I have a 1997 s320, with a few rockchips in the windshield.

Today i noticed a large crack extending from the top of the windshield through one of these rockchips, to about halway down my windshield. I was baffled and thought someone may have done this. Could this have devloped from heat?

If you feel over it you can't really tell it's there. What do i do from here? Do i have to replace the windshield? Can it be repaired? How much is a windshield for a w140? Any help is appreciated, thanks.