What is geologic time, and how does it work?

We all recognise the names of some time periods such as Jurassic or Devonian - but how many us of actually understand how geologists divide up the earth's past?

I'm sure you all remember where you were when you found out that the statistical correlation of magneto-biostratigraphic calcareous nannofossils with M-sequence magnetic anomalies approximated new boundaries for Tethyan Kimmeridgian of Sardinia (Muttoni et al. 2018). I was on my laptop at the time.

I'll confess, I struggle to even begin to understand what this new paper is about, beyond the broad principle that a chunk of the rock record as it relates to geological time is being slightly tweaked.