Structure of the Earth the crust, upper mantle, lower mantle, outer core, and inner core. The geologic component layers of Earth are at the following depths below the surface: The layering of Earth has been inferred indirectly using the time of travel of refracted and reflected seismic waves created by earthquakes. The core does not allow shear waves to pass through it, while the speed of travel (seismic velocity) is different in other layers. The changes in seismic velocity between different layers causes refraction owing to Snell's law, like light bending as it passes through a prism. Likewise, reflections are caused by a large
What Shall We Do Now? with D minor and A minor chords. Where the album's main character, Pink's question about how he should fill out the gaps in his wall was of a rhetorical nature in "Empty Spaces", "What Shall We Do Now?" lists the diversions, possessions, and vices of a rock star (""Shall we buy a new guitar / Shall we drive a more powerful car / Shall we work straight through the night / Shall we get into fights / Leave the lights on / Drop bombs ..."") in response. The two tracks are easily confused. The tape speed for "Empty Spaces" was