There is a theory out there concerning an impact in Argentina over 3M years ago that wiped out some South American species as being the last major impact, and most know about the big one North of the Yucatan that is attributed to the demise of the dinos, 65M years ago.
Likewise, really large volcano eruptions have been attributed to major losses of flora and fauna. A few came close to wiping out Homo sapiens if you can trust the work of certain researchers.
Evidence seems to support large impacts occurring over millions of years while major volcanic eruptions occur over thousands or hundreds of thousands of years. Take another look at the ice core data chart. As far as I know, the science behind its accuracy is pretty solid (please direct me to evidence otherwise).
Looking at only the last 400K years, it’s hard to miss the four unusual periods of VERY short term warming (relatively) before temperatures fall again. The odds are good that some sort of cyclical phenomenon is causing this warming. IMO, either the sun through increased output, or heat pulses from the earth’s interior (warming oceans) are the likely candidates. I don’t see how an impact would cause a warming period; much less not leave recent evidence behind, since we’re at the end of the current 12K year warm period.