Estimate the mass of water on planet earth. What fraction of the total earth mass is water?

Answer 1

I know the fractional weight of water is tiny, much less than 1%. Even by volume it's less than 1%.

Answer 2

Surface area of Earth is found by using the formula:

S = 4 π r²

where r = 4,000 miles

Oceans make up about 75% of the surface area, and have an average depth of not more than 2 miles. So, we have for the volume of the oceans:

V = (2) (3/4) (4) (3.14) (4,000) (4,000) cubic miles, or roughly 300,000,000 cubic miles.

Earth itself has a volume found by the formula:

V = (4/3) π r³ , or

V = (4/3) (3.14) (4,000)(4,000)(4,000) cubic miles, or roughly
81,500,000,000 cubic miles

The average density of water is about 66 pounds per cubic foot, while the average density of the earth's mantle and core is is approximately 500 pounds per cubic foot, so we have:

Weight of water = 300,000,000 (66) (5,280³) pounds
Weight of earth = 81,500,000,000 (500) (5,280³ ) pounds

so, the percentage of weight of Earth being water is:

(100%) (300 (66) / 81,500 (500))= 0.049%

Looking up facts, Earth is about 6 x 10^24 kg, and Oceans 1.4 x 10^21. So, the percentage is:

(100%) (1.4 x 10^21) / (6 x 10^24) = 0.023% of the earth's mass, so apparently the density of the Earth's mantle is closer to 1,000 pounds per cubic foot.

Answer 3

http://en.wikipedia.org/wiki/Earth
The Earth's hydrosphere consists chiefly of the oceans, but technically includes all water surfaces in the world, including inland seas, lakes, rivers, and underground waters. The average depth of the oceans is 3,794 m (12,447 ft), more than five times the average height of the continents. The mass of the oceans is approximately 1.35 × 10^18 tonnes, or about 1/4400 of the total mass of the Earth.

1/4400 = 0.000227273

Answer 4

I came up with about 6E-5 based on an earth mass of 5.98E24 kg and an average depth of 1km covering 70% of the surface area on a radius of 6376 km.