The Younger Dryas Impact hypothesis is one of the more interesting topics I've been following recently. The summary of events is as follows:
Overview
About 12,800 years ago, a giant broken-up comet
- caused airbursts or craters across Northern Hemisphere
- deposited melted material in the Younger Dryas boundary (YDB) layer
- melted parts of huge northern ice sheets covering Canada and Europe
- halted circulation of massive amounts of ocean water in North Atlantic
- triggered 1,100-year-long climatic cooling, called the Younger Dryas
- contributed to the extinction of millions of large animals (megafauna)
- caused a major decline in human population levels of approx. 50%
Evidence:
Millions of tons of material, melted at high temperatures,
- is at more than 36 known sites
- is at every site currently investigated
- is spread across 16 countries on 4 continents
- ranges from offshore California to the Middle East
- has no geographical limit to the extent of distribution
- covers 20-25% of the N. Hemisphere (map on next slide)
- dates to approximately 12,800 years ago at the start of YD cooling
Source: https://cometresearchgroup.org/
All published peer-reviewed research: https://cometresearchgroup.org/publications/
If you find this topic interesting, I recommend watching this Joe Rogan video where he interviews Randall Carlson and Graham Hancock about the evidence for the event.