have we ever been to the bottom of the marianas trench
Mariana Trench Four descents have been achieved. The first was the manned descent by Swiss-designed, Italian-built, United States Navy-owned bathyscaphe Trieste which reached the bottom at 1:06 pm on 23 January 1960, with Don Walsh and Jacques Piccard on board.[12][21] Iron shot was used for ballast, with gasoline for buoyancy.[12] The onboard systems indicated a depth of 11,521 m (37,799 ft), but this was later revised to 10,916 m (35,814 ft).[22] The depth was estimated from a conversion of pressure measured and calculations based on the water density from sea surface to seabed.[21]
Mariana Trench At the bottom of the trench the water column above exerts a pressure of 1,086 bars (15,750 psi), more than 1,000 times the standard atmospheric pressure at sea level. At this pressure, the density of water is increased by 4.96%, so that 95 litres of water under the pressure of the Challenger Deep would contain the same mass as 100 litres at the surface. The temperature at the top is 1 to 4 °C (34 to 39 °F).[5]