What happens to the earth at the return of Christ?
At the return of Christ, the heavens are shaken, the sun and moon are darkened, and the earth is left emptied, wasted, and desolate, with only a few people surviving out of the multitudes who once lived.
When Christ appears in the clouds, tremendous disturbances shake the whole created order. The sun is darkened, the moon no longer gives her light, and the stars fall from heaven; the powers of the heavens are shaken. Immediately after this, the sign of the Son of man appears, and every tribe on earth mourns because they see Him coming in power and great glory. The Jews especially, recognizing Him as the One they pierced, weep bitterly, as one mourns for a firstborn son.
At this same time the heaven departs like a scroll rolled together, every mountain and island is moved out of its place, and the earth and heavens shake. Kings, great men, rich men, captains, the mighty, and every bondman and free man try to hide themselves in dens and among the rocks, crying out for the mountains to fall on them and hide them from the wrath of the Lamb, because the great day of His wrath has come and none can stand.
The earth itself is described as being made empty, wasted, and turned upside down, with its inhabitants scattered. Every class of society, priest and people, master and servant, buyer and seller, lender and borrower, faces the same judgment, for station in life makes no difference to God at this hour. The land is utterly emptied and spoiled, it mourns and fades away, and it is defiled because its people have transgressed the laws, changed the ordinance, and broken the everlasting covenant. Because of this the curse devours the earth, its inhabitants are burned, and only a few are left alive. Where once billions filled the planet, only a remnant remains after Christ's coming, made up of Gentile survivors and the Jewish remnant who lived through the tribulation and the wrath of God.
Out of the destruction that follows the great war, the land itself must be cleansed. Weapons used in that final conflict are burned for seven years, and it takes seven months just to bury the dead so that the land can be made clean again, with a valley set aside for the burial of the enemy multitude. All of this marks the transition from the world's judgment into the peace of the Kingdom that Christ then establishes on the earth.
The scriptures
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: 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.
And the heaven departed as a scroll when it is rolled together; and every mountain and island were moved out of their places. And the kings of the earth, and the great men, and the rich men, and the chief captains, and the mighty men, and every bondman, and every free man, hid themselves in the dens and in the rocks of the mountains; And said to the mountains and rocks, Fall on us, and hide us from the face of him that sitteth on the throne, and from the wrath of the Lamb: For the great day of his wrath is come; and who shall be able to stand?
Behold, he cometh with clouds; and every eye shall see him, and they also which pierced him: and all kindreds of the earth shall wail because of him. Even so, Amen.
And I will pour upon the house of David, and upon the inhabitants of Jerusalem, the spirit of grace and of supplications: and they shall look upon me whom they have pierced, and they shall mourn for him, as one mourneth for his only son, and shall be in bitterness for him, as one that is in bitterness for his firstborn.
Behold, the LORD maketh the earth empty, and maketh it waste, and turneth it upside down, and scattereth abroad the inhabitants thereof. And it shall be, as with the people, so with the priest; as with the servant, so with his master; as with the maid, so with her mistress; as with the buyer, so with the seller; as with the lender, so with the borrower; as with the taker of usury, so with the giver of usury to him. The land shall be utterly emptied, and utterly spoiled: for the LORD hath spoken this word. The earth mourneth and fadeth away, the world languisheth and fadeth away, the haughty people of the earth do languish. The earth also is defiled under the inhabitants thereof; because they have transgressed the laws, changed the ordinance, broken the everlasting covenant. Therefore hath the curse devoured the earth, and they that dwell therein are desolate: therefore the inhabitants of the earth are burned, and few men left.
And they that dwell in the cities of Israel shall go forth, and shall set on fire and burn the weapons, both the shields and the bucklers, the bows and the arrows, and the handstaves, and the spears, and they shall burn them with fire seven years: So that they shall take no wood out of the field, neither cut down any out of the forests; for they shall burn the weapons with fire: and they shall spoil those that spoiled them, and rob those that robbed them, saith the Lord GOD. And it shall come to pass in that day, that I will give unto Gog a place there of graves in Israel, the valley of the passengers on the east of the sea: and it shall stop the noses of the passengers: and there shall they bury Gog and all his multitude: and they shall call it The valley of Hamongog. And seven months shall the house of Israel be burying of them, that they may cleanse the land. Yea, all the people of the land shall bury them; and it shall be to them a renown the day that I shall be glorified, saith the Lord GOD. And they shall sever out men of continual employment, passing through the land to bury with the passengers those that remain upon the face of the earth, to cleanse it: after the end of seven months shall they search. And the passengers that pass through the land, when any seeth a man’s bone, then shall he set up a sign by it, till the buriers have buried it in the valley of Hamongog. And also the name of the city shall be Hamonah. Thus shall they cleanse the land.
From the books
This answer is drawn from these passages in the Mary Banks Faith Library.