What percentage of the Earth is water? What percentage of the Earth is land?

My students were quick to answer that the Earth is about 70% water and 30% land. Great answer, how do you know that information? The students responded with various sources such as it was it the science book last year, a previous teacher told me and my personal favorite - Google. You can ask Google anything.

So I asked how does Google know what percentage of the Earth is water and what percentage of the Earth is land?

Silence. And in typical middle school fashion, the students who had confidently answered the question with a fact a few minutes ago are no longer making eye contact with me. I love this moment. The moment when I know that I have created a learning opportunity. The moment when the question cannot be answered easily through a quick fact check.

I wait a little longer. Some students squirm a bit. Then a brave soul raises his hand and ventures a guess. A good guess. He suggests that since we have been to space, we could look at the Earth and estimate the percent of water and land. I like this idea. I share an image of the Earth from space and wonder aloud if estimating might be a challenge - you know with all the clouds. We brainstorm some other ways this information can be gathered.

**Working as Scientists**

I am ready for this moment. I have found an activity that provide the tools students need to learn how we know the ratio of land and water on our planet.

Surf n' Sand Count

I like this activity from AIMS - Activities Integrating Math and Science. Students examine a gridded map of the world where they estimate the land or water in each section and discover the ratio of land and water on our planet. This is a great $2.00 investment for a digital copy of the lesson. Click Surf n' Sand Count to see a lesson preview on the AIMS website.

**Sharing Our Results**

Google Docs

After completing the Surf n' Sand Count, we realized that not all students have the same ratio. I shared a spreadsheet using Google Docs and each student entered their calculated water and land numbers. They were assigned line numbers in the spreadsheet. (

*This also provided an quick grading opportunity for me as I was able to see missing assignments as missing data in the spreadsheet.*) As a class we examined the spreadsheet, eliminated a couple of entries that seemed to be outliers, then averaged the numbers. The student data was very nearly spot on with the numbers they quoted at the beginning of the lesson. Students were genuinely excited about their results and as a class the degree of accuracy they achieved.

**How Do We Know That?**

As the year progresses, I plan to continue with asking students how they know what they know. What evidence do they have that convinces them that the information is true. We have so much information at our finger tips. Our goal should not be limited to consumers and repeaters of facts but to challenge ourselves to understand how we know that so we can become critical thinkers and creators of information.