Reconstructed setting· The columns of time

Mammoth steppe

45 ka → 11.7 ka

This backdrop shows the mammoth steppe, a cold, dry, treeless grassland that covered much of the northern hemisphere until the end of the last ice age.

Backdrop representing a vanished biome: a cold, dry, treeless formation dominated by herbaceous plants and grazed by mammoth, horse and steppe bison. It covered much of the northern hemisphere until the end of the last glaciation.

What the evidence shows

Fifty thousand years of ancient DNA extracted from sediments establish the plant composition of this environment, which contradicted expectations. It was not a grass tundra but a dry steppe dominated by flowering plants that are neither grasses nor shrubs, designated by the term forbs. The same sedimentary DNA identifies among the herbivores mammoth, horse and steppe bison. The absence of shrubs from the composition is deliberate: it is precisely the expansion of birch and willow thickets that marks the collapse of the biome, 13,900 to 13,200 years ago.

Bounds and conventions

No present-day landscape constitutes a satisfactory analogue, which makes this the most difficult backdrop on the timeline to establish. The plant record on which it rests is circumpolar, but the dating of the collapse comes from pollen and sedimentary DNA of eastern Beringia, where the shift was not uniform, the steppe persisting where slope and exposure kept the soil dry. The same biome extended as far as western Europe, where its aspect may have differed.