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For example, most limestones represent marine environments, whereas, sandstones with ripple marks might indicate a shoreline habitat or a riverbed.Return to top The study and comparison of exposed rock layers or strata in various parts of the earth led scientists in the early 19th century to propose that the rock layers could be correlated from place to place.By matching partial sequences, the truly oldest layers with fossils can be worked out.By correlating fossils from various parts of the world, scientists are able to give relative ages to particular strata. Relative dating tells scientists if a rock layer is "older" or "younger" than another.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.
The first card in the sequence has "Card 1, Set A" in the lower left-hand corner and represents the bottom of the sequence.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.*Life Science: Fossils indicate that many organisms that lived long ago are extinct.Extinction of species is common; most of the species that have lived on the earth no longer exist.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.Scientists also use direct evidence from observations of the rock layers themselves to help determine the relative age of rock layers.Specific rock formations are indicative of a particular type of environment existing when the rock was being formed.Time factors of millions and billions of years is difficult even for adults to comprehend.However, "relative" dating or time can be an easy concept for students to learn.