The Marianas Trench is something like 37,000 feet deep, so removing all the water would make it the location of the highest air pressure on Earth.

I will see if I can figure this out . If you go up 18,000 feet you get to the elevation of the “ Half Pressure”

Go to 36,000 feet up , and it will be the 1/4 pressure. So a rough estimate would be 37,000 feet is the elevation of the 1/5 th pressure of the atmosphere.

So Now, let us go down.If we go down 18,000 feet it would be the double pressure . If we go down 36,000 feet it would be the Quadra- Pressure, ( 4 X) and at 37,000 feet you would be at the Penta- Pressure.(5 X )

At minus 37,000 feet the air pressure would be FIVE times the current air pressure at Sea Level.

And since PV = nr T, and the Pressure and the Volume of air above you would both go way up, then the temperature would go way up. Since the pressure is now 5 times that it is at sea level, and the Volume is 1 Plus 5 = 6 X. The PV would go from 1 X 1 = 1 to 5 X 6 = 30.

You would NEVER make it to the Bottom on a hike down. You would die from over heating way before you got to the bottom, even if you started in the Evening and hiked down at night.

For Comparison Vensus has a surface Pressure of around 93 times that of the Earth, its surface temperature is that of molten Lead at 737 Kelvin ( If I remember right ), and Earth may have creeped up to a mere 289 Kelvin. Water freezes at 273 K, and Boils at 373 K Delta T = 737 – 289 = + 448 K. for a change from 1 P to 93 P Delta = + 92. so + 448 / +92 = 4.8696 K / 1 P and 30 X 4.8696 = + 146 K.

So adding 146 K to 289 K = 435 Kelvin.

435 – 373 = This is 62 degree centigrade ABOVE the Boiling Point of water at sea level at an air pressure, and Volume of the Air column that is 30 times that of Sea Level Now. So 146 / 448 = 0.325 AND

30 / 92 = 0.326 ………………. 0.325 is very close to 0.326. And 146/448 is close to 30 / 92.

Any way, hiking down the bottom of the Marianas Trench would be a very grim way to die by boiling away in your own juices.