Turtle Shells Keep a Record of Humanity’s Nuclear History, Provides Clue on the Effect of Warfare and Energy Production in the Future

In 1978, a fisherman caught a tiger shark in a lagoon located in the Marshall Islands in the North Pacific. The shark ended up in a natural history museum with the remains of a green sea turtle it had swallowed. Experts realized that this turtle holds clues to the past nuclear activities in the area and may help them understand the impact of nuclear research in the future.

(Photo: Wikimedia Commons/ Michael Rivera)

Signs of Nuclear Activities

In 1952, the first hydrogen bomb test destroyed an island in the North Pacific. It is one of the 43 nuclear bombs detonated at Enewetak Atoll during the early years of the Cold War. Archeologist Cycler Conrad from the Pacific Northwest National Laboratory investigated whether chelonian species such as turtles, tortoises, sea turtles, and freshwater terrapins had recorded the radioactive materials from these explosions. They focused on animals that potentially accumulated anthropogenic uranium through nuclear fallout or waste.

Conrad collaborated with experts from Los Alamos National Laboratory, where he used some of the world's most advanced tools for detecting radioactive elements. From the result of their study, it was found that turtles and other animals that had lived near the nuclear development sites carry highly enriched uranium in their shells. This evidence serves as a telltale sign of nuclear weapons testing.

Turtles as Record-Keepers

There are turtles at any site of a nuclear event, not because they are drawn to them but because they are just everywhere. Since the dawn of recorded history, these animals have been the mainstays of mythology and popular culture. In other words, the story of humans on the planet is closely tied to turtles. Since these reptiles are known for having long lifespans, they can document the story of human activities within their tough, slow-growing shells.

The turtles' shells are covered by a scute, a bony external plate made of keratin. The shield-like scale is overlaid with a horn and can also be found on the skin of some reptiles like crocodiles and birds' feet.

Scutes grow in layers like tree rings. Beautiful swirls that preserve a chemical record of the environment are formed in each sheet layer. If an animal takes in more chemicals than it can excrete, that chemical substance will stay in its body.

Once these chemicals enter the scute, they are stuck there. The contaminants can get smeared across layers of soft animal tissue, but they also get locked into each scute layer when the turtle is exposed. The growth pattern on the shell depends on the turtle species. For instance, box turtles grow their scute outward like human fingernails grow over time. On the other hand, desert tortoises also grow their scute sequentially, but new layers grow underneath older layers and create a tree ring-like profile.

Turtles have long been considered the sentinels of ecosystem health due to their sensitivity to environmental changes. While they show things that are emergent problems, they can also reveal things that are distinct problems from the past.