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2020 Kathryn Gregory Wodzicki

The Rock Cycle:

Second Closed System Experiment

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Closed System Experiments

Today we will continue to explore the question of whether volcanic eruptions add mass to the earth.

In our first experiment, we investigated what happens when a rock weathers (breaks down) in a closed system. In our second experiment, we will explore what happens when new rocks form (crystallize) at the earth’s surface.

Eruptions at Mt. St. Helen’s, USA, and Mt Rinjani, Indonesia

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Beans in a Jar: Growth

It’s not easy to imitate a volcanic eruption in a mason jar, but we can look at something else that grows at the Earth’s surface: plants.

In this experiment, we will put bean seeds in a sealed jar to try and understand what happens when we see something new form at the earth’s surface.

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Experiment 2: Beans in a Jar

We soaked some bean seeds in water for 24 hours, then put them in a baggie with a moist piece of towelling to sprout.

We took four of the seeds that sprouted for our experiment. Watch the video to see how we set it up:

Starting weight, four seeds: 9g

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Seedling growth

Day 2

Day 4

Day 6

Day 7

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What is happening in the jar?

We can think of a seed as a baby plant (embryo) in a box (the seed coat) with its lunch (nutrients). The plant embryo can grow its first set of leaves using the nutrients stored in the seed.

plant embryo

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Photosynthesis

Once the seedling grows leaves, it can then use energy from the sun, carbon dioxide in the air, and water in the soil to grow. This process is called photosynthesis.

The plant gives off oxygen.

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End of Experiment

At the beginning of the experiment, we planted four seeds, which together weighed 9 grams. Three of the seeds grew, and at the end of the experiment, the seedlings weighed 19 g.

However, the weight of the jar did not change!

	Start of experiment	After 9 days
Seeds	9 g	19 g
Jar	1015 g	1015 g

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Interpreting the data

So what happened? We saw the seedlings grow and get bigger, yet the jar did not change weight.

Recall that during photosynthesis, plants use sunlight, oxygen, and water to grow. Because our jar was sealed, the seedlings used particles of carbon dioxide and water that were in the jar to get bigger. The weight of the jar did not change, because the seedlings used material inside the jar to grow.

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Box of Lego comparison

Think of it this way. Say you get some Lego. The pieces weigh 500g. If you build a house with all the pieces, the house will weigh 500g. You have not added or subtracted any pieces of Lego; you have just rearranged them.

If you then take apart the house and build a plane with the same Lego pieces, it will also weigh 500g

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The Earth Recycles

These experiments help us understand what is happening on Earth, which is a closed system in terms of matter. If a volcano explodes and forms a basalt, or if a limestone erodes in the rain, the Earth is just “rearranging the lego.” The lava that formed the basalt came from melting another rock. The material that weathered from the limestone goes into the ocean and eventually forms a new rock on the ocean floor.

This recycling process of one rock becoming another is called the rock cycle. Sedimentary, igneous, and metamorphic rocks can all change into each other.

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The Rock Cycle

You can learn more about how the rock cycle works by watching this video from Khan Academy:

You can also explore the University of Oxford Museum of Natural History Rock Cycle website.

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Reflection

Let’s pause here to reflect on our second experiment, growing beans in a jar.

Try this: Try explaining in your own words the following:

Why did we do this experiment?
What did you observe?
What did you learn?
What new questions do you have after doing the experiment?
What do you think now about whether volcanic eruptions add mass to the Earth?

When you are done, you can move on and learn more about weathering and erosion.

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Want to learn more?

Do you have any dried beans at home in your pantry? You can try dissecting one, or you can sprout them in a jar or plastic bag.
Explore the periodic table of elements, the universe’s “Lego”
If you have some old crayons at home, you can try making your own crayon rock cycle. You will need some help from an adult.

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Acknowledgements

Reflection questions modified from Klentschy, M., Using science notebooks in the classroom, NSTA Press, and “Structure and Properties of Matter” Teacher’s Guide, McCraken County Public schools: http://www.mccracken.kyschools.us/Downloads/2%20NGSS%20UNIT%20Matter.pdf

Photo credits: Title slide: Biosphere 2: Colin Marquardt / Public domain; Mt. St. Helens: Public Domain, https://commons.wikimedia.org/w/index.php?curid=260607; Mt. Rinjani: Oliver Spalt / CC BY-SA (https://creativecommons.org/licenses/by-sa/3.0); Earth: NASA/GSFC/Reto Stöckli, Nazmi El Saleous, and Marit Jentoft-Nilsen / Public domain; Photosynthesis: By At09kg : originalWattcle : vector graphics - This file was derived from: Photosynthesis.gif:, CC BY-SA 4.0, https://commons.wikimedia.org/w/index.php?curid=49183032; Lego: By Arto Alanenpää - Own work, CC BY-SA 4.0, https://commons.wikimedia.org/w/index.php?curid=44710665; Recycling symbol: By Users Cbuckley, Jpowell on en.wikipedia - Originally from en.wikipedia; description page is (was) here01:07, 31 May 2006 Cbuckley 777x733 (1,998 bytes) (== Summary == Universal recycling symbol outline version with green (#009900) fill.)17:06, 30 May 2006 Jpowell 767x723 (2,670 bytes) (Author: Chris Buckley), Public Domain, https://commons.wikimedia.org/w/index.php?curid=825615;