: (And compared to "we only use 10% of our brains", Halo is doing
: fine :P)

$5 says the compound is the Precursor powder that eventually led to the Flood outbreak that started the prehistoric Human-Flood War. $10 says that it came from the crashes ship on Installation 04 from the Halo CEA terminals that never communicated with 343 GS that he build a sarcophagus around. I think this segment was sent through a slipspace portal and found its way on the other end to the surface of Sedra. The impact of the segment of 04 hitting the surface of Sedra damaged/freed the sarcophagus from around the crashed ship and the white powder contained in the ship was freed onto the landscape of Sedra and/or Installation 04 where colonists found the wreckage.