Hydrosphere: Water on Earth
Lesson 7 of 14
Objective: SWBAT graph the amount of water available on Earth.
The Why Behind Teaching This
Unit 5 covers standards relating to Earth's Systems. It covers Standard 5-ESS2-1: Develop a model using an example to describe ways the geosphere, biosphere, hydrosphere, and/or atmosphere interact. Students will be learning the difference between each of the systems, and ways that each of the systems interact to help make Earth what it is today. The other standard covered is Standard 5-ESS2-2: Describe and graph the amounts and percentages of water and fresh water in various reservoirs to provide evidence about the distribution of water on Earth.
Modeling will be an important component of this unit. Students will be modeling layers of Earth, the water cycle, land forms, and more. The unit begins with an overview of all the systems, then each system is taught in isolation. As each new system is covered, how it depends on or interacts with the previous systems will be addressed. In addition to the end of unit assessment, there will also be a culminating activity where groups build a model to demonstrate how 2 of the systems interact. Connections to several previously covered standards will also be made throughout this unit.
This specific lesson covers standard 5-ESS2-2 directly because students are required to graph the distribution of water on Earth. We differentiate between freshwater sources and saltwater sources prior to graphing so students have an idea of what areas fall under each category. They research the term reservoir so they understand that it is a natural or man made lake or pond that holds water for use.
The goal of this lesson is for students to be able to graph the distribution of water on Earth accurately.
Students will demonstrate success of this lesson goal by accurately graphing percentages of water in various reservoirs on Earth.
Preparing For The Lesson:
- A globe that can tossed around
- A data collection chart with two columns, one headed "Land" and the other headed "Water". I created mine on chart paper.
- A pie graph showing that about 70% of Earth is covered by water and 30% by land.
- 2 laptops for each group
- a large sheet of paper for each group
- a copy of the Graphing Water On Earth for each group
- Students will be presenting their graphs so no additional materials are needed
I have a data chart that is divided into 2 columns, one titled land and the other titled water. I choose one student to be my data collection person who goes up to the front board and stands at the data chart. The remaining students in the class stand in a large circle. The students toss a globe across the circle to each other and shout out if their thumb lands on land or water. As they shout "land" or "water," the data collection person adds a tally to that side of the data chart.
As you can see in the video of students tossing the globe, students call out the name of the person they are tossing to so they know they are prepared. The video 2 of students tossing the globe continues to show how the activity proceeds.
The data collection person adds tallies and is suppose to tell us when we have reached 100 tosses. The reason I choose to do 100 tosses is because it converts easily to a percent. The students ended up doing 110 tosses because the data collection student lost track of what number we were on. The data collection person tallies and find a total of 66/110 that landed on water, that is 60% and 44/110 that landed on land which is 40%.
Place value including decimals represented as a fraction is a concept that relates to what we have done in math with changing a fraction over 100 into a decimal and then changing it into a percentage. This provides me with an opportunity to review the math concept, as well as make a connection between the two subjects for students to see how they interconnect. I provide all students with a sticky note and ask them to calculate the percent. Since this was out of 110 and not 100, I only had about 6 students that ended up with the correct answer. I post those on the data collection chart and work out the problem for the rest of the class.
Creating a Pie Graph From Our Results
Pie graphs are something my students have not been exposed to. I draw a large circle on the front board and tell them that we are going to use our data to create a pie graph. A pie graph is a circle and the entire circle equals 100% of whatever is being graphed. I divide the graph into fourths and we discuss what percentage each fourth would equal. I find that beginning with fourths is easy because it is easy for students to compare 100% to $1 and they know that 4 quarters or 25% make up each fourth. We discuss how two quarters is equal to 50% and that three quarters is equal to 75%. The 60% that represents water should be almost right in the middle of 50% and 75% and the remaining part would represent the land.
As we look at the pie graph we created, I pose the following question to the class: Since the globe is a model of the Earth and is supposed to be a representation of the real thing, do you think this percentage is a reflection of how much water is on Earth? Students say that they believe it is close, but not exact.
What Percentage of the Earth Really is Covered by Water
I show students a pie graph showing the actual breakdown of water versus land. I access a pie graph online for ocean biomes at that shows about 71% of the Earth is covered by water and the other 29% is covered by land.
Picture from ecooceans.weebly.com
Based on this graph, were our results from the globe toss activity pretty accurate? Many students say yes, pretty close. Some disagree. After we discuss how out of 100 tosses, we were only off by about 10. This makes it seem much closer to those who disagreed.
I ask students to name some places that water can be found. They name oceans, rivers, lakes, canals, and ponds. I tell them that there are a few other places water can be found that they did not mention, like streams, groundwater, and reservoirs.
I tell students that water in all these locations can be classified into two categories, freshwater and saltwater. I draw a t-chart on the board and ask students which locations would fit under each category. I record as they tell me oceans goes under salt water and everything else goes under freshwater. They tell me that they do not know what reservoirs are though. I knew this would be a term they were not familiar with so I have included researching this in the next activity.
Researching and Graphing
I provide each student with a copy of the Graphing Water On Earth worksheet. The first thing on the sheet is to find the definition of a reservoir so that they are familiar with the term. After that, there is a section for them to record 3 websites with the information they find when they are researching. Their last task is to use the information they have found to create a pie graph showing the distribution of water on Earth.
I leave the pie graph showing that 71% of the Earth is covered by water and 29% land, up in front of the class as an example to refer back to. I remind students that the entire circle represents 100% so everything making it up should total 100%, in my example 71% + 29% = 100%. I tell them a good strategy when they are planning their pie chart is to make sure their sections add up to 100%. Although they have the task of creating a pie graph, how they interpret the distribution of water on Earth has many possibilities. I tell them that if they have questions to come ask me.
I do not want to lead them too much because I want to see what they can come up with. They could choose to graph saltwater versus freshwater, oceans versus all the types of freshwater reservoirs, or any other interpretation they find on the internet. Since I do know that no matter how they choose to graph it, saltwater will appear the same in all graphs, I ask all groups to make this blue in their graph. They can choose any other colors for the other sections. Groups may graph their saltwater sections differently but oceans would be the only thing in saltwater so it would remain constant at about 97%. Having them all shade in the saltwater the same, will make it easier to compare the graphs later.
Each group has two laptops to use for research. While they begin researching, I pass out a large sheet of paper to create their pie graph on. I circulate to listen to conversation, ensure all groups are on task and that everyone is participating.
Each group holds up their pie graph and quickly explains it to to the class. I then have them hang their poster on the front board so we can compare them all. The majority of groups created a pie graph showing 97% saltwater and 3% freshwater like the one below.
One group divided the freshwater section of their graph into two parts, one labeled ice and the other labeled freshwater. Because this group had completed their graph in this way, I was able to discuss that how the frozen freshwater is not usable by us for things like drinking, bathing, washing clothes, etc. This helps paint a better picture of how much water is truly available to us, only about 1%.
Another group started their graph by dividing into 71% water and 29% land. As I circulate the room I notice this and question how this represents the water on Earth. The group explains that they are going to divide the 71% for water into 2 sections, one for freshwater and one for saltwater. I had not considered a graph being divided in this way, however it would meet the lesson goal so I let them continue. Their final product is shown below.
We discuss similarities and differences between graphs that the groups have created. Having the one divided into land and water made it more difficult to compare to the other but I thought it was an interesting take on the assignment. It also allowed students to see how much freshwater there was in comparison to both land and saltwater. When comparing all others, it was clear that almost the entire circle of all of them was shading in to represent saltwater. Each graph had only a tiny triangular section to represent the freshwater.