What are the two ways we describe the layers of the Earth?

What is the mostly tropical region in asia

The creation of the trans-siberian railway allowed people to travel across russia. how could this railway impact russian culture?

How have ethnic groups shaped the population in central america and the caribbean? how has migration shaped the population in central america and the caribbean? how has small land areas shaped population in central america and the caribbean? how has a rapid population growth shaped the population in central america and the caribbean?