Which strategy can scientist use to learn about earths deepest layers

explanation:

since the crust is readily accessible, scientists have been able to perform hands-on experiments to determine its composition; studies on the more distant mantle and core have limited opportunities samples. so scientists also rely on analyses of seismic waves and gravity and as well as magnetic studies.

the first phase of the government’s plan for settlement was building the transcontinental railroad. the railroad provided a way to bring settlers and manufactured goods west and ship their agricultural and mining produce east. the transcontinental railroad was an essential artery for rapid development of the frontier.

the second phase of the government’s plan was a liberal land distribution policy that made it possible for many people to homestead. with these two key elements—transportation and cheap land—the government rapidly achieved its goal of persuading people to move west, settle on farms, and push back the frontier.