Science 8 – Helgeson
Rock Cycle Journey Activity
Materials:
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White playdough (about twice as much as other colors)
Yellow playdough
Green playdough
Red playdough
Plate
Plastic knife
The Rock Story:
Read the story as you create the rocks.
Once, millions of years ago, there was a lake between some mountains. Some of the
mountains were made of white rock, some of red rock, some of yellow rock, and some
of green rock. When rain and snow fell in the mountains, the water ran down the sides
into the lake.
There was a big river coming from the white mountains, because lots of rain and snow
fell there. As the river rushed down to the lake, it tumbled over the soft white sandstone.
Some of the sandstone eroded away and got carried along by the river. It was carried
all the way down to the lake. There, the water wasn't rushing anymore, and the sand
settled down on the lake bottom. After a couple hundred years, there was a deep layer
of white sand covering the bottom of the lake.
Take half of the white playdough and pat it into a circle. Place it on your plate, the
"bottom of the lake".
Over time, the weather patterns changed. It didn't rain and snow so much in the white
mountains anymore. Instead, a lot of rain fell on the yellow and green mountains. These
mountains were steep and sometimes had landslides. The rivers and landslides from
the yellow and green mountains carried boulders down the slopes. They crashed into
the lake and sunk to the bottom.
Make all your yellow and green playdough into marble-sized "boulders". Put about half
of the boulders on top of the white sand layer, covering it up.
A thousand years later, the weather had changed again. The rain now fell on the red
mountains. The rivers that ran down the slopes caused erosion. Red clay was carried
away from the side of the mountain and down to the lake, where it sank to the bottom.
Make your red playdough into a pancake and gently set it on top of the yellow and
green boulders.
Another landslide made more boulders tumble down from the yellow and green
mountains into the lake.
Put the rest of your yellow and green "boulders" on top of the red layer.
After a few hundred more years, the weather changed again. The rain once again fell in
the white mountains. The white sandstone got worn down and carried sand to the lake
bottom once more.
Use the rest of your white playdough to make another pancake and lay it gently overtop
all the layers.
Time passed - millions of years. The lake dried up and vanished. More and more sand
and silt and boulders and earth became piled on top of where the lake bed had once
been. The weight of the earth above put pressure on the sand, clay and boulders, and
they slowly become "glued" together into sedimentary rock.
Press very gently on top of the last layer of white playdough so the layers stick together,
but aren't squished. Use the knife to cut a slice off the edge so you can see the layers
from the side. Can you see the layers of rock? Set your slice aside and keep it to
compare later.
Millions of years more passed. Below where the lake had been, a crack grew deep in
the earth. Magma, melted rock, came up from below. It pressed against the
sedimentary rock from the bottom and heated it. All the heat and pressure made the
rock change into a metamorphic rock.
Press harder on the rest of your rock layers so they squish together. Cut another slice
off the edge. Compare this slice with the sedimentary slice. How are they different?
Millions more years passed. The plates of the earth moved, and the part of the earth
where the lake had once been was pushed under another part of the crust of the earth.
As the metamorphic rock was pushed deeper and deeper down, it became hotter and
hotter. Eventually it melted, becoming magma itself.
A crack in the upper layer of the earth opened up. The magma, which had once been
the bottom of the lake, erupted out of the crack and into the open air. Now that it was
out of the earth, it was called lava. The lava flowed down the side of the volcano and
cooled off in the air. When it cooled all the way down, it was a brand-new solid
rock: igneous rock.
Take what's left of your rock, except the two slices that you set aside, and mash it with
your hands. Make it into a volcano shape. Look at the side of your volcano, and cut off a
slice if you want. How is the igneous rock different from the sedimentary and
metamorphic slices?
Time kept going by. The volcano erupted some more, but then stopped erupting. Now it
is just a mountain with a crater at the top. It rains a lot where the volcano is, though, and
as rivers rush down its sides they wear away at the igneous rock. Bits of the mountain
are eroding, being carried downstream. The cycle is beginning again...
When you're done, don't forget to clean up!