How do we know these books are written by them? Where does info on Mark and Luke come from?
It really depends who you ask, nothing is actually certain, whether Mark/Luke wrote them or not. From Paul's letters we know Luke, a physician, was with him on the journeys where Acts has "we" passages (such as "we sailed to X city, and departed with Paul to X place", they start around Acts 20:1 and on - Colossians 4:14 - Caesarea).
As far as the information, that's the early Church tradition starting with the fragments of Papias written around 120, that Mark wrote his Gospel around 64 through Peter. Luke is also unanimous for the author of Luke-Acts. However, there were many early traditions that are clearly incorrect, such as Paul being born in Giscalis, Judea (Jerome,
Lives of Illustrious Men, 5), even though Acts clearly says he was born in Tarsus (Acts 9:11, 21:39, 22:3, 22:27-28).
I think if you wanted to see early traditions about Mark and Luke, and others (especially John) you should see the references in Irenaeus.
Also, how are we able to date the approximate writings of the gospels if we have no original copy to date?
Aside from the P52 fragment that means John was composed before 100 AD, the testimony of the early authors place the composition of the other Gospels in the 1st century as well. After that, it's entirely from internal evidence. Personally, I think Matthew, Mark, and Luke belong to 65-80, and John 80-100.
And is there an "original" copy? It seems like these would have to be passed around orally first if all the gospels were written that late (60-90 AD). If one was an eye witness, I don't see how they could remember all the detail on their own like this unless it was written much much earlier.
Yeah, the stories and sayings of Jesus were most definitely passed around orally for at least 30 years after Jesus' death, seeing how Paul in 1 Corinthians 10-11 (written c.55) refers to them instead of any Gospel. But if you see the traditions and compare the ones in Paul with those of the Gospels (such as, for example, 1 Thessalonians 4:16-17 with Matthew 24:30-31), you will see that even though they were passed around orally, they were kept very reliably.
I'm just curious. I was just reading my bible the other night and stuff and I was just wondering. Also, any advice on where to look on more info on this type of stuff? I'm very interested in the history of the different books of the bible and the people of the times.
For the date/authorship of the New Testament, I would suggest the Catholic Encyclopedia (newadvent.org), or you could visit my site, if you want to see some arguments about the authenticity of disputed New Testament writings: bible-apologetics.com/history/ephesians.htm - it has 7 out of 27 NT books, but I didn't do any of the 7 universally accepted Pauline letters: Romans, 1-2 Corinthians, 1 Thessalonians, Galatians, Philippians, Philemon, so that's about 14 out of 27 books :/