The probability that humans prevent a future planetary mass-extinction event from celestial impact, divided by the probability that horseshoe crabs prevent such

The probability that humans prevent a future planetary mass-extinction event from celestial impact, divided by the probability that horseshoe crabs prevent such an event is so large that it might as well be infinity. Horseshoe crabs don't even have a theoretical plan. They don't even have a Hollywood blockbuster movie about it. So from a planetary ecosystem perspective, every species on Earth not directly involved with humans or horseshoe crabs should prefer to force the horseshoe crabs to help the humans in some way whenever they are able to do so. Those species should also prefer that humans not make horseshoe crabs extinct, just in case that they might be the critical link in some "for lack of a nail" causality chain which prevents humans from preventing the mass-extinction event. It's very much like forbidding a brilliant researcher from doing his or her own cooking and laundry. You hire a less-brilliant assistant to take care of all mundane needs, so that the researcher is thinking about your important problem at peak efficiency. Besides that, the guaranteed-to-work plan for dealing with a massive meteor strike is to transplant additional copies of Earth's ecosystems to other planets. If you build a Mars colony, and ship enough seeds and embryos there, you have prevented the extinction event, even if you couldn't do anything about the meteor impact.