The War Of The Worlds by H.G. Wells (forget the films. The Jeff Wayne record did give it some justice)
There is some science in the book and this coincides with the proposal/argument from astronomers at the time (serialised in 1897 and first published as a book an 1898) that intelligent life existed on Mars. At the beginning there is some geological and evolutionary proposals mentioned as a kind of background explanation and further into the book a delve into Martian biology and speculation on the mechanics of their weaponry but as far as I can recall that's it on the 'sciency' front so it may not suit die hard Sci-Fi fans, but it is probably one of, if not the first book of it's kind.
The reason I recommend this book is because of the thoroughness with which it is written. Wells' ability to describe situations and emotions with such accuracy and at the same time also poetic beauty puts him up there, in my humble opinion, among the best authors ever. I have read the book a dozen times and although it isn't particularly long, there is always something new. I felt as though I was walking in the author's shoes and I could smell the electricity in the air in the chapter 'in The Storm' and the terrifying images revealed with each lightning flash through the darkness.
The book was written in the style of a journal, the authors first person character being a journalist and this is probably one of the the reasons it comes across with such authenticity.
Anyway, enjoy your search for Science Fiction books.