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These major concepts are part of the Denver Earth Science Project's "Paleontology and Dinosaurs" module written for students in grades 7-10.The module is an integrated unit which addresses the following National Science Education Standards: *Science as Inquiry: Students develop the abilities necessary to do scientific inquiry — identify questions, design and conduct scientific investigations, use appropriate tools and technologies to gather, analyze and interpret data, think critically and logically to make the relationships between evidence and explanations, communicate results, and use mathematics in all aspects of scientific inquiry.

INTRODUCTION Scientists have good evidence that the earth is very old, approximately four and one-half billion years old.

Scientific measurements such as radiometric dating use the natural radioactivity of certain elements found in rocks to help determine their age.

The Law of Superposition, which states that in an undisturbed horizontal sequence of rocks, the oldest rock layers will be on the bottom, with successively younger rocks on top of these, helps geologists correlate rock layers around the world.

This also means that fossils found in the lowest levels in a sequence of layered rocks represent the oldest record of life there.

If certain fossils are typically found only in a particular rock unit and are found in many places worldwide, they may be useful as index or guide fossils in determining the age of undated strata.

By using this information from rock formations in various parts of the world and correlating the studies, scientists have been able to establish the geologic time scale.The fossils represented by the letters on this card are "younger" than the "T" or "C" fossils on the "TC" card which represents fossils in the oldest rock layer.Sequence the remaining cards by using the same process.*Earth and Space Science: Fossils provide important evidence of how life and environmental conditions have changed.The complete "Paleontology and Dinosaurs" module takes approximately four weeks to teach. " activity is a 30-minute introduction to geologic time.*Life Science: Fossils indicate that many organisms that lived long ago are extinct.