Subject: Why gene structure differs in archaea, eubacteria and eukaryotes

In archaea and other lower organisms the genes are simply long linear structure
but in higher eukaryotes it has a split structure (e.g., introns and exons).
This difference seems "sudden" in terms of evolution and also the number of
genes vs genome size is very different in each group. Why? 

Re: Why gene structure differs in archaea, eubacteria and eukaryotes