A body buried in a wooden casket would decompose completely after a few hundred years, depending upon the conditions of the soil. Similarly, a seaman buried at sea would leave no traces. Not a trace seems to remain of all of those who went down with the HMS Titanic, for instance.
The apostle Paul made it clear that our new body, though having a great deal in common with our mortal body, will be a “spiritual body.” God will not need to gather up the scattered molecules of our earthly bodies. The bodies of many Christians and believers from before Christ have already decomposed, been completely destroyed by fire, or have been devoured by animals. Therefore, 1 Thessalonians 4:13-18 doesn’t require us to imagine a scene in which the ashes in funerary urns or decayed bodies in earthly graves are suddenly reconstituted. Rather, the resurrection is the wonderful occasion in which believers who have died will again be granted full bodily form, this time in a glorified body that can never again die or experience decay.
 1 Corinthians 15:35-44