Abstract <p>Assigning the first Russian and the world’s longest 377-year “charcoal” tree-ring chronology (TRC) to the calendar time scale, multiple radiocarbon dating of charcoal fragments from archaeometallurgical slags and the find of tree bark have shown that the box-shaped iron-smelting furnaces of the Kosh-Agach type in the Chuya–Kurai paleo-metallurgical province (Russian Altai) functioned in the 7th–8th centuries AD, i.e., in Old Turkic times. These results clarify the recently announced problem of “ancient Turkic metallurgy paradox,” the inexplicable sudden disappearance of iron production in Southern Siberia in the 7th century AD. The constructed “charcoal” TRC indicates that the “old wood” effect in the high mountainous Chuya-Kurai region is at least 290–370 years, and the enrichment of slags with ancient parts of wood of long-lived trees does not allow the direct estimation of smelting time even with numerous ¹⁴C dating. The only way to solve the “old wood” problem is to date the bark, which is a unique find. Cross-dating of charcoal fragments from the three distant paleo-metallurgical sites shows the presence of a common climatic signal: as early as about 1.5–1.3 kyr ago, the currently forestless eastern periphery of the Chuya basin was occupied by tree vegetation, which completely vanished under conditions of progressive aridization and massive cutting down by nomads for economic needs.</p>