How science works
How do we know what the
structure of the Earth is like, if we
have never seen it?
Answers
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 more limited opportunities samples, so scientists also rely on analyses of seismic waves and gravity, as well as magnetic studies.
Where the crust has been disturbed, it is easy to see layers of different materials that have settled and compacted. Scientists recognize patterns in these rocks and sediment, and they can evaluate the composition of rocks and other samples taken from different depths of the Earth during routine excavation and geologic studies in the lab. The United States Geological Survey Core Research Center has spent the past 40 years amassing a rock core and cuttings repository and making these samples available for study. Rock cores, which are cylindrical sections brought to the surface, and cuttings (sand-like particles) are kept for potential re-analysis as improving technology allows for more in-depth study. In addition to visual and chemical analyses, scientists also try to simulate conditions deep under the Earth’s crust by heating and squeezing samples to see how they behave under those conditions. More information about the Earth's composition comes from studying meteorites, which provide information about the likely origin of our solar system.