It’s several.

One of the key details that seems to be ignored — much like several other modern concepts of cognitive dissonance, denial, dismissiveness, etc — is that even from the evidence we have collected thus far that we can readily review now, there wasn’t a single impact event marking the end of the Younger Dryas timeframe.

Was there an impact? Information does indeed seem to indicate there was.

Not one impact.

If you examine the GISP2 ice core data, yes, it most clearly indicates a sharp increase in temperature. But consider that data and the trends within a larger context.

Recall that it does point to a time period of cooling that was referred to as “the little ice age”. It’s recent — within the last 700 years or so.

Now look back a bit further.

Here’s the Younger Dryas period:

Now let’s look at the older time frame. In particular, consider the sharp changes in temperature.

There are, quite clearly, several sharp changes. The “Little Ice Age” was identifiable by a very small change that was very close to the current global temperature. But if you consider that the captured data quite clearly indicates extreme, sharp changes. Ignore the typical fluctuations. Look at the exceptional values — I’ve circled them to help identify them.

Those are significant changes between 16,000 and the acknowledged impact at the end of the YD period 11,500 years ago.

Don’t look for the one crater at the end of the YD. You won’t find “the smoking gun”.

Look for several.