I've seen elsewhere that if a terrestrial planet had a ring system, it would be very difficult (if not impossible) for life to evolve due to the shadow the rings would cast on the temperate zone in the winter time; it would be much, much colder.
Whether or not that is in fact the case, suppose there were some sort of...collision or other catastrophic event (such as a large asteroid getting too close and being torn apart in Earth's roche limit) that caused a ring system to form, even if only for a cosmically short period of time.
Would/could a ring system be created from such an event, and if not, are there any cases where it could happen?
If so, how long would it take the rings to form? How long would they last?