Want to make sure you back something up indefinitely? Then you could do worse than a digital data storage technique that uses laser light to store 360 terabytes of information on nanostructured quartz for up to 14 billion years.
Triboluminescence is light emitted by the mechanical stimulation of crystals. The first people to use it might have been a Native American tribe. Learn about the physics of glowing crystals and the people who used it.
A single volcanic eruption wiping out life on entire continents isn't exactly a cheery thought, but at least we had the mild comfort that it would take as much as 200,000 years for one to erupt. Yeah, about that...