Primary Sources in Science Classrooms: Mapping the Ocean Floor, Marie Tharp, and Making Arguments from Evidence (Part 2)

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

In researching yesterday’s blog post on Marie Tharp’s maps of the ocean floor, I came across a number of related resources that address Earth science concepts.

Textbooks and teachers often tell students about German scientist Alfred Wegener who went public in 1912 with his theory of continental drift. The scientific community during Wegener’s lifetime did not widely accept the proposition that continents had shifted and often derided colleagues who entertained the theory. Even as Marie Tharp was creating maps in the 1950s, scientists were actively constructing ideas and compiling evidence related to seafloor spreading and magnetic striping.

One piece of evidence that influenced Wegener’s ideas about connected continents came from similarities among fossilized flora and fauna as well as geologic formations found on continents separated by oceans. While Wegener argued that continents were part of one large supercontinent, other scientists argued that land bridges facilitated the transportation of living things from continent to continent. These land bridges would have been in addition to the land bridge across the Bering Strait.

For instance, mentions of land bridges occur in:

• 1891 newspaper and 1896 newspaper articles, along with discussions about biodiversity;
• A 1900 map and notes suggesting a theory that Australia, Africa, and America were connected with Antarctica;
• An  article from 1901 similarly mentioning the possibility of continental connections with Antarctica.

Students, as they engage with current evidence that supports the modern theory of plate tectonics, might also benefit from evaluating some of the evidence and arguments put forth in newspaper articles from a century before. What evidence was being marshaled by scientists of the time to support their claims? How do the claims compare to today’s accepted theory about the continents? What evidence was missing that we have now? How does the evidence outlined in the articles support the now-accepted theory of plate tectonics—while also supporting the claims offered in the articles?

It is also worth pointing out that Wegener’s ideas about the complementary coastlines of North America, South American, Europe, and Africa were preceded by similar observations from Flemish cartographer Abraham Ortelius. Ortelius published the first comprehensive atlas of the world in 1570. A few decades later he wrote that the continents must have been joined in the past and had subsequently been separated by earthquakes and floods. As was the case with ocean floor maps that developed in the twentieth century, efforts to map the continents proceeded at a fast pace during the age of European exploration and geopolitical competition for resources. It took 400 years after Ortelius’s maps and writings for a complete theory of plate tectonics to emerge. The shapes of continents were only one piece of evidence to support our modern theory. Teachers might use this image as a starting point for discussions about how the theory has multiple parts and requires different pieces of evidence to arrive at an understanding of the mechanism that allows the continents to move.

Finally, students may wish to compare Tharp’s 1977 and 1982 maps to current maps of the ocean floor. The National Oceanic and Atmospheric Administration (NOAA) provide updated maps that display bathymetric data and data on natural hazards.

Special thanks to Tom Bober, the Library’s audio-visual Teacher in Residence, for his help with identifying resources about Marie Tharp, Alfred Wegener, and plate tectonics.