What would happen if every person on Earth jumped into the ocean at the same time?
I assume you want to know how much the seas will rise as a result. Let's do the math.
- We first need to know how many people are jumping in the water. That's easy. There are around 7.6 billion people on Earth right now.
- Next we need a need to figure the average mass per person, so we know how much water will be displaced. We may quite a bit in size, but this is one of those questions for which a rough estimate will work. The average adult male is around 75 kg. The average adult woman is around 50 kg. Figure children at 25 kg. World population is roughly 1/3 adult males, 1/3 adult females, and 1/3 kids, so we can pretty safely use 50 kg as a rough estimate for the average human mass.
- Now that we have mass, we need average volume per person. Here, we get lucky. The average human is 985 kg/m^3. That's just a bit less dense than water. For our purposes, we can round up a bit and and use 1000 kg/m^3. Our 50 kg person has a volume of 50 liters.
- Now we need the volume of all of those people together. 7.6 billion people x 50 l per person is 380 billion liters. That works out to about .4 cubic kilometers if everyone is packed solid.
- Next comes figuring the total volume of the ocean. The consensus estimate is that the oceans contain 1.37 billion cubic kilometers.
Tossing an extra .4 cubic kilometers into something with a volume of 1.37 billion cubic kilometers would be less than noticeable. To put things into a more easily understood perspective, it would be like taking a raisin, cutting it in half, and tossing it into an Olympic-sized swimming pool.
So the great All-Human Dive might be fun, but it isn't having any kind of effect on the oceans.