Many translations include a note that the most reliable, earliest manuscripts of Mark do not contain verses 9-20. What's stunning to me is that they DO contain verses 1-8. The earliest Gospel ends with the Empty Tomb. That's a real problem for skeptics.
Some skeptics claim that the resurrection story was borrowed from Mithraism, a secretive Roman "mystery cult" that featured a resurrected god-man. Mark was the first canonical gospel written. It was compiled about 50 years after Jesus' death, most likely from eyewitness recollections (Mk 14:51) and a couple of now-lost written collections of Jesus' words and deeds. Fifty years is a long time. winesses die, memories fade, stories can shift with retellings. But Paul's writings show that belief in the Resurrection as a literal, historical event was prevalent just 20 years after the event. And 20 years is not enough time for "legendary accretion" to override living memory.
Other skeptics argue that the Gospels are simply fiction. But as a work of fiction in that culture, Mark really messed up by making the witnesses women. At that time, women were not allowed to testify in court because they were considered unreliable. Besides, there's no description of the moment of resurrection itself. I mean, come on! That's the climax of the story! If you're making it up, you really should have someone there to describe it, right?
You can set aside the doctrines of inspiration and inerrancy and look at the Gospel of Mark simply as an historical document. And even from that secular point of view, you're left staring into an empty tomb. Mark says that Mary, Mary, and Salome were trembling, bewildered, and afraid. Can't say as I blame them.
If I didn't know why the tomb was empty, I'd be pretty upset, too.