could it be that planet 9s obit crosses the earths orbit every few million years in a way that it fucks with the earths gravitational field so that volcanoes explode and whole species like the dinosaurs get extinct?
No, but in the 80's they theorized a planet 9 type object was responsible for sending shit from the Oort cloud toward earth.
Whats more likely is there is a large object far out past Neptune that passes though the Oort cloud on a millions of year long orbit causing junk from the cloud to be thrown inwards which explains periodic mass extinction events and bombardments on Earth.
And volcanoes exploding didnt kill the dinosaurs you tool.
that hurts to read
Well there was the hypothesis that some object caused asteroids and comets from the Oort cloud to fall into the inner solar system every 26 MA or so, but planet 9, if it exists would never go that far in itself. That still wouldn't explain primarily volcanic events like the Deccan Traps being active at roughly the same time as the Chicxulub impact, or the Siberian traps in the end-Permian.