How Much Water?

Teaching Kids that the Earth's surface is covered with mostly water is one of those things that is a basic piece of knowledge they are expected to obtain at some point in the science or geographical education.  This was an activity I regularly used in my sixth grade classroom (doubled as a lesson for practice with calculating percents as well) and have used in my home school classroom with my daughter (first grade) with great success.  This is a great lesson to do prior to "A Drop in the Bucket" (The directions for which are soon to follow).

Minimum Prior Knowledge:

To complete this activity at its most basic level kids must be able to:

• Differentiate between ocean and land surfaces on Earth.
• Understand that a globe is a model (like a "toy version") of the world.
• Count to 100.
• Keep a Tally
• Need to have been introduced to the Scientific Method.
• If you will expect the child(ren) to calculate percents, they will have needed an introduction.

Materials:

• First, you'll need an inflatable globe (beach ball painted as a map of the world) for every three to four children in the group with whom you will do this activity.
• paper or composition book for each student
• pencils
• Two or more People including yourself.

Time:

How long this will take will depend somewhat on the age of the children with which you are working, but the whole lesson will take about 40 minutes minimum.

To Do:

Start by asking kid(s) if they know the four oceans.  Write a list on the board.  Then, make a second column and list the continents.  Now ask the kids whether they think more of the Earth's surface is covered by water or by land.  Because of the list you just made, many of the kids are likely to answer land.  This is GREAT.  Just write it down on the board  (or paper) as a hypothesis option as well as the opposing answer that most of the surface is water.

Bring out one of the globe beach balls and ask the kids to look at it to decide on which answer will be their final choice while you turn it around for them slowly.  Point out each of the four oceans and the continents as you turn the globe.

Have your child or students copy down the hypothesis they think is true in their lab books or on their paper.

Now, with a volunteer student, play catch.  After each "catch" figure out whether your index finger (of a pre-determined hand) is on land or on water (ocean, sea, lake - doesn't matter.  If a finger is on both, just re-toss).  Tell the learner(s) you expect about 75 of the tosses to land on one and 25 to land on the other (clarify this is a giver or take kind of a number).  When you get to one hundred tosses that count it will most likely be something around 75-water, 25-land.  If you are doing percentages, have your child/class calculate the percentage. 

Have your child(ren) tell you whether your experiment shows that there is more water or whether it shows that there is more land.  It is likely your child(ren) will wonder if you just got lucky or not.  Take them all outside and set a few ground rules to help with management (do what you need to in order to pre-emtively prevent balls from going over fences, dodge ball games from beginning etc.  For example, you may remind them what a "gentle toss" looks like and specify you expect only these kinds of throws). 

If you have a whole class, have the kids break into smaller groups of 3-4 kids and try the experiment again.  Each group will need a record keeper to keep a running tally for the group of "land" vs. "ocean".  If your kids will be doing percentage practice, just give them a certain amount of time and when time is up give them 5 minutes to make sure every one in the group has the data.  Go back to the classroom and give your kids a little time to calculate their percentages.  A member from each group should then report its number findings and percentage to the whole class.  For homework, have the kids calculate the whole class percentage (showing their work) and then analyze the results and write a conclusion that states whether or not the test showed there to be more surface covered with water or with land.

If you have younger kids, have them report their numbers to you and calculate an entire class percentage for them.  Discuss with them what the numbers mean in terms of more water or more land.  Go ahead and talk to them briefly and simply about "percentage" just describing that it is a way of saying "this many times out of one-hundred" or as a way of saying, "if the world's surface was in 100 pieces, this many would be covered by water and this many would be covered by land".  Have the kids copy the class conclusion about water or land into their science logs or onto their papers.

A Great Resource for Follow Up Ecological and Science activities about water and water use.