Around 12,900 years ago, the world was warming fast. Then it suddenly plunged back into cold for about 1,200 years. Some researchers think a comet impact triggered it. Many others disagree.
Truth label: Debated. Serious people disagree. You get both sides.
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The case for an impact
Supporters point to a layer of sediment at many sites with tiny spheres, platinum spikes and soot, which they say came from a cosmic event.
The case against
Critics say these markers are not found consistently, and that melting ice sheets changing ocean currents explain the cold snap well enough.
Why it matters
If true, a catastrophe hit just as people were on the edge of farming. It is at the heart of many "lost civilisation" theories.
Learn
- What everyone agrees on. The sudden cold snap, called the Younger Dryas, really happened. The question is what caused it.
- The two main explanations. A cosmic impact, or a flood of meltwater shutting down the Atlantic currents that keep the north warm.
- What would settle it. A crater of the right age, or impact markers found consistently at the same moment worldwide.
Test yourself
Which part of this story is established?
A sudden cold snap happened. The cold snap is well documented. Its cause is what is debated.
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