Geological time is broken up into eons, eras, periods, epochs etc. generally based on significant changes to the status quo.
These changes are usually radical alterations to climate or other conditions that often have resulted in mass extinctions, or other major upheavals. These are generally global in impact and can be identified quite easily where they occur, documented in rock strata in suitable locations worldwide.
We live in one such subdivision of the Pleistocene epoch, the Holocene... that starts at the end of the Ice age that preceded it.
The Holocene is markedly different from the other epochs that precede it in that temperatures and sea levels have been remarkably stable (by geological standards) more especially so, for the last 5000 years. It is intriguing to note that it is specifically this stability that has allowed the emergence of agriculture and civilization as we know it.
A reasonably stable sea level resulted in the deposition of very large fertile deltas and other stable alluvial deposits. It is on these fertile patches that homo sapiens has been able to settle and develop agricultural practices.
This change from hunter gatherer and nomadic lifestyles to more fixed and increasingly populated environs is what led to the emergence of more stratified societies and the complex interactions we call civilization.
With civilization, mass food production and suitable technological advancement the human population has exploded.
It's intriguing and at the same time disconcerting to note that a large percentage of the human population still resides in these cradles of civilization and other low lying coastal areas.
The reason that this is disconcerting is that the "just right" or Goldilocks conditions that have brought about these relatively stable temperatures and sea levels are a geological rarity.
Even aside from or tinkering with the levels of greenhouse gasses in our atmosphere, from a geological perspective we are somewhat overdue for a climate swing and radical change in temperatures and sea levels.
It is precisely this stability that enabled modern society to emerge but it may be our over-reliance on and the breach of this stability that will bring about our demise on a large scale and usher in the next geological epoch.
Already there is movement afoot to recognize a new epoch "the Anthropocene" recognizing the radical effect the human species has had on the planet in the last couple of centuries.