SuttaCentral
I really like and agree with your concluding paragraph @DKervick…
Of course I think that kamma is real and important - at the very least, it seems worth taking seriously. But there are differences of opinion about these things: a fact that has to be accepted.
Be well
According to the simile given in Sāsapasutta kappa can be approximated.
Suppose there was an iron city, a league long, a league wide, and a league high, full of mustard seeds pressed into balls.
“Seyyathāpi, bhikkhu, āyasaṃ nagaraṃ yojanaṃ āyāmena yojanaṃ vitthārena yojanaṃ ubbedhena, puṇṇaṃ sāsapānaṃ guḷikābaddhaṃ.
And as each century passed someone would remove a single mustard seed.
Tato puriso vassasatassa vassasatassa accayena ekamekaṃ sāsapaṃ uddhareyya.
By this means the huge heap of mustard seeds would be used up before the eon comes to an end.
Khippataraṃ kho so, bhikkhu, mahāsāsaparāsi iminā upakkamena parikkhayaṃ pariyādānaṃ gaccheyya, na tveva kappo.
Assuming the span of a kappa can be can be calculated using above simile;
The equivalent length of a yojana as about 13 km (8 mi) throughout his translations of the Bhagavata Purana.
And “Karma vipāka” a book by Nauyane Ariyadhamma Thero says it is 16 mi.
Assuming it is 8 mi, the calculation.
However, according to Pabbatasutta the calculated value must be far greater than this value since a fine cloth from Kāsī would not be able to remove same amount to a mustard seed from the rock. Therefore, calculating a value using the simile is not that accurate.
This just is to have an approximation. 
1 eon > 2.13410909 × 10^23 years (~213 sextillion)
Ajahn Brahmali’s calculation shows it is 36.8 billion years. 213 sextillion >>> 36.8 billion
I think this information can help…
The Wheel-turning Emperor (Excerpt)
Cakkavatti Sutta (DN 26)The body of this sutta consists of a narrative illustrating the power of skillful action. The narrative states that, in the past, unskillful behavior was unknown among the human race. As a result, people lived for an immensely long time—80,000 years—endowed with great beauty, wealth, pleasure, and strength. Over the course of time, though, they began behaving in various unskillful ways. This caused the human life span gradually to shorten, to the point where it now stands at 100 years, with human beauty, wealth, pleasure, and strength decreasing proportionately. In the future, as morality continues to degenerate, human life will continue to shorten to the point were the normal life span is ten years, with people reaching sexual maturity at five. “Among those human beings, the ten courses of action (see AN 10:176) will have entirely disappeared.… The word ‘skillful‘ will not exist, so from where will there be anyone who does what is skillful? Those who lack the honorable qualities of motherhood, fatherhood, contemplative-hood, & brahman-hood will be the ones who receive homage.… Fierce hatred will arise, fierce malevolence, fierce rage, & murderous thoughts: mother for child, child for mother, father for child, child for father, brother for sister, sister for brother.”
Ultimately, conditions will deteriorate to the point of a “sword-interval,” in which swords appear in the hands of all human beings, and they hunt one another like game. A few people, however, will take shelter in the wilderness to escape the carnage, and when the slaughter is over, they will come out of hiding and resolve to take up a life of skillful and virtuous action again. With the recovery of virtue, the human life span will gradually increase again until it reaches 80,000 years, with people attaining sexual maturity at 500. Only three diseases will be known at that time: desire, lack of food, and old age. Another Buddha—Metteyya (Maitreya)—will gain awakening, his monastic Saṅgha numbering in the thousands. The greatest king of the time, Saṅkha, will go forth into homelessness and attain arahantship under Metteyya’s guidance.
The story, after chronicling the ups and downs of human wealth, life span, etc., concludes with the following lesson on kamma and skillful action.
