1. Fossils

2. What are Fossils?
Fossils are the remains of plants or animals that lived a long time ago, or any evidence of their existence.

3. How can Fossils be Preserved?
Unaltered Preservation
Altered Preservation
Molds and Casts
Trace Fossils
unaltered preservation (like insects or plant parts trapped in amber, a hardened form of tree sap)
permineralization=petrification (in which rock-like minerals seep in slowly and replace the original organic tissues with silica, calcite or pyrite, forming a rock-like fossil - can preserve hard and soft parts - most bone and wood fossils are permineralized)
replacement (An organism's hard parts dissolve and are replaced by other minerals, like calcite, silica, pyrite, or iron)
carbonization=coalification (in which only the carbon remains in the specimen - other elements, like hydrogen, oxygen, and nitrogen are removed)
recrystalization (hard parts either revert to more stable minerals or small crystals turn into larger crystals)
authigenic preservation (molds and casts of organisms that have been destroyed or dissolved).

4. Unaltered Preservation
Insects that got stuck in tree sap were preserved unaltered.

5. Altered Preservation
The organism is preserved but its original skeletal material is altered by chemical changes.
Ex: petrified wood is no longer made of wood, it has actually turned stone.

6. Molds and Casts Molds Casts
A mold forms when something is pressed into soft mud and removed by decomposition or pulled out, leaving an impression of the object.
Casts
A cast is a 3-D representation of an object from the past. It is created when a mold fills up with sediment that hardens.
Molds and casts are actually two common types of trace fossils. A mold forms when something is pressed into soft mud and removed by decomposition or pulled out, leaving an impression of the object. A cast is a 3-D example of an object of the past created when a mold fills up with sediment like mud, sand or volcanic ash.

7. Trace Fossils
Trace fossils are indications that an organism existed, not the actual organism. They include footprints, nests, tooth marks, worm burrows, root traces, etc.

8. Where are Fossils Found?
What type of rock formation is this? Sedimentary, Metamorphic, or Igneous? Sedimentary, you can see the layers.

9. Why Sedimentary Rock?
The animal dies and lies on the ground or sinks to the sea floor.
The body begins to decay and is buried under layers of sediment such as mud or sand.
These layers eventually become sedimentary rock.

10. Examples of
Fossils

11. Sporadoceras http://www.imagesco.com/catalog/fossils/
Sporadoceras, which lived during the Devonian period 350,000,000 years ago, are extinct relatives of the chambered nautilus.  The shells of these creatures accumulated on the sea floor and were buried in sediment.  Over the ages they hardened to stone.  Today they are quarried from what is now the Sahara Desert in Morocco.

12. Nautilus

13. Orthoceras http://www.imagesco.com/catalog/fossils/
Orthoceras were marine, or sea animals similar to modern squid.  They had a shell shaped like a cone.  Orthoceras were active swimmers in warm shallow seas and swam by squirting water out of the body cavity.  They ate small animals and some grew to be 6 feet long.  In the fossilized remains of the shell, you can often see different chambers where the animal lived

14. Trilobites http://www.imagesco.com/catalog/fossils/
Scientists think that trilobites were the first multiple-celled animal to exist on earth.  These extinct sea animals had exoskeletons, or outer armor, that was divided into 3 parts.  Some crawled on the sea bed, some floated and some swam.  The lived all over the world.  Crabs and lobsters are modern relatives.

15. Fossil Fish http://www.imagesco.com/catalog/fossils/
Fish are the oldest and most primitive type of vertebrate.  The first fish were small, the size of a minnow.  They had heavy, bony plates for skin.  They lived on the ocean floor and are through slits on both sides of their throats.  Later, fish began to develop gills, scales and fins and learned to live in fresh water, too.  Some even developed lungs.  Over half the species of vertebrates, both living and extinct, are fish

16. Dinosaur Bone http://www.imagesco.com/catalog/fossils/
The word dinosaur means "terrible lizard".  Dinosaurs  were reptiles that lived throughout the world and dominated the land for over 140 million years.  Some were as small as a rooster in size.  Other grew to be the largest land animals ever to live and weighed up to 80 tons.  Many dinosaurs ate plants.  Others were meat eaters.  They began to die out when the Earth's climate became colder and plant life changed.

