Marie Tharp Maps the Ocean Floor: Primary Sources in Three-Dimensional Science Learning

This blog post is by Jessica Fries-Gaither, a 2024-2025 Albert Einstein Distinguished Educator Fellow at the Library of Congress. It is one in a series exploring how to analyze primary sources through the three-dimensions of the National Research Council’s A Framework for K-12 Science Education and the Next Generation Science Standards.

What’s at the bottom of the ocean?

It hasn’t been that long since we were first able to answer that question. While sailors have traversed the ocean for centuries, many details of the ocean floor were a mystery until Marie Tharp and her colleague, Bruce Heezen, created a map of the ocean floor. Only then did we learn about features like the Mid-Atlantic Ridge, part of a 25,000-mile-long chain of ocean ridges spanning the globe. Tharp and Heezen’s work also verified Alfred Wegner’s theory of continental drift — the theory that the continents move over time in relation to each other and to Earth’s ocean basins.

By analyzing this primary source with a three-dimensional focus, students can learn about how Tharp and Heezen visualized the ocean floor and advanced the theory of plate tectonics.

Show students this manuscript painting of the Heezen-Tharp map and invite them to look closely. What do they notice? Which parts catch their eye first? What questions do they have?

After a preliminary analysis, invite students to dive deeper using guiding questions such as the following.

Disciplinary Core Ideas

• How is this map similar to other world maps you’ve seen? How is it different?
• What were Tharp and Heezen trying to show in this map?
• What was her purpose in creating this map?
• What new information does this map show?

Students may initially focus on the continents and say that the map shows the world. To help them identify the specific purpose of this map, ask them to compare it to other world maps or direct their attention to the map title. During discussion, listen for evidence of concepts related to the disciplinary core idea of plate tectonics, including the distribution of landforms on the ocean floor.

Science and Engineering Practices

• Which science and engineering practices might Tharp and Heezen have used to create this map?
• What data would Tharp and Heezen have needed to create a map like this? How could they have gotten this data?
• Why is a map more helpful than just raw data?

Students may need greater context during this portion of the discussion. Share information about Tharp and Heezen’s work on this project, including the sonar readings used as data. Listen for evidence that students are thinking about analyzing and interpreting data and developing and using models. You might also show students a list of the eight science and engineering practices to facilitate discussion.

Cross-Cutting Concepts

• Do you notice any patterns in this map? If so, what are they?
• Which other cross-cutting concepts might Tharp and Heezen have been thinking about as they created this map?

Analyzing the Heezen-Tharp map may also leave students with more questions than answers. When paired with other sources, such as this map of the seismicity of the earth, it can provide students with a foundational understanding of several sources of evidence for the theory of plate tectonics.