[Q: ok, assuming that the earth and the moon are close to the same age, 6,000 years or so. why are there so many huge craters on the moon, yet only one documented witness? gervaise of canterbury beheld such an event about 500 years ago when he witnessed a meteor hit the moon in a fiery explosion. he documented it. however, there are thousands of such craters, yet only one witness.

the big bang theory says that the earth is 4.5 billion years old, and during its youth, say the first 1.5 billion years, there were many such occurrences, which would explain the multitude of craters. however, in the past 2 or so billion years, this happens less frequently.

given this scenario, what would be the reasonable conclusion?]

"Well, for one thing, the Earth is NOT "millions of years" old. In a way, you may be right, that there were many such occurrences in its youth, but not in recent history. But it would only be a few thousand years old, not millions.
It's possible that the event (meteor?) that caused the collapse of the 7th layer of water or ice above the Earth (thus causing the Flood) may also have been responsible for the cratering of the Moon. The inverse square law says that when the distance between two objects is halved, the gravitational force is quadrupled. It would have shattered in mid-flight like a snowball, with parts of it hitting the moon.
This would also explain why there would be no witnesses - all but 8 of them would be dead, and the survivors were shut into a boat during that time."