The Bible was written by about 40 different people, over probably a 1000 year time. Each of those 40 people were inspired by God's spirit as they wrote.
The book of Job is considered the oldest book. Job was even before Moses. The first 5 books, starting at Genesis, are called "Torah" by Jewish folks. They were written by Moses, and are the "Mosaic Law" upon which all the modern Jewish laws were based (although God said no laws should be added...)
The original Hebrew version of the Torah has some amazing properties, and if you choose to research it, you'll be convinced that it is supernatural. I just found http://www.britam.org/codesarticles/CodesIntro.htm... which has some interesting info.
The New Testament was written after Jesus died, rose, and returned to Heaven. When the New Testament says "law" it means the Torah. The Old Testament did exist at the time of Jesus. Jesus himself read from Jeremiah and mentioned Daniel and other prophets, all in the Old Testament.
The best really old copies of biblical text were found in the 1940's in a cave, and they are called the Dead Sea Scrolls.
The most important thing about having old copies, and many different copies, is that smart folks can compare all of them to each other, and look for differences, to prove whether or not our Bible is accurate.
The bottom line is that we can trust our Bible, because there are no differences in old copies that actually change the meaning we have today. I think the percent of differences is very small, like less than 10%, which is pretty amazing since it was copied by hand so many times starting over 2000 years ago.
If you can, I recommend checking out 2 books, called "Evidence That Demands a Verdict" and "The Case for Christ". They explore the history of the Bible and many other great topics.