I found that the "Reasoning" book actually gives a rather detailed explanation. I can tell Listener & Gumby were paying attention.
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rsp.113-p.114Earth***Will
Godhimselfdestroytheearthbyfire?Does 2 Peter 3:7, 10 (KJ) support that view? "The heavens and the earth, which are now, by the same word are kept in store, reserved unto fire against the day of judgment and perdition ["destruction," RS] of ungodly men. . . . The day of the Lord will come as a thief in the night; in the which the heavens shall pass away with a great noise, and the elements shall melt with fervent heat, the earth also and the works that are therein shall be burned up ["burned (burnt) up," RS, JB; "will vanish," TEV; "will be made manifest," NAB; "will be laid bare," NE; "will be discovered," NW]." (Note: The Codex Sinaiticus and Vatican MS 1209, both of the 4th century C.E., read "be discovered." Later manuscripts, the 5th-century Codex Alexandrinus and the 16th-century Clementine recension of the Vulgate, read "be burned up.")
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rsp.114par.4Earth***Note that, in the context, at 2 Peter 3:5, 6 (also 2:5, 9), a parallel is drawn with the Flood of Noah’s day, in which wicked human society was destroyed, but Noah and his household, as well as the globe itself, were preserved. Likewise, at 2 Peter 3:7 it says that the ones to be destroyed are "ungodly men." The view that "the earth" here refers to wicked human society fully agrees with the rest of the Bible, as is illustrated by the texts cited above. It is that symbolic "earth," or wicked human society, that is "discovered"; that is, Jehovah will sear away as by fire all disguise, exposing the wickedness of ungodly human society and showing it to be worthy of complete destruction. That wicked society of humans is also "the first earth," referred to at Revelation 21:1 (KJ).