Earth's Fossil History in Iowa's Rock Layers
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The Graf fossil site in Graf, Iowa, is a remarkable roadcut exposing distinct layers of rock (strata) packed with fossils from the Late Ordovician period. By observing these sedimentary rock layers and the diverse ancient marine life preserved within them, particularly abundant nautiloid cephalopods, students can investigate how scientists use evidence from rock formations and the fossil record to understand and organize Earth's vast 4.6-billion-year history.
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Graf
Iowa Core Standard
6-ESS1-4
Construct a scientific explanation based on evidence from rock strata for how the geologic time scale is used to organize Earth’s history.
Driving Question
- How do the rock layers and fossils at the Graf site serve as evidence to help us construct a scientific explanation of Earth's ancient history and the geologic time scale?
Probing Questions
- What specific types of fossils are found in the rock layers at the Graf site, and what do these ancient organisms reveal about the environment that existed in Iowa during the Ordovician Period?
- How do the alternating layers of limestone and shale visible at Graf provide evidence for changes in Earth's ancient sea over millions of years?
- How do scientists use the characteristics of rock strata and the fossils within them, like those at Graf, to determine relative ages and construct a chronological geologic time scale?
Classroom Suggestions
Students could:
- Investigate how scientists use the characteristics of rock strata and the fossils within them, like those at Graf, to determine relative ages and construct a chronological geologic time scale.
- Analyze the provided articles and visual evidence of the Graf site to identify specific features (e.g., fossil types, rock layers, their order) that serve as evidence to construct an explanation of Earth's history.
Resources
- Iowa PBS | FIND Iowa: Rock Layers and Fossils: This short educational video highlights the Graf fossil site. It provides information about the rock layers, geological history of Iowa, and information about the fossils found at the site.
- Virginia Museum of Natural History | Graf Fossil Site Research Article: This article explores the Graf fossil site, detailing how diverse Ordovician and Silurian fossils within specific rock layers (dolostones, limestones, shales) provide evidence. This evidence helps explain how scientists use rock strata and the fossil record to understand Earth's ancient history and the geologic time scale.
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