I. THE GREAT TRIBULATION: For then shall be great tribulation, such as was not since the beginning of the world to this time, no, nor ever shall be. And except those days should be shortened, there should no flesh be saved: but for the elect's sake those days shall be shortened. (Mt 24:21,22).
2. THE *SHAKING* OF THE HEAVENS AND THE EARTH: Immediately after the tribulation of those days shall the sun be darkened, and the moon shall not give her light, and the stars shall fall from heaven, and the powers of the heavens shall be shaken: (Mt 24:29)
THE SECOND COMING OF CHRIST
Now notice that it says "AND THEN" TWICE in the next verse after these things have occurred: And then shall appear the sign of the Son of man in heaven: and then shall all the tribes of the earth mourn, and they shall see the Son of man coming in the clouds of heaven with power and great glory. (Mt 24:30)
Everything you just quoted is from Matthew 24 and before verse 34 when Jesus says ALL these things will happen to this generation. His contemporaries.
Also notice that all the inhabitants of the earth will literally see Christ coming in power and great glory from Heaven, and they will weep and mourn because their judgment is coming.
The Greek word for earth is "Ges". It can be equally translated as land. In this case the land of Israel. They were weeping because they saw Jesus coming in judgment to destroy them for rejecting Him.