Fan blade on Dart broke today

All right, I got down to the shop today. There is a very small nick on the underside of the hood. The belt itself has no marks on it anywhere. It did not hit the fan. All the bolts, including the ones holding the rest of the blade where half the hole was broken off, were tight. One of the blades of the fan part still attached to the car was bent a bit and had a slight crack. I have no idea what happened. I am inclined to go with age and stress, as has been mentioned by toolmanmike.

View attachment Fan blade.jpg
View attachment Fan blade broken.jpg

This is the bent and cracked blade.

View attachment Fan blade cracked and bent.jpg