17. Brachiopods http://www.paxton-plts.org.uk
Brachiopods, commonly known as lamp shells, are filter-feeding coelomates enclosed in a bi-valved shell.
Brachiopods strongly resemble bivalve molluscs (clams, oysters, etc.), and the two are often confused.  The main external difference lies in the symmetry of their shells.
The brachiopod shell, in contrast with that of bivalve molluscs, consist of dissimilar dorsal and ventral valves (asymmetrical in profile), which are bilaterally symmetrical in plan view.
Brachiopods first appeared in the early Cambrian approximately 545 million years ago, and were the dominant benthic filter-feeders for most of the Palaeozoic Era.  They were hard hit by the mass extinction which defines the Permian/Triassic boundary about 245 million years ago.  It was shortly after this that bivalve molluscs came to dominate this ecological niche.
Brachiopods still persist today, but are neither abundant nor diverse.  There are approximately 325 species of living brachiopods, which is a pale shadow of their former diversity of more than 12,000 described fossil species.

18. Echinoderms http://www.viaccess.net/~jacaroe/star.jpg
A nyone who has been to the beach has probably seen starfish or sand dollars. The more intrepid beachcomber may find brittle stars, sea cucumbers, or sea urchins. These and many other organisms, living and extinct, make up the Echinodermata, the largest phylum to lack any freshwater or land representatives.
Most living echinoderms, like this sand dollar from Baja California, are pentameral; that is, they have fivefold symmetry, with rays or arms in fives or multiples of five. However, a number of fossil echinoderms were not pentameral at all, and some had downright bizarre shapes. Echinoderms have a system of internal water-filled canals, which in many echinoderms form suckered "tube feet", with which the animal may move or grip objects.
echinodermata.html

19. Chrinoid Stems
Crinoids belong to the animal kingdom and are related to Star Fish (Echinoderms).  A growing crinoid looks very plant like, a long stalk attached to the ocean floor with a flower like top.  They are commonly called Sea Lilies.  This piece of limestone contains numerous crinoid stems, the disks that the crinoid stalk is composed of. Note the 5 sided "star" in the center of each disk - Star Fish have five arms. Period: Middle Ordovician, 450,000,000 years

20. Coral Fossils
Corals are part of a group of animals called Cnidaria (nid-AIR-ee-a), also called Coelenterata (sel-EN-ter-AH-ta), which includes sea anemones, corals, jellyfish, and hydras. All of these animals are soft bodied and have multiple arms or tentacles, with which they grab food from the surrounding sea water. All Cnidaria (including corals) live in water and most are marine animals. The soft, jelly-like body of an individual cnidarian animal is called a polyp.
A comprehensive group equivalent to the true C[oe]lenterata, i. e., exclusive of the sponges. They are so named from presence of stinging cells (cnidae) in the tissues.
n : hydras; polyps; jellyfishes; sea anemones; corals

21. Plant Fossils

22. Snails and Slugs
Any of various mollusks of the class Gastropoda, such as the snail, slug, cowrie, or limpet, characteristically having a single, usually coiled shell or no shell at all, a ventral muscular foot for locomotion, and eyes and feelers located on a distinct head.
One of the classes of Mollusca, of great extent. It includes most of the marine spiral shells, and the land and fresh-water snails. They generally creep by means of a flat, muscular disk, or foot, on the ventral side of the body. The head usually bears one or two pairs of tentacles. See Mollusca. [Written also Gasteropoda.] Note: The Gastropoda are divided into three subclasses; viz.: ({a}) The Streptoneura or Dioecia, including the Pectinibranchiata, Rhipidoglossa, Docoglossa, and Heteropoda. ({b}) The Euthyneura, including the Pulmonata and Opisthobranchia. ({c}) The Amphineura, including the Polyplacophora and Aplacophora.

23. Now it’s time to make a fossil mold and cast!

24. Fossil Molds
Sometimes you find a fossil mold of a shell, like this one. Depending on the shape of the mold, it is sometimes possible to make a cast of the shell.

25. Making a Cast
By filling the mold with plaster, a cast of the fossil can be made. In nature, sediments would fill the mold and eventually harden, also forming a cast.

26. The Cast When the plaster dries
it can be separated from the mold, resulting in two types of fossils, a mold and a cast.