"Last happened 65M years ago" is very different from "happens every 65M years", though. It only takes one impact to ruin your whole biosphere. It doesn't have

"Last happened 65M years ago" is very different from "happens every 65M years", though. It only takes one impact to ruin your whole biosphere. It doesn't have to be a single cause, either. Some mass extinctions in our history are believed to have multiple causes, or be comprised of multiple smaller events. It must suck to live on earth in those periods, even before the overall event is complete. It's like how you want your wealth to be diversified in a sinking economy even before "A Recession!" is officially declared.