How are casts formed by decaying organisms?

impression left by organisms are filled in with sediment

Explaination:        Cast fossils are produced when an organism decays and is buried between layers of mud and silt. The mud and silt from nearby what is left of the organism and gradually hardens and converts into sedimentary rock.  The buried organism decays and the hardened rock leaves an impression where the organism once was.  Finally, mineral-enriched groundwater fills in the mold and solidifies to form a cast fossil

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Explanation:

answer; i thinking 4.5 million. in sydney australia;

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