<P> Lithification (from the Ancient Greek word lithos meaning' rock' and the Latin - derived suffix - ific) is the process in which sediments compact under pressure, expel connate fluids, and gradually become solid rock . Essentially, lithification is a process of porosity destruction through compaction and cementation . Lithification includes all the processes which convert unconsolidated sediments into sedimentary rocks . Petrifaction, though often used as a synonym, is more specifically used to describe the replacement of organic material by silica in the formation of fossils . </P>

In the process of lithification which step happens first