sentences:  The period from 2500 BC to 2000 BC has been called the "Late Neolithic/Early Bronze Age", in recognition of the difficulty of exactly defining this boundary.Some archaeologists recognise a British Chalcolithic when copper was used between the 25th and 22nd centuries BC, but others do not because production and use was on a small scale.In Ireland the final Dowris phase of the Late Bronze Age appears to decline in about 600 BC, but iron metallurgy does not appear until about 550 BC.