The thick layer is the-crust
Radio waves are electromagnetic waves and as such travel at the speed of light. Waves emitted a century ago would be 100 hundred light years away. A light year is the distance light travels in one year. In one year light travels about 5.9 trillion miles. therefore the waves traveled about 590 trillion miles in a century.
Population is what they both have
Sustainable use practices are practices that are used in the use of resources for example that seek to maintain the longevity and continuance of the potential use of that resource. In regards to trees and logging the sustainable use of wood or paper would seek to continue the longevity and vitality of the forests by not overusing these products. Sustainable use will use a resource at a rate that will allow for natural replenishment or incremental use of the resource to prevent harm to the environment and allow the resource to be used far into the future.
