So could we survive a direct meteor hit?

Reading this thread got me thinking. If the earth were hit by a large meteor, would we, as a race, survive? Obviously we’d have a large percentage of fatalities, but do we have the technology available to survive (long-term) severe climatic changes, or anything else that might happen?

To paraphrase Bill Clinton, “It depends on the meaning of the word large”.

If it’s the size of the moon - No.

It all depends on your definition of large.

A one kilometer asteroid would disrupt a lot of systems, cause huge changes, and some humans would probable be able to survive, even without leaving the surface of the planet for any extended time.

A ten kilometer asteroid and the number of humans drops pretty rapidly, but it still makes some sense to believe in a continuation of the species. Probably not under any recognizable social system currently in existence.

A hundred kilometer asteroid and the species surviving are unlikely to include anything over ten pounds, and not much of that. Permian disaster period fossils don’t leave you with much confidence. Eighty percent of everything dies. What is left is those things that are most able to survive without specific prey, or symbionts. That doesn’t include humans unless they dig deep, and stay down a long time.

A thousand kilometer object and you have a clean slate. A few single celled species able to survive, and a new ecology develops over a half billion years or so. Humans leave no traces. (OK, the so-called Plutonium Layer is hotly debated as proof of ancient civilizations, but no real scientists take it seriously. The remains of the Apollo project would have been proof, but of course that was just a hoax.)

The sizes are approximate, of course. It might take a two-kilometer object in the first case, or a seven hundred-kilometer object in the last. The chances are astronomically small, which is to say, inevitable, over astronomic time periods.