Which environmental change allowed people to travel by land between Asia and North America?
A. human adaptation to Arctic environments
B. the introduction of horses to North America
C. the formation of ice sheets on land
D. a rise in ocean temperatures
C. The formation of ice sheets on land.
During the last Ice Age, which peaked around 20,000 years ago, thick ice sheets covered much of North America and Asia. This lowered sea levels, exposing a land bridge called Beringia, which connected the two continents. This allowed early humans to travel from Asia to North America by foot. As the ice sheets began to melt around 10,000 years ago, the land bridge disappeared, leaving the continents separated again.