Rock Cycle - Past Life (2A)
Pre Lab 

  • Exploring how fossils are made.
  • Comparing present day and fossil organisms.
  • extinct
  • fossil
  • preserved
  • fossil shell and a present day shell
  • extinct animals

Students compare living and fossil shells.


Fossils are the remains of plants and animals that lived long ago. Most fossils were formed when the hard parts of an animal were buried in soft mud, silt, or sand. Over thousands of years the original bone, wood, or shell decayed or dissolved away, but its shape was preserved by minerals that seeped in and replaced the original material. Sometimes a fossil organism can be preserved exactly as it was when it died. This is very uncommon.

There are two main types of fossil preservation, without and with alterations. Most common is fossil preservation with alteration. This is when the original organic material is partially to fully changed into new material. Types of preservation with alteration include carbonization, permineralization, recrystallization, and replacement.

The second type of fossil creation is direct preservation, the preservation of fossils without alteration. The most common directly preserved fossils are unaltered hard parts of a living organism, like shells, teeth, and bone. This material is unchanged, except for the removal of less stable organic matter. Examples of this type of preservation include fossil corals, shells, sponges, microscopic fossils and a host of other organisms with hard parts. In rare circumstances, preservation of the soft parts of an organism may occur. An example is Dimo, a baby mammoth found in the tundra of Siberia. The ice "froze" all the body parts. The preservation was so good that paleontologists were able to determine that the baby mammoth died of blood poisoning. Another example is an insect which has become "stuck" in tree resin. When the resin fossilizes to form amber it preserves the insect. This was the whole premise for the book and  movie called  "Jurassic Park."


  1. Show the students a fossil and its present day equivalent. Students should compare degree of preservation, color, texture, and any other characteristics that they see.

  2. Emphasize that fossils do not represent the entire animal, so paleontologists (scientists who study fossils) must to be very careful when making conclusions about the original living organism.

  3. Discuss with your students that there are many types of fossils, representing many kinds of organisms. Not all fossils that we find represent extinct organisms. Dinosaurs are extinct, but sharks and clams are not. The living representatives of sharks and clams still look similar to the fossils that their ancestors left behind. Lead the students into a discussion concerning the following fossils, and talk about whether the specimens represent extinct animals (referring to the organism as a group, not as an individual species) and what part of each organism might or might not be preserved in the form of a fossil. Use the following diagram to guide you.






bones, teeth






outer shell

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