Tafsir of Qaf 50:4

{We know what} This is a refutation of their disbelief in the resurrection. For He whose knowledge is so subtle that it penetrates into what the earth consumes of the bodies of the dead—their flesh and their bones—is surely capable of returning them to life just as they were.

It is narrated from the Prophet (ﷺ): "Every son of Adam decays except the tailbone (coccyx)."

Al-Suddi said regarding {what the earth consumes of them}: It refers to those who die and are buried in the earth.

{A preserved record} It is protected from the devils and from alteration; it is the Preserved Tablet (al-Lawh al-Mahfuz). Or, it is a "preserver" of what has been deposited and written within it.