Extinction is a normal part of the evolution of life on our planet. You and I and all individual organisms eventually die. That is the way of things. Entropy happens. Entropy is a word from the third law of thermodynamics that basically means: things fall apart. The natural tendency is for things to become less orderly as time goes on: things break down, things erode, things rust, things wear out. Entropy is a measurement of how fast that is happening in any given system. Individual death is a natural outcome of entropy. But an extinction is where all the members of a species are no longer living. Millions of species have gone extinct over the lifetime of our planet. There are natural background extinctions that happen continually. But sometimes there are events that trigger mass extinctions, where vast masses of species go extinct all at once (all at once in geologic terms, which might mean over the course of hundreds of years). There have been 5 mass extinctions over ...