Maybe the Earth-based technological civilization attracted the attention of a space-faring civilization, who dropped an asteroid to wipe out the Earth civilization (successfully, as it turns out).

Which means maybe we should be a bit more careful about bleating our existence out into the universe these days...

People who had this thought have also liked "The Dark Forest" and "Death's End" by Liu Cixin :) (These are part 2 and 3 in the "Three Body Problem" series.)

Also 'The Forge of God' [0] by Greg Bear [1987]:

"We've been sitting in our tree chirping like foolish birds for over a century now, wondering why no other birds answered. The galactic skies are full of hawks, that's why. Planetisms that don't know enough to keep quiet, get eaten".

[0] https://en.wikipedia.org/wiki/The_Forge_of_God

And in the 1970s by Gregory Benford, In the Ocean of Night.

And Footfall by Niven and Pournelle. And the Galacti Milieu series by Julian May.

Yes, it makes you realize this pop song from the seventies is not only incredibly cheesy but could be catastrophically dangerous

https://www.youtube.com/watch?v=_BrSVOOK610

As far as geo-engineering goes, I think what they'd be wanting to do is cause a super-volcano or three. You really don't want to be pulling asteroids down - just a couple of finely place nukes will do. Get a volcano going, put a few tons of sulphur in the air and you have a nice cooling effect. Just be careful of the unintended tsunami. Should probably just evacuate Iceland and keep popping the volcanoes until it's cool again.

Is there any theory that suposes this might happened, on a small scale, and the temps (and crust) warm? Could that loosen things up, so to speak, and trigger more volcanic activity?

Perhaps the asteroid was just an asteroid mining operation gone horribly wrong, or some form of planet killing warfare?

How about:

- bacteria with engineered enzymes for recycling (https://news.ycombinator.com/item?id=16856246) mutate/go wild and wipe out most/all traces of civilization

- what we can find today is just slightly elevated levels of whatever these bacteria mostly ignored.

This reminds me of the movie Snowpiercer

If you write it, I'll buy it.