Earth Science: Studying Fossils

Introduction:
In this lesson, we will study fossils. Where did they come from? How are they made? What can we learn from them? How do we identify and classify them? These are just some of the questions we will answer in this lesson.

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Print the Fossils activity worksheets.

1. For an introductory background to fossils, check the Royal Ontario Museum Web Site: http://www.rom.on.ca/quiz/fossil/. Review this material with the group.

2. Show and discuss the sample fossils provided with the lab: These samples were purchased from WARD's Natural Science Establishment, Inc., Rochester NY. (Fossil Display Pack 50 E 0115) Most of the definitions given below either are from the material provided with the samples or were obtained from the Royal Tyrrel Museum Fossil Encyclopedia at: http://tyrell.magtech.ab.ca/encyclo/t.html.

A) Horn coral:
A coral found only in Paleozoic rocks and no longer exists in our present oceans. This fossil is about 375 million years old.

B) Bryozoan ("moss animals"): These small aquatic animals. average less than 1 millimeter in length but live in large colonies that are as much as 30 cm across.

This is approximately 12 inches -- the length of a standard ruler. Modern bryozoans are found in warm shallow seas, where they grow attached to the sea floor.

C) Brachiopod ("lamp shells"): Brachiopods are a common type of shellfish found in marine rocks from early in the Cambrian period onwards, and they have survived to the present today. They had two shells and lived attached to the sea bottom. There are around 200 living species of brachiopod, and around 30,000 species of fossil brachiopods. Brachiopods still exist today but are very rarely found as seashells on the beach.

D) Gastropod ("snails"): This typical snail shell has a spirally coiled, single-valved shell. These mollusks first appeared about 550 million years ago, and exist today both on land and in water. This example is about 100 million years old.

E) Trilobite ("three lobed"):.
Trilobites are arthropods related to the modern horseshoe crab. They were especially abundant during the Cambrian Period and became extinct during the end of the Permian Period (225 million years ago). A trilobite molted its exoskeleton periodically as it grew, so it is possible that one trilobite could produce many fossil remains. From Doug DeRosear's Fossil Collection (http://burlingtonia.miningco.com/library/bltrilobite.htm).

F) Shark tooth: This tooth is a fossil remnant of a shark, which lived some 20 million years ago. Sharks have evolved nearly 350 million years, and have changed little during this period.

G) Crinoid Stem ("sea lilies"): Crinoids live in groups. Complete crinoids are rarely preserved as fossils since the plates that make up the animals hard parts fall apart at death. These animals are abundant and important from the Ordovician to the Tertiary.

Most of them, both fossil and living species, have long stalks that anchor them to the bottom. Attached to the stalk is a cup in which the main body organs lie. The mouth lies at the center and five or more arms channel food towards the mouth.

H) Petrified Wood: Petrified wood is created in a similar process as the animal fossils already seen. About 225 million years ago, trees in an ancient forest fell down and were washed downstream into a floodplain. Here they were buried by volcanic sand

and silt sometimes to a depth of 1100 feet. Over time, the wood was replaced by silica that was carried by the water. What we see today is a 'rock' that is the same shape and size as the original piece of wood. The beautiful colors are caused by other minerals that are mixed with the silica. For more information check out the Petrified Forest, National Park Web Site.