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# Physics/Percentage of water

Question
Hi,

What percentage of the Earth's surface does water cover?

- My Science teacher handed out notes to my class and that package says "75%"
- He also gave us an Assignment package and that one said "70%"

- When I filled out the Assignment sheet, there was a question that said "What percentage of the Earth's surface does water cover?", and so I wrote "70%". And he marked it as correct.

- So now I am confused because when I research this question, it gives me even more possible answers. I am still not sure whether I should write 70% or 75%? This type of question is most likely to be on my test tomorrow and I would like to know which answer I should write.

- Thanks

Hello Jason,

I would say that if your teacher wrote the test, you should write the answer that was in the teacher's notes. If the test was written by the source that said 70%, then that should be the answer you give.

Now I'll throw you a curve. I also did some research and got different answers. I'm more likely to believe some web sites than others. Here are links to 2 that I would put some faith in.
http://www.noaa.gov/ocean.html
Both of those say 71%. Notice that one says oceans cover 71% but doesn't mention how much freshwater covers. The other says fresh and saltwater cover 71%. But anyway it wouldn't be such a nice round number. When I was first taught about pi, I was told it was 3.14. Later I learned it was 3.1416, and then 3.14159. And then I heard about people memorizing pi out to 20 or more places. So I'm sure the percentage of water coverage is not exactly 71%.

I did see a couple websites that said 3/4 was water. But those were sites that I wouldn't put faith in.

I hope this helps,
Steve

Physics

Volunteer

#### Steve Johnson

##### Expertise

I would be delighted to help with questions up through the first year of college Physics. Particularly Electricity, Electronics and Newtonian Mechanics (motion, acceleration etc.). I decline questions on relativity and Atomic Physics. I also could discuss the Space Shuttle and space flight in general.

##### Experience

I have a BS in Physics and an MS in Electrical Engineering. I am retired now. My professional career was in Electrical Engineering with considerable time spent working with accelerometers, gyroscopes and flight dynamics (Physics related topics) while working on the Space Shuttle. I gave formal classroom lessons to technical co-workers periodically over a several year period.

Education/Credentials
BS Physics, North Dakota State University
MS Electrical Engineering, North Dakota State University