I'm no space science maker person. So take this all with a grain of salt. But. Halley's Comet takes 75 years to make an orbit. It goes out to about 35AU. Let's

I'm no space science maker person. So take this all with a grain of salt. But. Halley's Comet takes 75 years to make an orbit. It goes out to about 35AU. Let's call that 1 year per AU. That rough, rough number would lead one to conclude that anything from the Oort Cloud moving at a similar speed could take, say, 100,000 years to get here even if it was aimed at us. If triggered by something 70,000 years ago, we'd still have a bunch of millenia to prepare. Anyway. I'm sure I'm completely wrong.