Hmmm, I don’t think you remember the concept correctly, or else the source you saw was mixing up a poetic figure of speech with a formal quantitative definition.
The kalpa is formally defined in classical Indian cosmology as a period of 4,320,000,000 years. Yes, that period can be broken down into standard subunits such as mahayugas or manvantaras. But there’s nothing more intrinsically weird about its structure than about defining a century as 100 years or a millennium as 1000 years.
Why did we switch to plural at the end? Shouldn’t it be “millennium by millennium”? (Or, if we’re going the other way, “Hours by hours, days by days…”)
Which, as it turns out, is a surprisingly convenient unit, being approximately both the half-life of uranium-238 and the current age of the Solar System and everything in it.
Much older. The “kalpa=1000 mahayugas” and related chronometrology appears to be part of a late-BCE/early CE synthesis of cosmology and astronomy, with some influence from Hellenistic and Babylonian base-60 period relations models.
Wow…I wouldn’t think ancient peoples would be contemplating such big amounts of time. Heck, even today there are some religious nuts who think the earth is only ~6,000 years old. 4.3 billion years is way out of that ballpark.
Also, happy cake day! 26 years…one of the ancients!