About 12,900 years ago, the Northern Hemisphere was warming out of the last Ice Age when it was suddenly thrown back into near-glacial cold. That cold snap, the Younger Dryas, lasted roughly 1,200 years. It coincided with the disappearance of mammoths, mastodons, and other large animals across North America, and with the end of the Clovis culture.

Nobody disputes that the Younger Dryas happened. The argument is about what started it. In our earlier article we laid out the main contenders. This piece takes stock of what changed in 2026, a year that brought new evidence, a new rival explanation, and two high-profile retractions. We have tried to score it the way a careful juror would: on the strength of the evidence, not the excitement of the story.

The Three Explanations

  • Meltwater. The most widely accepted explanation. A huge pulse of fresh water from melting North American ice sheets poured into the North Atlantic, weakening the ocean currents that carry heat north. Cooling followed.
  • Cosmic impact or airburst. The Younger Dryas Impact Hypothesis, first proposed in 2007, holds that fragments of a comet struck or exploded above the Earth, setting off wildfires, darkening the sky, and possibly destabilizing ice sheets. Supporters point to markers in a thin sediment layer at the Younger Dryas boundary: tiny melted spheres, platinum spikes, nanodiamonds, and melt glass.
  • Volcanism. A major volcanic episode loaded the atmosphere with aerosols that reflected sunlight, tipping a fragile climate into cold.

These are not entirely exclusive. An impact or an eruption could, in principle, have triggered the meltwater pulse. But the debate is mostly about the trigger.

The Case For an Impact in 2026

Greenland. A study led by James Kennett, Paul Mayewski, and colleagues examined a sequence of sediments at the edge of the Greenland ice sheet near Kangerlussuaq, spanning the transition into the Younger Dryas. The authors concluded that the record is consistent with a short, high-energy airburst or impact event, possibly a major trigger of the cooling. They tied it to an earlier finding from the GISP2 Greenland ice core: a platinum anomaly at the onset of the Younger Dryas, with a peak spread over about 21 years, which they interpret as impact material settling gradually rather than all at once. The study appeared in Airbursts and Cratering Impacts in 2026.

Sweden. In October, a team led by Christopher Moore of the University of South Carolina reported a new sediment core from southern Sweden. It shows a layer of ash from the Laacher See volcanic eruption in Germany, and above it a separate Younger Dryas boundary layer rich in microspherules and platinum-group nanoparticles, about 150 years later. This matters because some researchers had proposed the Laacher See eruption as the trigger for the Younger Dryas. If the two layers are distinct, that particular eruption is ruled out as the cause. As Moore put it, “This demonstrates that the volcanic eruption and the Younger Dryas Boundary were separate events.” The authors favor an impact or airburst as the trigger, while acknowledging that another eruption at around the same time cannot be ruled out. The paper appeared in ScienceOpen Research.

The Case Against in 2026

A volcanic challenger. In April, a Texas A&M team published a study in Science Advances titled “Volcanic Forcing of Global Climate Cooling at the Younger Dryas Onset Preserved in North American Sediments.” Working with well-dated sediment records from Texas and Florida, they measured osmium isotopes and related elements. Their argument: the osmium signal that impact proponents cite as extraterrestrial can also be produced by volcanism, hydrothermal activity, or weathering of basalt, and their data fit volcanic aerosols better. They linked the signal to a period of significant volcanic activity, recorded in Antarctic and Greenland ice cores, between about 12,980 and 12,870 years ago. They also noted that no crater has ever been found, and that platinum spikes in some records slightly predate the Younger Dryas onset.

Two retractions. On February 11, 2026, PLOS One retracted two 2025 papers that had received wide media coverage as support for the impact hypothesis:

  1. The Baffin Bay paper, which reported cometary dust, microspherules, and a platinum anomaly in four marine sediment cores off Greenland. The retraction notice cited concerns about referencing, methodology, and data reporting. According to Retraction Watch, some particles identified as comet material were found to be foraminifera, the shells of tiny marine organisms. A coauthor acknowledged at least 43 incorrect references.
  2. The shocked quartz paper, which reported shocked quartz grains and other markers at three classic Clovis sites: Murray Springs in Arizona, Blackwater Draw in New Mexico, and Arlington Canyon in California. The editors cited problems with the age model, including that not all available radiocarbon samples were used, and noted that sediments above and below the key layer had not been analyzed, so it could not be shown that the markers were unique to the Younger Dryas boundary.

In both cases, several authors disagreed with the retraction. Moore described the problems as procedural and said they could have been handled through corrections. That is worth noting in fairness. But a retracted paper can no longer be cited as evidence, and these were two of the most publicized supporting studies of recent years.

They are not the first. In April 2025, Scientific Reports retracted a 2021 paper by researchers from the same network that attributed the destruction of the Bronze Age city of Tall el-Hammam, sometimes linked to the biblical Sodom, to a cosmic airburst. And a major 2023 review by Vance Holliday and colleagues argued that much of the proposed impact evidence can be explained by ordinary terrestrial processes.

The Scorecard

QuestionWhere it stands
Did abrupt cooling happen about 12,900 years ago?Yes. Undisputed.
Is there an unusual layer at the Younger Dryas boundary at many sites?Contested. Supporters report it widely; critics argue the markers are not unique to that layer, and two key papers were retracted over exactly this question.
Is the platinum and osmium signal extraterrestrial?Contested. The 2026 volcanic study offers a terrestrial explanation for the same signal.
Was Laacher See the trigger?Probably not. The Swedish core suggests it came about 150 years too early.
Is there a crater?No. Supporters argue an airburst would not leave one.
What does the scientific mainstream think?Skeptical. Meltwater remains the leading explanation, with volcanism a rising alternative.

Our Verdict

The impact hypothesis is not dead. The Greenland and Swedish studies are real data, published in 2026, and the Swedish result in particular removes one rival explanation. Some serious researchers continue to defend the idea.

But 2026 was a hard year for it. Two of its most widely reported recent papers were retracted, a third from the same research network was retracted the year before, and a credible volcanic explanation now competes for the same chemical evidence. It is also fair to note that much of the supporting work comes from a single network of collaborators, and that the two 2026 supporting studies appeared in newer, smaller journals than the volcanic study in Science Advances. None of that makes the supporting studies wrong. It does mean they need independent replication before they carry the weight their headlines suggest.

At Heterodox Prehistory we take catastrophism seriously. The geological record is full of sudden, violent events that the old gradualist model underestimated. That is exactly why we hold this hypothesis to the same standard as any other. Heterodox does not mean credulous. Right now, the honest score is this: an impact at the Younger Dryas onset remains possible, but the evidence for it is weaker at the end of 2026 than it looked at the start. We will keep watching, and we will update this scorecard when the evidence moves again.

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