Until quite recently, research into comet and asteroid hazards was focused on establishing the scale and scope of past impacts, credible estimates of their recurrence, and models for physical impact scenarios. If there is still much to be done, the threat does seem convincingly demonstrated. CAI hazards have moved well beyond the realm of ungrounded speculation and apocalyptic visions. The results represent more than just new findings. They revolutionize, or are about to revolutionize, some basic understandings about the Earth, its history, biological evolution and future. Although human life has had a tiny place in the story so far, our longer term fate seems to be challenged by these forces and may be decided by them.