system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: What would it be like to be in the bottom of the Mariana Trench if the ocean was drained?

Would you be able to breathe easier than at sea level? Would it have an effect on your weight?
gpt
The air would be quite dense, about 4x that of sea level, and might result in a mild case of decompression sickness if an individual were returned to sea level without regular stops, but milder than an actual scuba dive.  Breathing would be very efficient, though.  It would be very cold, getting only a few hours of daylight depending on the orientation of the trench (I don't have any images handy).  Gravity would hardly change at all, with the 7 mile depth being only a tiny fraction of Earth's overall radius.