I had often wondered myself how long ago was, for instance, the Kasssapa sasana, the Konagamana sasana, and so on back into this mahakalpa and those even prior to this mahakalpa, in simple, direct millions or tens of millions or hundreds of millions or billions of years.
Then you get into the times of the Buddhas in other world-systems in this galaxy, then on to other galaxies, then yet on to other superclusters of galaxies. In truth, the numbers will be infinite – even of past Buddhas.
And all those Buddhas proclaimed the same Dhamma.
But all this is of no real value to the IMMEDIATE task of treading the Path – as Lal has pointed out. It is just an eagerness to satisfy curiosity, but that, if pursued to any lenght of time, will be at the expense of that immediate task.
For that reason, I have given up looking into these things. The one prevailing motive, the ‘ruling idea’ being that it is difficult to be born a human, and moreover being born a human in a Buddha sasana – and we are here, in a human bhava and in a Buddha sasana. It is a duty to oneself to make the most of it.
With Noble Ones it is a duty to others as well, as we can see for ourselves.