Academic journal article The Science Teacher

William Smith's Mapping Milestone: An Interactive Historical Vignette Celebrating the Bicentennial of the First National Geologic Map

Academic journal article The Science Teacher

William Smith's Mapping Milestone: An Interactive Historical Vignette Celebrating the Bicentennial of the First National Geologic Map

Article excerpt

Two hundred years ago, in 1815, English geologist William Smith (1769-1839) produced the first geologic map of a country. Covering more than 175,000 km (2), it included England, Wales, and part of Scotland (Sharpe 2015). The map is impressive for its scope and sheer size--covering 2.6 m x 1.8 m of wall space at the Geological Society of London's Burlington House. Most importantly, the Smith map (opposite) is important for its method--using distinctive fossils to correlate strata over large areas--which changed how people envisioned and mapped Earth's subsurface.

The history of Smith's innovations reveals cultural constraints of the early 1800s: Gentlemen of social status could theorize about the Earth, but women and the working class were effectively barred from the elite intellectual societies. Of humble origins himself, Smith lamented in 1816 that the theorizing of geology was done by one class of men but the practice by another (Woodward 1907). As a working-class, self-taught surveyor, Smith innovatively visualized and mapped the geological strata of his country, hoping to find future coal fields for an early industrialized England. Smith creatively used fossil organisms to correlate rock layers and put them into their correct order. "Strata" Smith is often called the Father of English Geology and the Father of Stratigraphy.

William Smith's mapping milestone has had far-reaching implications. Even today, exploration for fossil fuels and other natural resources begins with a detailed geologic map.

Geological interpretation: Relative age-dating strategies

William Smith mapped the geologic rock units (large rock bodies of similar composition and characteristics) as surface exposures on his large map, and he also provided eight geological cross sections that showed what happened to the rock layers below the surface, such as tilting and folding. Even before Smith started mapping England's countryside, several principles of relative age dating had been developed that could help determine the age and order of strata. In the 17th century, Danish scientist Nicolas Steno (1638-1686) recognized that the oldest rock layers lie at the bottom of a rock outcrop, a tenet now known as the principle of superposition (Figure 1, p. 38). Steno also recognized that sediments were originally deposited horizontally, so tilted rock layers must have been acted upon by some force after the sediments were deposited and lithified (principle of original horizontality). Sediments are deposited continuously until the supply pinches out (principle of lateral continuity), and any igneous intrusion that cuts across rock layers, or a fault that displaces rock layers, must have happened after the layers were deposited and lithified (principle of cross-cutting relationships). The order of events in a rock outcrop can be determined with these basic principles of relative age dating (Figure 2).

Smith's investigations added an important tool to relative dating methods and interpretation of cross sections. Smith recognized that certain layers of rock contained distinctive fossil groups (Figure 3), always in the same order. Smith developed the principle of fossil succession that allowed him to order rock layers based on what fossils they contained. Therefore, even if two rock units looked the same, Smith could tell them apart (Torrens 2001).

Interactive historical vignettes

An effective vehicle to introduce William Smith to science classrooms, engage students in the nature and history of science, and promote scientific habits of mind is the Interactive Historical Vignette (IHV), a short scripted play or monologue that involves students in a brief episode in the life of a scientist.

Though requiring minimal classroom time, IHVs can pique student interest and engage the classroom in predicting how the story will conclude. IHVs focus on a single facet of the nature of science, such as a historical scientist's thirst for knowledge; willingness to change an opinion with evidence; skepticism; or respect for the power of a theory (Roach and Wandersee 1993; Wandersee and Roach 2005). …

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