DN 26 Cakkavatti Sutta | The Wheel-turning Emperor (Excerpt)
Chatur Yugas, the four epochs of time
The Puranas divide each cycle of creation into four divisions or epochs, called Yugas. Together, they constitute one Mahayuga (great epoch). Each Yuga has a specific time frame, a definite purpose and certain characteristic features which distinguish it from the others. Their sequence is fixed. The time frame of each Yuga varies. The four epochs are stated below.
- Satya-yuga or Satyuga, the Yuga of Truth, also called Krita-yuga, which lasted for 1,728,000 earth years
- Treta-yuga, the second Yuga, which lasted for 1,296,000 earth years
- Dwapara-yuga, the third Yuga which lasted for 864,000 earth years
- Kali-yuga, the fourth Yuga or the age of darkness, which lasted for 432,000 earth years
Thus, each Mahayuga, comprising the four Yugas, has the duration of 4,320,000 earth years. According to our scriptures the world has already passed through the first three Yugas, and currently it is passing through the fourth one namely the Kali Yuga. At the end of it, the world will come to an end in a great conflagration.
Learn about the mass extinction event 66 million years ago and the evidence for what ended the age of the dinosaurs.
Dinosaur extinction facts and information | National Geographic
Is the yuga a measure of human civilisation?
Even 4 Mahayuga is merely 18 million years. Too small compared to age of Earth (4.5 billion), or age of universe (13.8 billion) but too large for current knowledge of human evolution (1-2 million years).
Anyway, I highly doubt such numbers. Ancient India was not famous for accuracy in large numbers maths.
They are Cycles …
Buddhist cosmology of the Theravada school
Human Beings (manussa loka)
Manu (Hinduism)
Manu (Sanskrit: मनु) is a term found with various meanings in Hinduism. In early texts, it refers to the archetypal man, or to the first man (progenitor of humanity). The Sanskrit term for ‘human’, मानव (IAST: mānava) means ‘of Manu’ or ‘children of Manu’.[1] In later texts, Manu is the title or name of fourteen mystical Kshatriya rulers of earth, or alternatively as the head of mythical dynasties that begin with each cyclic kalpa (aeon) when the universe is born anew.[1] The title of the text Manusmriti uses this term as a prefix, but refers to the first Manu – Svayambhuva, the spiritual son of Brahma.[2]
In the earliest mention of Manu, in the Rigveda, Manu is only the claimed ancestor of the “Five Peoples”, or “Páñca Jánāḥ” (the five tribes being the Anus, Druhyus, Yadus, Turvashas, and Purus). The Indo-Aryans considered all other peoples to be a-manuṣa.[3]
According to Puranas, each kalpa consists of fourteen Manvantaras, and each Manvantara is headed by a different Manu.[1] The current universe, is asserted to be ruled by the 7th Manu named Vaivasvata.[2]
In Vishnu Purana, Vaivasvata, also known as Sraddhadeva or Satyavrata, was the king of Dravida before the great flood.[4] He was warned of the flood by the Matsya (fish) avatar of Vishnu, and built a boat that carried the Vedas, Manu’s family and the seven sages to safety, helped by Matsya. The tale is repeated with variations in other texts, including the Mahabharata and a few other Puranas. It is similar to other flood such as that of Gilgamesh and Noah.[5]
Manu (Hinduism) - Wikipedia
Manvantara
A manvantara, in Hindu cosmology, is a cyclic period of time identifying the duration, reign or age of a Manu, the progenitor of mankind. In each manvantara, seven Rishis, certain deities, an Indra, a Manu, and kings (sons of Manu) are created and perish.[1] Each manvantara is distinguished by the Manu who rules/reigns over it, of which we are currently in the seventh manvantara of fourteen, which is ruled by Vaivasvata Manu.[2][3]
Each manvantara lasts for 306,720,000 years and repeats seventy-one Yuga Cycles (dharmic ages). There are a total of fourteen manvantaras in a kalpa (day of Brahma), where each manvantara is followed by and the first preceded by a manvantara-sandhya (fifteen connecting periods), where each sandhya lasts for 1,728,000 years (the duration of a Satya Yuga). During each manvantara-sandhya, the earth (Bhu-loka) is submerged in water.[4][5][6]
Manvantara - Wikipedia
Lists of Buddhas
The Seven Buddhas of Antiquity
The 29 Buddhas of Theravāda
Oh, I have not (much) issue with Buddhist cosmology and cyclic multiverse models. See the link for what I wrote for physics and Buddhism.
