How much water is tied up in *humans* on Earth? Things you might need to know to calculate this:
- population of Earth
- % composition of water in the average human
- average weight of the average human on Earth
- give your answer in US gallons. I know that science deals with SI units but not today.

When does a spring tide occur? question 9 options: they occur when the sun, moon, and earth are aligned. in spite of their name, these tides occur twice a year in the spring and fall. they occur on the date of the vernal equinox each year, no matter what stage the moon is in. this is why they are called spring tides. they occur when the sun, moon, and earth are at 45-degree angles from each other. this happens once every spring. they occur when the sun, moon, and earth are aligned. in spite of their name, these tides occur all year long.