What does the inside of the Earth look like and why? Objective Students will be able to list and identify the different layers that make up the Earth and how gravity plays a role in the formation of the planet. Background Our planet Earth is composed of several layers. Each layer has a unique density (density = mass/volume). Scientists believe that all planets formed on the basis of gravity. Therefore, the layering of Earth is a result of gravitational pull. The densest layer (inner core) is at the center and the least dense layer (crust) is the outermost layer. The atmosphere, composed of gas Duration: 30 Minutes.