Underbody Shield problems of the 1999 Chevrolet S10

I had just noticed through my front wheel well that there was a crack in my frame. I took it to a mechanic and they had never seen anything like that before. He had noticed that it is cracked on both sides and my rearend is also affected by the cracks in the frame. The frame is not rusted and I have never been in an accident or have taken it off road. It has 127,000 miles on the truck and it is a 1999 so it is only 6 years old. There is no plausable explanation for this I would like an investigation done so this doesnt happen to anyone else. I will be taking it to the dealer I bought it from also to see what can be done.