So what is an RNA world anyway?
Well, that's both more and less complicated a thing than you might think. First lets talk about your genetic material, the stuff that makes you who you are.
See, you DNA is the medium used to store your genetic code. It is the book upon which the story that is YOU has been written. Now, if you want to share portions of a book with your friends you don't rip out the pages, do you? I hope not... you either have them buy their own copy of the book (unfortunately human cloning isn't legal in the States) or you make a copy of the page(s) you want to share with them.
This copy of the page is akin to your RNA. Now the copy doesn't have all the information, and it is more likely to be broken down, degraded, or outright destroyed than the book with its heavy binding. Much like RNA is a more transitory molecule than DNA... it breaks down easier and is not as stable.
Well, DNA store the information in each of your cells and uses cellular machinery to make RNA copies of the instructions that need to be carried out.
Well that fact raised a lot of questions. See, RNA is ubiquitous to all forms of life. The DNA ~> RNA cycle is also ubiquitous to all forms of life (we are excluding viruses from this discussion for the time being). DNA acts ONLY as a storage device (in most cases) and RNA is the functional form of genetic material in a living creature.
Because RNA came first.
::ducks bits of rotten veg and cans being thrown at him by the conservative scientists and religious fanatics in the audience::
See, RNA was the most likely form of genetic material to have evolved initially: It is the simpler genetic molecule (DNA is actually a modified form of RNA) & it is the most diverse form of genetic material capable of storing and transferring genetic information, transporting amino-acids (as in the case of tRNA), structural activities, and even enzymatic activities.
When life first evolved, there were no molecules available to carry out these functions. Over time, other molecules evolved that can do the job more efficiently or more effectively, but none of them are capable of doing ALL of them, except RNA. It was the evolution of RNA that allowed for the first truly LIVING organisms to exist, evolve, and develop more advanced forms of structure and catalytic activity (in the form of proteins) and safer genetic storage techniques (DNA) furthering the evolution of RNA and organisms extensively.
Now for many of you, this is a moot point. Whether RNA or DNA came first is of little importance... or perhaps you don't even believe in it at all. And, I guess, that is your right. If you want to believe that the sun does not shine or that water is not wet, then who am I to tell you any differently.
But there are those who take matters such as this far more seriously than you or I... the same type of people that try to ban evolution in our schools, animal testing in our laboratories... the type of people willing to commit acts of violence against organizations, and people, who try to advance these types of studies.
But, no worries. I'm only a student after all... who'd want to come after me.