Other mistake: When the water tentacle enters the rig, in one shot in the 4:3 version of the film on video you can see that the tentacle is a superimposed special effect because of the dead straight line where it is supposed to have come out of the water.
Continuity mistake: When Jammer is alone in the derelict sub and the alien appears, all the electrical devices shut down, as they do in the whole movie. But in the close up shots from the side of Jammer, you can see the light at the top of his helmet is still on.
Character mistake: When they're reviving Lindsey, Bud screams "fight" and slaps her. watch as she closes her eyes on the second slap while she is supposed to be dead.
Continuity mistake: In the under sea duel in the mini subs Coffee smashes the tape player with his elbow, in the next scene, as seen from the outside looking into his sub, you can see it's still intact.
Audio problem: When the crew are running around the passages, a guy with a beard yells something at Bud, and then uses a fire hydrant to put out a small fire. Funny, it doesn't make a noise.
Continuity mistake: When the SEALS take over, they lock up the crew. After closing the door on Ed Harris and the shouting Mary Elizabeth Mastrantonio, one of the SEALS hangs a hat over the spyhole. The next time we see the door, the spyhole isn't covered.
Revealing mistake: When the crane falls down in front of the rig and then over the cliff into the abyss it's as if the rig was already just a few yards away from the abyss but when the umbilical pulls the rig again (after Bud says to grab onto something) suddenly there's enough space for the rig to be dragged at least a few hundred yards as if the rig never moved from its touchdown position earlier in the film.
Revealing mistake: Every time the aliens appear anything electrical shuts down but somehow Lindsay's camera is able to take pictures of the small NTI before the electricity powers back on.
Revealing mistake: When Bud is unscrewing the trigger from the nuke down at the bottom of the abyss, there are no threads on the mechanism to require unscrewing. The part of the device that would have the threads is plainly visible.
Plot hole: Water pressure seems to be very picky in this film. It crushes Little Geek after passing 17,000 feet but somehow manages to leave Big Geek intact. Also if Big Geek could fall that amount of distance before imploding then why did Flatbed implode after only falling a few feet?
Factual error: When disarming the nuke Bud is trying to figure out which one of the two wires to cut. With only two wires running between two separated modules (in the film, one part is unscrewed from the other) any current flowing through one wire must be returned through the other in order to conserved electric charge. Cutting either wire, in this case, will result in breaking the circuit. There is no way for either side of the circuit to detect which wire(s) were cut.
Factual error: When Bud is dropped onto the spacecraft floor by the alien who rescued him, air trapped in his suit comes off in large bubbles. At 18,000 feet bubbles would be compressed so far that they would be BB size. Also, with all the movement Bud experienced on the way down, no air could possibly have remained trapped in the folds of his suit.
Continuity mistake: When Lindsay turns to see the UFO, she has cables running around her, but in the next shot, no cables.
Plot hole: Why wasn't the umbilical to the "Explorer" unhooked from the rig after the rig was set down? Everyone knew things were going to get rough with the hurricane coming, so the umbilical should have been taken care of before the hurricane became a factor.
Character mistake: When Bud is doing mouth-to-mouth on Lindsay, he's not pinching her nose closed, so all the air he's breathing in is going straight out her nose.
Plot hole: Coffey uses the submersible "Big Geek" to carry the armed nuclear bomb to the NTIs. If Coffey was that desperate to blow up the aliens, he could have much more easily set the timer for 30 minutes, driven one of the submersibles far out over the abyss past the drop-off, and simply dropped the bomb down and let it sink under it's own weight.
Visible crew/equipment: The ship is moving underwater and explosions are going off left and right. The main female character says she is going to check the battery room. As she goes, the camera is in front of her, and its shadow, including a microphone antenna are on her.
Continuity mistake: When the crane breaks off and falls into the water, it JUST misses the rig by a few feet (very visible when they're looking out of the window). Then the crane falls off of the edge and starts to pull the rig. The rig is pulled much farther than the previously shown distance to the edge.
Factual error: During the flooding of the drill rig, Bud's wedding ring saves the day by preventing the barrier door from closing. Even titanium couldn't stop a moving hydraulic barrier, in ring form. It's very hard in terms of resisting scratches, but that doesn't mean it wouldn't deform or crack.
Answer: Most of it was television news coverage about the increasing tensions between the US and USSR as it was playing out earlier in the movie. Additional archival footage from previous years' wars implied that the NTIs had been on Earth for quite a long time.