possibly the biggest gaff ever in film for a scientific expedition LOL.
I think two of the biggest gaffs I've ever seen in sci-fi films were:
1) in Deep Blue Sea, they talk about how the shark measures 6 feet across, but somehow it gets into a room they're in through a 3 foot wide door.
2) in Reign of Fire, there is only one male dragon for the whole colony/species. While there is precedent for this in many different animal populations, especially fish (clownfish, parrotfish, etc.), ALL those species that live in colonies like this have a way for a new lead male (parrotfish) or female (clownfish) to arise if the current one dies. This one really bugs me to this day.