SNS: A Density Lab....Concerning the Earth

It has been really nice covering Earth Science on Earth Day....wish I had gotten the chance to do something about Earth Day.  In my 6th grade class, we are going into more depth about the layers of the Earth and starting to understand plate tectonics. 

This week started with me showing them a hard-boiled egg, cracking it on the table, going over the cracks with a permanent marker and having the students draw and relate it to what they know about the earth.  They knew that the shell represented the crust, but then I asked "Well what about these cracks?"  Most of them could come to the conclusion that it was the plates.  After drawing, labeling and writing in our journals, I gave them a puzzle of major plates of the world, that they had to cut out, piece together and color. You can find a lesson similar to what I used here. 

Okay so Leslie... where does this LAB come in???  Hold on... I am getting there.   I promise! :)  

Anyway, after we talked about the plates and used Longitude and Latitude to locate points and determine what plate it was (love it when I can tie in another content area), we were ready to talk about the types of crust of the Earth.... Oceanic and Continental.  The kids came to the quick conclusion that continental crust was land and oceanic crust was the crust on the ocean floor.  Now here is the LAB:
I informed my students that there were all sorts of rocks in the crust, but 2 of the main were granite and basalt.  Their task was to determine which one was mostly in the oceanic crust and which one was the continental.  We drew a little picture in our journal and I asked them what they knew about the 2 crusts.  After a little jogging, they determined that the oceanic crust would be more dense than the continental crust since it was deeper than the continental crust. 

In their lab, they had to determine the density of both rocks using water displacement to find volume and measuring the mass.  We covered density IN DEPTH earlier this year and had used water displacement before.  I was proud of them for remembering and how eager they were to figure out which was which.

After they determined the density of each rock, they recorded it on a whole class data chart that I put on the board.

When all was done, we compared our whole class data.  We talked about how this experiment was repeated by 5 different groups all with different rocks and the same results were found: Basalt had a higher density than the granite.  What does this mean?  "Mrs. Johnstone, basalt must be the oceanic crust since it is more dense! "

Write! Write! Write your thinking!!  What did we do?  What were the results? How did we determine this?  All recorded in their journal. 

I worry about what will happen to these journals over the summer.... I pray they don't end up in the trash.