Fourth Grade Students Investigate Stratigraphy through Experiments and Photographs of Snow Layers

Article excerpt

ABSTRACT

This article describes a project in which fourth graders investigated principles of stratigraphy by creating colored sand layers in a clear-sided container and observing photographs of cross sections of snow layers and rock outcrops along roadsides. Students used the National Science Education Standards unifying concept of "evidence, models, and explanations" to investigate stratigraphic principles of original horizontality, superposition, and crosscutting relationships. A pretest/posttest evaluation of the lessons showed that students learned basic concepts of stratigraphy.

INTRODUCTION

Childhood activities can affect a student's decision to study science (Edgett, 1998; Rule, 2001). Filling small bottles with layers of colored salt-sand was a favorite pastime for children in my neighborhood during the 1960's. We made the "sand" by spreading a newspaper page on the sidewalk, dumping a small mound of salt on the newspaper, then rubbing it with the broad edge of a piece of colored chalk, storing each batch in a jar. Friends paid for a bottle of salt with a penny or safety pin, specifying each layer, color by color, until the container was full. Because this was one of the memorable childhood activities that lead to my becoming a geologist, we decided to incorporate a similar activity in the stratigraphy investigation we describe here for elementary students.

So many things in the natural world (lava flows, soils, lake sediments, snow banks) and designed world (cakes, sandwiches, roadbeds, house walls, bed coverings, winter or sports clothing) exhibit layers. Many scientists (paleontologists, vulcanologists, archaeologists, among others) interpret the relationships between layers to help in professional problem solving. Stratigraphy, the study of the order and relative positions of strata, depends upon these principles: the Principle of Original Horizontally, which states that because of gravity, sediments are deposited in horizontal beds; and the Principle of Superposition, that states in a sequence of horizontal layers, those near the bottom are older than top layers.

In this article, we describe how fourth graders in New York State explored stratigraphy concepts with colored sand layers and photographs of multi-storm snow banks. Oswego County on the shore of Lake Ontario regularly receives large snowfalls each winter because of the great lake's effect. During the winter of 2003-2004, the city of Oswego received over five meters of snow in a series of storms and almost-nightly snowfalls. After each storm, trucks sprinkled gravel, sand, clay and salt on the roads, which was added to the snow banks by snowplows. As snow banks towered two or three meters high, the city used a large snowblower to slice and trim them to widen the road surfaces. The resulting flat faces of these snow banks provided an interesting record of the different snowstorms, sanding/plowing events and homeowner shoveling attempts. We decided to use snow bank photographs to present stratigraphic concepts to our fourth graders as this provided a strong link to familiar real-world experiences.

Standards Applied to Snow Bank Stratigraphy - The Benchmarks for Science Literacy (American Association for the Advancement of Science, 1993) under chapter 4, The Physical Setting, Part C, Processes that Shape the Earth, state, "By the end of the 5th grade, students should know that waves, wind, water, and ice shape and reshape the earth's land surface by eroding rock and soil in some areas and depositing them in other areas, sometimes in seasonal layers." In this investigation of the stratigraphy of seasonally deposited snow banks, students learn how to interpret the relative ages of layers of snow with crosscutting relationships and make connections to other sedimentary strata. Also, the New York State Science Curriculum Standards (the state in which this study took place), under Standard 4 of Science for Elementary Grades, the Physical Setting Standard 2 (University of the State of New York State Education Department, 2003) states, "students should be able to describe the relationships among air, water, and land on Earth. …