- last post: 01.01.0001 12:00 AM PDT
What I think is:
1.) Earth is likely not the ark itself, but likely related to it. Why? Too obvious, Bungie likes to play with the fan's minds. Of course, this could be paranoia.
2.) I believe Cortana is speaking of her own free will. Gravemind is ancient, and perhaps they played a little game of "I ask, you ask." Gravemind likely spread a wealth of knowledge to Cortana, and much like the occurences from First Strike, it is slowly corrupting her, not to mention her age.
3.) IT IS Master Chief. John 117 was the Spartan Cortana was obviously most acquainted with, seeing as the only Spartan's armor she had entered was John 117's.
It's impossible to speculate as to the Covie/Human alliances. This trailer provides nothing to support any theories, and Bungie wanted to avoid any main plot give-a-ways. They would not risk hiding something in the trailer, no matter how well hidden if it could give away major plot points.
There has to be more to that opening in the earth. Remember that crystal that warped gravity in First Strike? Bungie likely threw another mystical type object into the game. The only thing I do know is the Covenant should run. I think in that opening there lies something neither race would like to encounter.
Now remember, I am a retard, and extremely bored, and throwing in my two cents. Although I do think the Stargate theory would be pretty badass.