Let's be clear about evaluating historical sources. Here's one list I found on the interwebs. There are others, but they mostly seem quite similar:
1. Was the source created at the same time of the event it describes? If not, who made the record, when, and why?
2. Who furnished the information? Was the informant in a position to give correct facts? Was the informant a participant in the original event? Was the informant using secondhand information? Would the informant have benefited from giving incorrect or incomplete answers?
3. Is the information in the record such as names, dates, places, events, and relationships logical? Does it make sense in the context of time, place, and the people being researched?
4. Does more than one reliable source give the same information?
5. What other evidence supports the information in the source?
6. Does the source contain discrepancies? Were these errors of the creator of the document or the informant?
7. Have you found any reliable evidence that contradicts or conflicts with what you already know?
8. Is the source an original or a copy? If it’s a copy, can you get a version closer to the original?
9. Does the document have characteristics that may affect is readability? Consider smears, tears, missing words, faded ink, hard-to-read handwriting, too dark microfilm, and bad reproduction.
So let's apply these to Mark's gospel
1. GMark is not contemporary. We don't know who wrote it and it was probably written three or four decades later and it was written as a theological document.
2. We don't know who wrote Mark and we don't know who gave him the information so we can't really answer any of these questions, except that they were probably using at least second hand information.
3. Mark has no dates. It does mention some people and places known to exist but it does make errors of fact in geography.
4. We don't know of any reliable sources concerning the life of Jesus, except maybe Paul and he is silent on almost every aspect of Jesus' life, plus Mark may be partly dependent on Paul.
5. Other than the other gospels which are almost certainly not independent sources, I know of no other evidence concerning the life of Jesus.
6. Yes. We don't know where they originated.
7. There's good evidence that miracles don't happen.
8. We do not have the original. This is true of all ancient documents but that doesn't mean we can discount the point, it means that it is a problem for all ancient documents.
9. Not applicable because we don't have the original.
Mark strikes out on every single criterion.
Since this was posted on the best bits thread...
I came across
this comment while looking into the contradiction between Mt 28:8 and Mark 16:8:
"On Mark and Matthew not experiencing the resurrection events directly: I believe that there is evidence that Mark did experience these events.
Generally it is understood that Mark is the same John Mark mentioned in Acts 12:12, who went on Paul and Barnabas’s first missionary journey Acts 12:25 (The Coptic Church holds to this understanding)
Additionally Mark 14:51 makes mention of a young man. Many believe this young man is Mark the Gospel writer as it was a vehicle of writing for the author of a writing not mention themselves by name but by a reference that others would know. We see this in John 21:20 where John references himself as the disciple whom Jesus loved."
Matthew's equivalent would be "Matthew the tax collector" in Mt 10:3. Luke is called "the beloved physician" by Paul. Perhaps Mark was a teenager when he was with them in Gethsemane.