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If the Greenland Ice Sheet were to melt entirely, global sea levels would rise by seven meters, an outcome that would dramatically affect coastlines and societies around the world. A long-lost sediment core recovered from a secret Cold War-era U.S. military camp in Greenland revealed compelling evidence that Greenland was once ice-free. By unlocking the past, scientists uncover urgent clues about our future. The finding that the ice sheet melted in the past completely transforms our understanding of the stability of the Greenland Ice Sheet. The research itself is detailed in a comprehensive paper in Science. The film was funded by the National Science Foundation as a collaborative research grant across multiple academic institutions and highlights cutting-edge science.
The sediment core from Camp Century contain more than just soil, they also hold remnants of ancient plants and organic materials. Thousands of meters below ice, life once flourished. Camp Century's long lost core reveals fossilized plants, seeds, and insects that could only have thrived in freshwater streams surrounded by luscious vegetation. Using cutting-edge techniques and fossils as a window into the past, scientists determined not only that this area was ice-free 400,000 years ago, but also the climate was very similar to what it is today.
The Science of Sediment
Dating
Geologists and paleoclimatologists use two different types of dating to determine how old ancient materials are: Relative dating and absolute dating. Relative dating is a technique that allows scientists to establish a chronological order of events, such as rock formation or fossil deposition. It can help determine what is older versus what is younger without assigning numerical values to their age. Absolute dating is a more precise dating technique that assigns materials an actual age. Two techniques used on the Camp Century core are luminescence dating and cosmogenic nuclide dating.
An example of relative dating is using stratigraphic records of sediment cores to compare layers. Each layer in the core represents a snapshot of the environment when it was deposited, with the youngest being the topmost layer and the oldest being at the bottom. The scientists investigate the layers of sediment deposited, giving inherent clues about the past. Within the sediments, scientists discovered fossilized plants, indicating a period when this part of Greenland was ice-free. The film then dives into the mystery of when the land last saw the light…
One way we can scientifically understand when the land last saw the light (or when the ice was gone) is through Optically Stimulated Luminescence (OSL). It works a bit like a resettable clock, in grains of sand or quartz. When exposed to sunlight, the clock resets, and once buried, it starts ticking again. By measuring the faint glow these grains release in the lab, scientists can tell when they were last at the surface, or not covered by ice. They determined that the top sediment layer was last at the surface about 400,000 years ago.
Cosmogenic nuclide dating measures rare isotopes formed when cosmic rays from space strike rocks at Earth’s surface. Once buried under ice, the “cosmic clock” stops. By checking how much of these isotopes remain, researchers can figure out how long the land was exposed before it was covered again. Together, these methods revealed that Greenland was ice-free long enough for plants to grow where today a thick ice sheet stands.
The Greenhouse Effect
The Greenhouse Effect is Earth’s natural heating system. When sunlight enters the atmosphere, some of it warms the land and oceans, while some reflects back toward space. Greenhouse gases—like carbon dioxide, methane, and water vapor—act like a blanket around the planet. They trap part of this heat and keep Earth’s temperature stable enough for plants, animals, and people to survive. Without this effect, Earth would be far too cold to sustain life.
The problem today is that human activities, such as burning fossil fuels and cutting down forests, are adding extra greenhouse gases to the atmosphere. This makes the greenhouse effect stronger than it should be, trapping more heat than the Earth can handle. As a result, global temperatures are rising, ice sheets and glaciers are melting, and sea levels are climbing—changes that threaten ecosystems and communities worldwide. If we don’t stop this, our greenhouse will become a hothouse, with temperatures never seen by our human species before.
Human carbon dioxide emissions have been exponentially rising since the industrial revolution.
Eunice Newton Foote’s Warning
Eunice Newton Foote, a female scientist in 1856, presented evidence carbon dioxide could warm Earth’s atmosphere. She found that when filling cylinders of different gases (moist air, dry air, carbon dioxide, oxygen, and hydrogen) and heating them up in the sun, the one with carbon dioxide increased in temperature the most and took significantly longer to cool down. This is the basis of the greenhouse effect.
A male colleague presented this research for her (since she was not allowed) at the American Association for the Advancement of Science (AAAS). Though her findings were then scooped by John Tyndall three years later, Eunice Newton Foote is the founder of modern climate science.
The film draws a line from her early warnings to today’s cutting-edge research as scientists reconstruct an ancient, greener Greenland when atmospheric CO₂ was half of today’s levels. Through innovative methods, from cosmic ray exposure dating to forensic botany and chemical analysis of ancient leaf waxes, researchers now know the Greenland Ice Sheet has collapsed before and their findings show it is on track to melt again.
After seeing the film, The Memory of Darkness, Light, and Ice, California Senator Ben Allen recognized Eunice Foote’s contributions to modern climate science and named July 17th, her actual birthday, as Eunice Newton Foote Day in California. Watch the video!
Camp Century, a city under the ice
Camp Century was built by the U.S. Army Corps of Engineers in 1959, during the height of the Cold War. Hidden beneath the surface of the Greenland ice sheet, the camp consisted of a network of snow tunnels, barracks, labs, and even a chapel and a hobby shop, all powered by one of the world’s first portable nuclear reactors.
Officially, it was presented as a scientific outpost, but behind the scenes it was part of Project Iceworm, a secret plan to test whether nuclear missiles could be stored and launched from beneath the ice. The extreme conditions, shifting ice, collapsing tunnels, and the sheer difficulty of maintaining life under the glacier, meant the project was never completed.
By 1967, Camp Century was abandoned. Today, it’s remembered as both a Cold War experiment and the unlikely birthplace of modern ice-core science.
Explore the film
Isotope geochemists Andrew Schauer and Eric Steig examine samples showing warming of the past climate.
Andrew Christ on time capsules of geologic time.
Secrets in cores: What can seeds tell us about past climates?
Paleoecologist Dorothy Peteet’s extensive seed collection can help understand sediment fragments.
Master’s student Halley Mastro identifies flies in sediment.
“The question is not whether we are changing the climate and warming the planet. The real question is: how fast are Greenland and Antarctica melting?”
— Dorthy Peteet, Paleoecologist