To put artifacts in their proper context I consider it most important to pay attention to the chronological sequence, and I believe that the old idea of first stone, then copper, and finally iron, appears to be ever more firmly established as far as Scandinavia is concerned. ~ C.J. Thomsen
In 1816, while organizing antiquities for the then-new Danish National Museum in Copenhagen, C.J. Thomsen decided to present the goods chronologically.
Previous scholars had proposed that prehistorical implements had advanced from an age of stone tools to those of bronze and iron. Thomsen turned this treatment into a chronology applied to artifacts. Hence prehistory got divided into a 3-age system.
The Stone Age
The Bronze Age
The Iron Age
The 3-age system is widely known and wildly outmoded for its oversimplification in lacking worldwide application. For example, a bronze phase is not found everywhere. The transition from one age to the next is both uncertain and non-uniform geographically.
Writing became common during the Bronze Age: hence the history of prehistory overstays its welcome.
Most telling is that the 3 ages tell nothing of the way of life; instead, merely suggesting the state of materials technology. For all that, the 3-age system is so well-known that its use continues, as does its subdivisions.
The standard archeological habit seems to be tripartite divisions, with the usual names of Early, Middle, and Late, but Stone Age divisions are termed Old, Middle, and New. At some unrecorded date, the Stone Age was updated with swankier stone-based divisions now favored by archeologists: Paleolithic (palaios being Greek for old), Mesolithic (mesos = Greek for middle) and Neolithic (neos = Greek for new); lithos being Greek for stone.
Borrowing from geology, each of the Paleolithic age divisions have their own tripartite splits: Lower, Middle, and Upper, referring to age by physical strata (the lowest being the oldest).