Reddit reviews What Is Scientology?

IIRC there is a timeline, including when the OT levels were introduced, in the back of the book What is Scientology?.

Also I think some of his ideas may predate Dianetics but all of the Scientology books came after Dianetics, most were written between 1952-1956 I think. From what I remember a lot of the OT stuff, though, was done in the late 60's and early 70's.

There are some books (and some books that are really pamphlets, I've seen it with my own eyes) that serve no true use to society, except to perpetuate fleeting fads. I'd be fine with their extinction--their survival is hardly necessary, especially when compared to the Great Gatsby and Lord of the Rings and even Redwall and Harry Potter, really.

The bible also has a huge pool already in existence, so unless each and every one of them burst into flames simultaneously, I doubt they'll ever really be extinct. You could probably still piece it back together from all the references it has had in literature, too--every single verse. Destroying even half the bibles out there would still leave a sizable amount in existence, not counting digital copies. When a book has such a pervasive presence, there is little harm in marking up the pages of just one book of just one edition.

https://www.amazon.com/What-Scientology-L-Ron-Hubbard/dp/1573181226

Both stores I visited had 15-35 copies of this book in paperback in virtually identical condition.

If you are near a good library try to find one of the big picture books with the word balloons. They are awesome and must have cost a fortune to print. Avoid Dianetics and anything written by an ex-Scientologist or anyone who doesn't know anything about it except what they learned on South Park.
The "religion" is certainly crazy but probably less so than most others.
This one will give you the basics:
http://www.amazon.com/What-Scientology-L-Ron-Hubbard/dp/1573181226