Final answer:
Mountains can act as barriers to migration while rivers can make migration easier. Plains, forests, deserts, and oceans have varying levels of impact on migration. Valleys can act as barriers or facilitators depending on their characteristics.
Step-by-step explanation:
Mountains can act as barriers to migration because they are difficult to cross. For example, the Himalayas in Asia serve as a barrier between India and China, making migration difficult between the two countries.
On the other hand, rivers can make migration easier as they provide a natural transportation route. For instance, the Mississippi River in the United States has historically facilitated migration and trade.
Plains, forests, and deserts do not necessarily act as barriers to migration. They can be crossed relatively easily, although certain features within these landforms, such as dense forests or sand dunes in a desert, may pose challenges.
Oceans can also be seen as barriers to migration, as crossing them requires specialized means of transportation.
Valleys, like mountains, can also act as barriers to migration if they are difficult to cross due to steep slopes or other physical features. However, if the slopes are gradual and the valley provides a natural transportation corridor, it can make migration easier.
For example, the Great Rift Valley in Africa has served as a migration route for humans and animals for thousands of years.