Structure of the Earth obducted onto the continental crust and preserved as ophiolite sequences. Many rocks now making up Earth's crust formed less than 100 million (1) years ago; however, the oldest known mineral grains are about 4.4 billion (4.4) years old, indicating that Earth has had a solid crust for at least 4.4 billion years. Earth's mantle extends to a depth of 2,890 km, making it the thickest layer of Earth. The mantle is divided into upper and lower mantle. The upper and lower mantle are separated by the transition zone. The lowest part of the mantle next to the core-mantle boundary is
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