It’s just that I don’t think Hindu sources are reliable, especially their explicit numberings as compared to Buddha’s usage of analogy without numbers.
Say, kalpa.
So, age of universe is 13.8 billion years, we don’t expect the universe to end so soon, even in Big Rip scenario, we have still 22 billion years from now. From this, we expect a kalpa to be at least more than this number. But from your quotes:
A kalpa is less than 4.5 billion years. Thus casting doubt about the whole issue. If we remove the numbers and just have some rough numbers, it’s a bit better.
The thing that bothers me the most about the accounts of the distant past and future in the suttas is that they are simply echos of the times they were written in. So in the distant past and future we have the caste system and a monarchy, just like in ancient India. Personally, I loathe to think that the caste system is some universal constant. In fact, I’d go so far as to say it’s one of the worst things that Indian thought and culture has contributed to the world. Anyway, I think it was just a lack of imagination on the authors’ part. They couldn’t imagine the world ever being any different. If they had come up with societies and systems of governance that were radically different from India, I’d be more inclined to believe them. Frankly, the Mahayana writers showed a lot more imagination when they came up with alternate dimensions, etc., like the Pure Lands, than the authors of the more fanciful parts of the EBTs did.
Racism can be seen as a form of caste system. We are born into a race, cannot change it. Racism seems quite widespread, including the anti-chinese racism associated with covid 19.
Although theoretically class system allows for social mobility, practically speaking, many people who are born poor tend to have less opportunity to climb the ladder. It maybe a convenient mass delusion to keep the masses at hard work. It’s also so easy to fall off the ladder, as compared to getting up. One mistake as a doctor giving the wrong medicine, loss the license to heal. So class system is a form of caste system actually too. Sons of billionaires tend to inherit the wealth, and live without working on the interests on the money in their bank, while the rest of the masses toil like ancient slaves.
Even nationality is a form of caste system. People of some nationality (like USA, Singapore), can travel almost anywhere easily, whereas people of other nationalities have a harder time to get all the visas etc. Malaysians tend to see Indonesians (Bangladesh) as maids source (manual, hard labour). Singaporeans tend to see Malaysians as taking away their jobs, and a cheaper land to get petrol. While westerners tend to get treated better in Malaysia and Singapore, a remnant of the colonisation period where the west marketed themselves as more enlightened and technologically superior.
Just use creative mapping, it’s easy to map caste system to any society which is not egalitarian.
It’s not easy to imagine future possible forms of sociology and political structures, even as science fiction writers. It’s possible that they see these from past life recollection, and only have the limited vocab of those days to present it to their audiences. Short of actually producing new terms, with books to define, what’s a planetary hegemony, or president of a country with constitutional democracy, etc.
Yes, there’s already enough racism, sexism, classism, ageism, etc., in the world. We don’t need to add the idea of caste to the mix.
yes these numbers are a little complex
Add to that speciesism. For humans to think it’s ok to eat animals.
News…
Humanlike Footprints in Crete Dated to 6 Million Years Muddle Archaeologists
Somebody was strolling on a beach in Crete 6 million years ago: Earliest ancestor of humans or just another ape?
Tracing human origins by foot
Six-million-year-old Cretan footprints challenge beliefs about human evolution**
Are There Lost Alien Civilizations in Our Past? - YouTube
How easily civilizations even on agriculture technology disappears in time.
I am not an expert on past Buddhas, but it may be of interest that a number of traditions around the robes of previous Buddhas describe them as having antelope skin robes, for example, in Gandhari and Chinese sources (memory is vague on the latter, maybe in something by Daoxuan).