The BT chemicals in the polymers of the UV radiation and asbestos
In will most likely decrease its speed.
hope this helps.
Technological advances clearly.
Theories change due to other peoples view on the matter and how they experiment with it, but Technology advancements are the greatest factor of all. I mean seriously, we wouldn't know of cells before the microscope and when they first invented it, it advanced further and now we can see things on a whole deeper lever.