Friday, October 28, 2011

Fossil Records

We have moved on from plate tectonics, earthquakes and volcanoes and it is now time to move on to Life Over Time.  Over the next few weeks, we will explore how life developed on Earth, how it changed over time, and the theory of natural selection.  The very first section covers fossil evidence of earlier species.

There are three basic types of fossils that can be discovered:  parts of an organism, whole preserved organisms, or traces, molds and casts of organisms.  It is much more rare to uncover a whole organism or a part of an organism.  To demonstrate this point, we made a fossil record of our own lives and played a little guessing game to determine whose fossils we studied. 

It is worth noting that we took a few liberties here with our interpretation of "fossils."  The students selected five small objects that represented different stages in their lives - baby, toddler, early childhood, upper elementary grades, and middle school.  We made sure to discuss, however, that fossils are remains of living organisms, not objects.  Either way, students made fossils from air-dry clay of their objects then "buried" them in order of when they occurred.  The oldest fossils would be found below the newer ones.

Because I teach three sections of sixth grade science, it was easy to scramble up the samples the following day.  Each student in the class received the fossil record of another student in another homeroom.  They filled in a chart with their best hypotheses about what the imprints showed, what they represented and what they were able to learn about the person.  Finally, they made a guess about who they thought the created that record.  We revealed the guesses and made it into a fun game at the end of the second day of the lab.  

Wednesday, October 12, 2011

Explosive Volcanoes!

We are all familiar with the baking soda and vinegar model of a volcano, but only a science teacher would fixate on how little this instructs about how a volcano actually works.  Sure, it looks cool, but volcanoes really have nothing to do with some kind of substance pouring down, creating a chemical reaction and fizzing out of the top. 

Instead, we decided to model volcanoes in a more accurate, albeit messier way.  When we studied volcanoes, we focused primarily on the types of sites where volcanoes occur (convergent plate boundaries, divergent plate boundaries and above hot spots), as well as the basic parts of a volcano.  The magma/lava, afterall, comes from below the surface and as it cools on Earth's surface, new rock is created, not just a fizzy mess of baking soda and vinegar. 

Our volcanoes were constructed out of clay.  We constructed the mounds around a straw that had been poked through a paper plate and secured in place on both sides with rubber bands.  The paper plate will represent Earth's surface, the clay represents the volcano mound and the straw will become the main pipe of this cinder cone-like volcano.  Make sure that several inches of straw are exposed on the top of the plate and at least one inch below the plate.  We constructed the volcano/straw structure on the first day of the lab, then let them dry over the weekend.

When we returned on Monday, the eruptions could begin.  We created our own mock magma the same way we had for our seafloor spreading demonstration - white school glue mixed with red and yellow food dye.  Carefully using a funnel, we filled a balloon with the magma, thus representing the magma chamber below the surface.  Make sure not to overfill the balloon or it will be impossible to attach to the model.  Only fill the round part of the balloon, not the neck. 

We washed the funnels out right away to make sure that the glue did not dry, creating a permanently glued mess.  Once the funnels were washed and the balloons filled, we carefully rubber-banded the balloons to the exposed inch of straw under the plate.  It is nearly impossible to make the rubber band tight enough by wrapping it around, so I suggest using a slip or loop knot tightly around the straw.

One partner should hold the knotted rubber band and the base of the balloon around the straw while the other partner gently pumps the balloon.  The magma should flow freely out of the straw.  On their lab sheets, I asked students to reflect on where and how the lava flowed depending on the slope and roughness of the mound's surface.  They also noted that as the lava "cooled" (really it was drying), it slowed down in its flow and began to pool up in low-lying areas. 

Whenever setting these models down, we always placed them on two desks with the bottom's balloon and exposed straw poking in between the crack of the desks.  In order for the models to dry overnight, we make stacks of textbooks with cracks in between so that they could sit flat to dry.  Once all of the glue was dry, I cut the balloons and excess straw off the bottom with scissors so that the models could now sit flat for further analysis for their lab sheets. 

This was a fun way to model how volcanoes work that was a little more accurate than the old vinegar and baking soda model.  While there were plenty of opportunities for huge messes during this lab, most students genuinely wanted their model to be successful and carefully followed the directions to do so.  Once students analyzed the eruption, filled in their sheets identifying each part of the model and what it represented, and read the accompanying text, I felt that they had a far better understanding of a volcano than from the baking soda model.

Wednesday, October 5, 2011

Modeling a Seismograph

While reading through our text and completing our notes, we read about how seismographs measure the intensity of earthquakes, but there is no better way to explain it than to see one in action.

Last year, I came across a deeply-discounted model of a seismograph in one of the science supply catalogs, so we bought it.  The model is a very basic one, just a roll of paper with a stand and a mounted felt-tip pen that moves freely in response to movement. 

In class, we used styrofoam blocks cut at an angle to represent tectonic plates meeting at a fault.  We sat down around a wobbly table and created some quakes with our "plates."  Luckily for us, our classroom table is already pretty wobbly, so it didn't need much help!

We modeled earthquakes at three types of faults - normal faults, reverse faults and strike-slip faults.  The seismograph measured the intensity of each. 

Below are some images of our "quakes" in action:

Even though our styrofoam blocks made quite a mess of foam dust, it was worth it to see the students really understand how seismographs work and to let them take a break from normal classroom routines and shake things up a little!