There is no reason, for example, why the north Europeans should stop using bronze and start using iron abruptly at the lower boundary of the Subatlantic at 600 BC. In the warm Atlantic period, Denmark was occupied by Mesolithic cultures, rather than Neolithic, notwithstanding the climatic evidence. Moreover, the technology stages vary widely globally. The Pleistocene phases and approximate calibrated dates (see above) are:  The Holocene phases are:  Some marker plant genera or species studied in peat are  More sphagnum appears in wet periods. Dry periods feature more tree stumps, of birch and pine.