The warming of Earth’s atmosphere continued until about 4000 b.c.e., with wide ranging global effects. Sea levels rose, flooding coastal areas, while glacial run-off filled interior waterways. The glaciers receded northward, along with the arctic and subarctic environments that had formerly extended into what are now the lower forty-eight states of the United States. Treeless plains and evergreen forests gave way to deciduous forests in the East, grassland prairies on the Plains, and desert in much of the West. The regional environments we know today emerged during this period.
