There were four basic materials that the Egyptians used to build the pyramids: limestone, pink granite, basalt, and alabaster. Each type of material had a diverse use. Limestone had, for the most part, two uses.
To answer your question: The useful lifespan of a CPU is about 3-4 years. My guess on the technical lifespan under full load is closer to 8-10 years if nothing else breaks and takes the CPU with it. The reasons: High Performance Computing Clusters usually keep the computers for 3-4 years.
Laptops are subject to more abuse than desktops, which is why laptops have shorter lifespans. If the average laptop made today were placed in a clean, well ventilated room, it could likely run for 10 years without problem if no one touched it. A desktop would probably last 15 years without problem in the same condition.