One of the popular theories regarding the origin of Clover was that something (possibly a satellite) crashed into the Atlantic, awakening the monster.
You can see the item crashing into the water in Rob's video.
But the canon comic Cloverfield/Kishin revealed that the monster was awoken by submarines sent by the Tagruato corporation.
What fell into the ocean, and what was the significance of it?
As Vogie mentions in his comment, the movie's viral marketing campaign included an extensive mention of a falling satellite, the ChimpanzIII.
Tagruato used the Hatsui satellite to try to identify a rogue piece that is thought to have fallen off of the Japanese Government's "ChimpanzIII" satellite. Although Hatsui’s work has not yet been able to confirm the identity of the fallen piece, Tagruato scientists and engineers are busily trying to track and recover the fragment. According to Hatsui data, it disappeared into the Atlantic Ocean late last week.
It has since been confirmed in the Blu-ray special features that what woke the 'Clover' monster was a submarine sent to investigate the satellite crash rather than the crash itself.
