Primary Sources in Science Classrooms: Mapping the Ocean Floor, Marie Tharp, and Making Arguments from Evidence (Part 1)

This post was written by Trey Smith, the Library of Congress 2015-16 Science Teacher in Residence. This is part one of a two-part post in anticipation of Earth Science Week.

What might a map from 1977, a poster from 1944, and a newspaper article from 1915 have in common with three twentieth-century wars and the theory of plate tectonics? These digitized artifacts in the Library of Congress’s collections have quite a bit in common when it comes to the emergence of evidence supporting a key theory in Earth science.

In this age of satellite imagery and maps on smartphones, it is easy to take for granted two- and three-dimensional representations of the Earth’s surface. However, the first full map of the ocean floor was not available until Marie Tharp, Bruce Heezen, and Heinrich Berann published their 1977 map.

In 1947, Tharp began converting data showing the changing depths of the ocean floor at various latitudes into a map that made plain the contours of the ocean floor. The data came from ships traversing the Atlantic Ocean at a time when Cold War tensions spurred interest and investment in safe and strategic submarine travel. Her work is an important example of science that does not involve experimentation in a lab, which is so often the focus of science classrooms and conversations. Marie Tharp donated her maps and notes to the Library of Congress in 1995.

Tharp’s map offers students an opportunity to look closely at seafloor structures, evidence of moving plates. A second map, published by Tharp in 1982, uses red dots to show the locations of major seismic events during the previous two decades. Instead of telling students what the maps show, teachers may offer the maps to students at the beginning of a lesson—or an Earth science unit—and ask them to make observations, reflections and questions.

• What do the maps show?
• What stands out?
• What prior knowledge do the students have about plate tectonics? (This could be ascertained without mentioning the key term.)

Support students’ reflections and questions with prompts such as:

• When, how, why, and by whom was the map created?
• What are the outlines on the map? And how are the outlines on the maps similar, different, and related?
• How are the maps themselves similar, different, and related?

For additional prompts and follow up activity ideas to help students engage with the map, consult the Analyzing Maps Teacher’s Guide.

The context in which Tharp created her maps also presents opportunities for interdisciplinary discussion and discovery. During World War II, the federal government, universities, and industry recruited women for roles that were traditionally reserved for men. Tharp pursued a geology degree as universities began admitting women into science and engineering programs previously open only to men.

Instead of providing students with a synopsis of the history of women in science and the changes that occurred as a result of World War II, use this poster as a starting point for student-driven background research: Students can make observations about the poster’s message and ask questions about the context in which the poster was created.

Gender politics cannot be ignored in the case of Tharp’s work. She was initially hired to perform secretarial duties in her lab, was not able to go on data-collecting vessels in the ocean for almost two decades into her career, and was insulted early on by her colleague Bruce Heezen when she pointed out that early maps of the Atlantic Ocean floor supported Alfred Wegener’s controversial ideas. (I will write more about the scientific community’s opposition to Wegener’s ideas in a follow-up post.)

Finally, teachers and students may be interested in considering the changes in technology that led to the mapping of the ocean floor. World War I hastened the development of sonar. Newspaper articles from 1915 describe at least one stage in this engineering timeline, heralding “the electrical ear” and claiming that submarines will be “rendered useless by new invention.” Modern sonar has advanced beyond the technology described in the article. However, it is clear that scientific understanding of sound was of keen interest during war time. Considering the collection methods introduces students to a example of research that does not follow the typical classroom model of an experiment. The newspapers can instigate further investigation and hands-on exploration. How does sonar work? What might students learn and wonder about sound after reading the articles?