The Earth’s Structure. series of layers or spheres which differ in density, chemistry (or composition) and physical properties. Density. is the relative heaviness of a substance defined as the mass per unit volume usually expressed in g/cm 3 EARTH HAS DENSITY STRATIFICATION.
What evidence supports the idea that Earth has layers?
The behavior of seismic waves generated by earthquakes give scientists some of the best evidence about the structure of Earth.
(a) If Earth were uniform (homogeneous) throughout, seismic waves would radiate from the site of an earthquake in straight lines.
(b) If the density, or rigidity, of Earth increased evenly with depth, seismic wave velocity would increase with depth, and the waves would bend smoothly upward toward the surface.
(c) If Earth were layered inside, some seismic waves would be reflected at the boundaries between layers while others were bent. Seismic evidence shows that Earth is layered.
Fig. 3-11, p. 57 Asthenosphere Plastic?