Do extinction events such as the Cretaceous-Tertiary Mass Extinction event prove the Great Chain of Being wrong? indeed I would assume so.
Can someone explain this in detail because I have been informed my whole life that the great chain of being is true.

Assuming your referring to the Christian "Great Chain of Being" then no.

Explanation:

(I will try to be as unbiased as possible)

Just to clarify for anyone who is uniformed on what exactly the Great Chain of Being is... it is a hierarchy chart which first surfaced in Medieval Europe which goes in order as... God, Angelic Beings, Humanity, Animals, Plants, Minerals.

In the Bible it is stated numerous times (I can find the specific page and such if needed) that "great beasts" roamed the earth... now there is no historical or scientific evidence this was referring directly to Dinosaurs but there is evidence that mass extinction events have occurred all throughout history and some are event mentioned in the bible itself (The Great Flood) It is thought that about 75% of all animal life on earth was wiped out (Also most believe that some form of Humanity was alive during the supposed asteroid strike) which means that if you are arguing that a mass extinction event would mean that Great Chain of Being or basically the existence of God then you would be wrong. (Again being unbiased here, there is also no evidence that there is a "God" or Gods)

I hope this could help, my apologies if it didn't. If you need any more elaboration I will gladly try my best to help out down in the comments