I think it's more like a grain of sand hitting a basketball.
Massive tidal waves ? Yes. End of life. ??????
The size of a bullet relative to a grown man is pretty small too, but it kills.
I don't think it's quite that simple. They believe the impact that contributed to the extinction of the dinosaurs was an object the size of Mount Everest. When it hit, the upper part of it was still in outer space, that's how big it was. An object that large hitting the Earth causes a chain reaction that would eventually leave us without good Sunlight for a long period of time, which would mean the death of most living things on the planet. We are talking about an explosion of over a billion Hiroshima bombs here, OVER A BILLION!! If one like that hit in the Gulf of Mexico where they believe the one I mentioned did, most of the water would 'slash out' of it, onto land in the form of a tsunami about as bad as we could imagine, and that's just from the immediate impact.
I read a few years ago that 90% of the observers were in the northern hemisphere. Presumably there is a 50% probabiliy that a major strike would hit the southern hemisphere. I hope Australia, South Africa, India, Indonesia, Brazil, Argentina and Chile get their butts in gear on this.
As for the danger. We are here because a major strike caused the end of the 150 million year dinosaur dominance. I think that about 70% of all genuses were killed off by that one. The one at the end of the Permian killed off over 90%. And this figures are only for the genuses, not for the far larger quantity of creatures.