How Do You Calculate the Mass of All the Water on Earth?

[Brewer]

If I've been given the density of water, how do I go about calculating the mass of all the water on Earth.

Of course, density = m/v, and whilst water covers 2/3 (?) of the Earths surface, how can I work this into the volume? Would it be the 2/3 * surface area of Earth * average depth of the oceans?

This is assuming that sea water has the same density as fresh water (which is obviously not the case, but still - its what the question states)

 

[vsage]

That equation is a good approximation if the surface area of the Earth around the depth you are told is comparable to the surface area of the surface of the earth. I'm a little unsure what you're actually given in the question and what you're not, though.

 

[kyle8921]

To calculate the mass of all the water on Earth, you would need to use the formula: mass = density x volume. In this case, the density of water is given, so you would need to calculate the volume of all the water on Earth.

As mentioned, water covers approximately 2/3 of the Earth's surface. To calculate the volume of water, you would need to multiply this fraction by the total surface area of the Earth. This would give you the total volume of water on the Earth's surface.

However, this calculation would only give you the volume of water on the surface. To get a more accurate estimate of the total volume of water on Earth, you would also need to take into account the average depth of the oceans. This can be estimated by taking the average depth of the five major oceans on Earth (Atlantic, Pacific, Indian, Southern, and Arctic) and multiplying it by the surface area of each ocean.

Once you have the total volume of water, you can then multiply it by the density of water to get the mass of all the water on Earth.

It is important to note that this calculation assumes that all the water on Earth has the same density, which is not the case. As you mentioned, seawater has a higher density than freshwater. To get a more accurate calculation, you would need to take into account the different densities of water in different parts of the Earth.

In summary, to calculate the mass of all the water on Earth, you would need to use the formula: mass = density x volume. The volume can be estimated by taking into account the surface area of the Earth and the average depth of the oceans. However, this calculation is an approximation and the actual mass may vary due to the varying densities of water on Earth.