242 A HISTORY OF AMERICA IN 100 MAPS
In 1912 the German geophysicist Alfred Wegener
theorized that the world’s continents—initially bound
together as a single landmass—were slowly drifting
apart. Wegener’s idea of continental drift was initially
met with skepticism, but research into the contours
of the ocean floor at mid-century supplied intriguing
evidence for this theory. By the late 1960s, earth
science had been fundamentally transformed by the
theory that the earth was a system of dynamic oceanic
and continental plates interacting with one another.
This glorious profile of the ocean floor helped to
explain this emerging framework of plate tectonics.
The Atlantic seabed was four times the size of the
United States, yet until the 1950s it remained more
mysterious than the surface of the moon. Research
into the ocean floor stretched back to the nineteenth
century, but accelerated significantly only after
World War II. Some of this was conducted by Bell
Labs, which was constructing the first transatlantic
telephone cables, from Newfoundland to Scotland.
At the same time, the development of nuclear
submarines in the early Cold War necessitated a more
precise understanding of oceanic depths, which was
made possible by advances in sonar technology.
Much of this new research was undertaken at
Columbia University’s new Lamont Geological
Observatory, and sponsored by both the Office of
Naval Research and Bell Labs. There, geologists Bruce
Heezen and Marie Tharp collaborated to develop a
new picture of the ocean floor. In the 1950s, Heezen
organized several Atlantic expeditions to generate
soundings, and integrated these with existing data
from Bell. Despite her advanced degree in geology,
Tharp was not permitted to join these expeditions
because she was a woman. Yet she played a crucial
role in analyzing and synthesizing the data.
Tharp was well equipped for the task. As a child
she had traveled extensively with her father, a
surveyor for the Department of Agriculture, which
exposed her to both mapping and fieldwork. Back
at Columbia, she plotted Heezen’s soundings into
CONTINENTAL DRIFT
Heinrich Berann and the National
Geographic Society, “Atlantic Ocean
Floor,” based on studies by Bruce
C. Heezen and Marie Tharp, 1968
rows, and then organized these into profiles. In the
process she began to notice a V-shaped rift within the
Mid-Atlantic Ridge that ran from north to south along
the basin. This led her to posit that the sea floor was
acting against itself, with landmasses moving apart in
a way that supported Wegener’s theory of continental
drift. The German oceanographer Günter Dietrich
had made similar observations in the 1930s.
Armed with this new data and existing theories,
Tharp and Heezen began to develop a picture of
the rifts and ridges of the ocean floor that advanced
theories of continental drift. The shape of the ocean
floor mattered.
It was Tharp who translated the data into a
coherent profile. Her initial map of 1957 was
published in Bell Laboratory’s technical journal, as
it had important implications for communications
technology. This early iteration of the map was in fact
the first to present the Mid-Atlantic Ridge and the rift
within it, which formed a crucial piece of evidence
for continental drift. Ten years later, the National
Geographic Society hired not a cartographer but an
artist to visualize this new research for the public.
The Austrian painter Heinrich Berann skillfully
presented a comprehensive—if still speculative—
picture of the entire Atlantic Ocean floor. Building
on decades of research, Berann depicted the seabed
in a way that both exposed its complexity and also
helped to explain and advance the dynamics of plate
tectonics. This was not just an illustration of the
ocean floor, but a preliminary explanation of a new
geological theory.
The image revealed the full extent of the Mid-
Atlantic Ridge. It also identified the transform
faults that cut horizontally across the ridge, where
two plates slid past one another. Together, these
topographic features formed a crucial piece of
evidence for plate tectonics. Berann’s view of the
ocean floor was necessarily general, for the data was
itself incomplete: more suggestive than conclusive.
Yet much of it would be confirmed within a few years
by American and British research. By the late 1960s,
Heezen and Tharp had published profiles of all the
ocean floors, each of which helped to complete
the picture of plate tectonics. Like the “Earthrise”
photograph on the next page, these images were a
geographical revelation. Equal parts science and art,
evidence and speculation, they both visualized a new
scientific theory and unveiled the last great unknown
reaches of the earth.