantara: 1728000 +1296000 +864000 +5120 (kali yuga now started 3102bce + 2018) = 3893120 years
Since start of Sveta-Varaha Kalpa 1972949120 years have passed.
Time remaining in current day of Brahma (1 Day of Brahma - Time passed in current day) = 4320000000 - 1972949120 = 2347050880 years.
Age of current Manu (Vaivasvata) aka Time passed in current Manvantara:
-27 catur yugas: 27x4320000 = 116640000 years
-Time passed in current Catur Yuga[1728000+1296000+864000+5120] = 3893120 years
Total = 116640000 + 3893120 = 120533120 years.
So start of 7th Manvantara, before birth of Vaivasvata Manu (120533120 years ago): the Gītā was spoken by the Lord to His disciple the sun-god Vivasvān, a rough estimate is that the Gītā was spoken at least 120,400,000 years ago.
Bhagavata Purana clearly states that Lord Rama became king during Treta yuga (Bhag. 9.10.51).
In the Vayu Purana (70.47-48) [published by Motilal Banarsidass] there is a description of the length of Ravana’s life. It explains that when Ravana’s merit of penance began to decline, he met Lord Rama, the son of Dasarath, in a battle wherein Ravana and his followers were killed in the 24th Treta-yuga. The Roman transliteration of the verse is:
tretayuge chaturvinshe ravanastapasah kshayat
ramam dasharathim prapya saganah kshayamiyavan
The same Ramayana that gives the planetary descriptions (on which the above calculation is based) also tells that Lord Rama came in Treta-yuga.
The Matsya Purana (47/240,243-246) is another source that also gives more detail of various avataras and says Bhagawan Rama appeared at the end of the 24th Treta-yuga.
Time elapsed in 7th Manvantara, 24th catur yuga, at the end of Satya yuga:
-23 catur yugas: 23x4320000 = 99360000 years
-Time elapsed at the end of Satya yuga = 1728000 years
Total = 101088000 years.
Difference between start Vaivasvata Manu till now (28th catur yuga) and start Vaivasvata Manu till 24th catur yuga = 120533120 - 101088000 = 19445120 years.
In https://prabhupadabooks.com/bg/4/1 it is said
The Blessed Lord said: I instructed this imperishable science of yoga to the sun-god, Vivasvān (120533120 years ago), and Vivasvān instructed it to Manu, the father of mankind, and Manu in turn instructed it to Ikṣvāku.
"In the beginning of the Tretā-yuga [millennium] this science of the relationship with the Supreme was delivered by Vivasvān to Manu (2165120 years ago). Manu, being the father of mankind, gave it to his son Mahārāja Ikṣvāku, the King of this earth planet and forefather of the Raghu dynasty in which Lord Rāmacandra appeared. Therefore, Bhagavad-gītā existed in the human society from the time of Mahārāja Ikṣvāku."
Age of current Manu (Vaivasvata) aka Time passed in current Manvantara:
-27 catur yugas: 27x4320000 = 116640000 years
-Time passed till end of Satya, beginning of treta: 1728000 years.
Total = 118368000 years.
Difference between start Vaivasvata Manu till now (28th catur yuga) and start Vaivasvata Manu till 28th catur yuga, end of Satya and beginning of Treta = 120533120 - 118368000 = 2165120 years
Accepting that before the birth of Manu the Gītā was spoken by the Lord to His disciple the sun-god Vivasvān, a rough estimate is that the Gītā was spoken at least 120,400,000 years ago; and in human society it has been extant for two million years. It was respoken by the Lord again to Arjuna about five thousand years ago.
BG 4.1, Translation and Purport: The Personality of Godhead, Lord Śrī Kṛṣṇa, said: I instructed this imperishable science of yoga to the sun-god, Vivasvān, and Vivasvān instructed it to Manu, the father of mankind, and Manu in turn instructed it to Ikṣvāku.
In the Mahābhārata (Śānti-parva 348.51-52) we can trace out the history of the Gītā as follows:
tretā-yugādau ca tato
vivasvān manave dadau
manuś ca loka-bhṛty-arthaṁ
sutāyekṣvākave dadau
ikṣvākuṇā ca kathito
vyāpya lokān avasthitaḥ
"In the beginning of the millennium known as Tretā-yuga this science of the relationship with the Supreme was delivered by Vivasvān to Manu. Manu, being the father of mankind, gave it to his son Mahārāja Ikṣvāku, the king of this earth planet and forefather of the Raghu dynasty, in which Lord Rāmacandra appeared. Therefore, Bhagavad-gītā existed in human society from the time of Mahārāja Ikṣvāku."
The cycle of Satya is characterized by virtue, wisdom and religion, there being practically no ignorance and vice, and the yuga lasts 1,728,000 years. In the Tretā-yugavice is introduced, and this yuga lasts 1,296,000 years. In the Dvāpara-yuga there is an even greater decline in virtue and religion, vice increasing, and this yuga lasts 864,000 years. And finally in Kali-yuga (the yuga we have now been experiencing over the past 5,000 years) there is an abundance of strife, ignorance, irreligion and vice, true virtue being practically nonexistent, and this yuga lasts 432,000 years. So one Catur Yuga = 4320000 years
One day of Brahma contains 14 Manvantaras (including 15 junctures)
1 Day of Brahma has 14 Manu's, and each Manvantara (1 life span of Manu) lasts 71 years of these Catur Yugas, or Dvipa yuga or Maha yugas (71x4320000) = 306720000 years.
1 Manvantara Juncture (Sandhya - Interval between Manvantaras) = 1728000 years
1 Daytime of Brahma (14 Manvantaras[14x306720000]+15 Junctures[15x1728000]) = 4294080000 + 25920000 = 4320000000 years. (1 kalpa, day or night duration)
1 Manvantara = 306720000 years.
Before Vaivasvata Manu's reign started, The reign of 6 Manu's was already completed: 1840320000 years. (1 billion 840 million 320 thousand years) --> 6 x 306720000 years
We are now in the reign of the 7th Manu (Vaivasvata). In this reign, 27 Catur Yugas have already passed: 116640000 years. (116 million 640 thousand years) --> Accepting that before the birth of Manu the Gītā was spoken by the Lord to His disciple the sun-god Vivasvān, a rough estimate is that the Gītā was spoken at least 120,400,000 years ago;
In the 28th Catur Yuga, 1 Satya yuga, 1 Treta yuga and 1 Dvapara yuga and 5120 years in Kali Yuga (now) has already passed: 3893120 years. (3 million 893 thousand 120 years) --> and in human society it has been extant for two million years. 3893120 - 5120 - 864000 - 1296000 = 1728000
In beginning of Treta Yuga, Vivasvan gave the science of Bhagavad Gita to his son Vaivasvata Manu
Vaivasvata Manu gave the science of Bhagavad Gita to King Iksvaku during the Treta Yuga. So: 3893120 - 5120 - 864000 - 1296000 = 1728000 years ago. (roughly 2 million years ago).
Sri Krishna respoke Bhagavad Gita again to Arjuna about five thousand years ago (3067 BCE), at the end of Dvapara Yuga in 28th Catur Yuga.