Most Optical Media degrades almost immediately, depending on storage environment, lasting as little as two two years before they start to degrade/aren't readable (depending on the dye and substrate). The MDISC is archival format - designed to last a minimum of 100 years when stored under reasonable conditions, and up to 1000 years if stored in archival (cool, dark) environments.

They are essential carving physical holes into a stone like substrate.

The verification tests are really quite impressive: http://www.esystor.com/images/China_Lake_Full_Report.pdf