A mysterious layer of platinum discovered deep within Greenland's ice sheet, dating back approximately 12,800 years, was likely caused by a volcanic eruption in Iceland, not a meteorite impact as previously suggested. New research challenges the extraterrestrial origin theory for the chemical anomaly, proposing a more terrestrial explanation linked to the region's intense volcanic activity.
This finding has significant implications for understanding the cause of the Younger Dryas, a rapid cooling period that plunged the Northern Hemisphere back into near-glacial conditions. The study indicates the platinum deposit occurred after the cooling began, suggesting a large volcanic event, not a space impact, was the probable trigger for this major climate shift.
Key Takeaways
- New research suggests a platinum spike in Greenland's ice from 12,800 years ago originated from an Icelandic volcanic eruption.
- This contradicts the popular hypothesis that an asteroid or comet impact was the source.
- The study found the platinum deposit occurred 45 years after the Younger Dryas cold period began, ruling it out as the trigger.
- Evidence now points to a separate, massive volcanic eruption as the likely cause of the Younger Dryas climate event.
Revisiting an Ancient Climate Mystery
For years, scientists have debated the origin of a distinct platinum concentration found in an ice core from the Greenland Ice Sheet Project (GISP2). The discovery, dated to a period of abrupt climate change, provided compelling evidence for the theory that a cosmic impact triggered a millennium-long cold snap known as the Younger Dryas.
The Younger Dryas event, lasting from about 12,870 to 11,700 years ago, interrupted a post-ice age warming trend. Temperatures in Greenland plummeted by more than 15°C compared to today, and forests in Europe were replaced by tundra. A leading explanation has been that a massive release of freshwater from melting North American ice sheets disrupted ocean currents, causing the cooling.
What is the Younger Dryas?
The Younger Dryas was a period of sudden and severe cooling that occurred near the end of the last ice age. It represents one of the most well-documented examples of abrupt climate change in Earth's history, demonstrating how quickly the global climate system can shift between warm and cold states.
However, the 2013 discovery of the platinum spike offered an alternative trigger: a meteorite or comet fragment exploding over North America. This hypothesis gained traction, although the chemical signature in the ice was puzzling. Typically, extraterrestrial objects have high levels of the element iridium along with platinum, but the Greenland sample did not, leading some to propose the impactor was an unusual type of iron asteroid.
Searching for the Source on Earth
To investigate terrestrial sources, researchers first considered the Laacher See volcanic eruption in Germany, which occurred around the same time and was known for its unusual geochemistry. A new study involved analyzing 17 samples of volcanic pumice from the eruption's deposits to create a chemical fingerprint.
The results were definitive. According to the analysis, the Laacher See pumice contained almost no platinum. This effectively ruled out the German volcano as the source of the platinum found in Greenland's ice. This finding prompted scientists to look for other explanations.
Timeline Mismatch is Crucial
Using updated ice core dating methods, researchers determined the platinum spike began approximately 45 years after the onset of the Younger Dryas cooling. This chronological mismatch is a critical piece of evidence, as it means the event that deposited the platinum could not have been the trigger for the climate change.
Another key detail emerged from the ice core data. The elevated platinum levels persisted for 14 years. This duration is inconsistent with an instantaneous event like a meteorite impact but aligns well with a prolonged volcanic fissure eruption, which can last for years or even decades.
The Icelandic Volcano Hypothesis
With an impact event and the Laacher See volcano ruled out, researchers compared the ice core's chemical signature to other geological samples. The closest match was found in volcanic gas condensates, particularly those from submarine volcanoes. These are substances that form when hot volcanic gases cool and turn into liquids or solids.
"We compared the ice core's chemical signature with various other geological samples and found the closest match was with volcanic gas condensates... particularly from submarine volcanoes," explained James Baldini, Professor in Earth Sciences at Durham University, in an article for The Conversation.
Iceland emerged as the most likely location. During the period leading up to the Younger Dryas, the melting of massive ice sheets reduced pressure on the Earth's crust below Iceland, leading to a dramatic increase in volcanic activity. Eruptions that occur under glaciers or underwater interact with water in ways that can alter their chemical output.
How Volcanoes Can Create a Platinum Signature
- Interaction with Water: When magma erupts under ice or seawater, the water can strip away sulphur compounds from the volcanic plume.
- Element Concentration: This process can concentrate other elements, like platinum, in the remaining volcanic gases.
- Atmospheric Transport: These platinum-rich gases could then travel through the atmosphere to Greenland and be deposited onto the ice sheet over time.
This mechanism is supported by evidence from more recent Icelandic eruptions. For example, the Katla eruption in the 8th century produced a 12-year spike of heavy metals in Greenland's ice, while the 10th-century Eldgjá eruption caused a cadmium spike. These events demonstrate a clear precedent for Icelandic volcanoes delivering specific heavy metals to the Greenland ice sheet over extended periods.
A Different Volcano as the Climate Trigger
While the new research provides a strong explanation for the platinum mystery, it also reinforces that the platinum deposit did not cause the Younger Dryas. Instead, the study highlights other evidence pointing to a different, much larger volcanic event as the true culprit for the cooling.
Analysis of multiple ice cores reveals a massive spike in volcanic sulphate that coincides exactly with the start of the Younger Dryas, 12,870 years ago. This sulphate layer indicates a major eruption in the Northern Hemisphere—whether from Laacher See or another, still unknown volcano—injected huge quantities of sulphur into the stratosphere.
Volcanic Cooling Effect
Large volcanic eruptions can trigger global cooling by releasing sulphur dioxide into the stratosphere. The gas converts into sulphate aerosols that reflect sunlight back into space, reducing the amount of solar energy reaching the Earth's surface. This can initiate a cascade of climate feedbacks, including sea ice expansion and changes in ocean currents.
The timing of this massive sulphate injection, occurring when the climate was already in a delicate transitional state, may have been the nudge that pushed the Earth's system back into a cold, glacial-like condition. Understanding these past triggers is essential for preparing for future climate shifts, as major volcanic eruptions and meteorite impacts are low-probability but high-impact events that are certain to happen again.