This is the Biosphere Challenge, a long-term, problem-based inquiry designed to have students explore the systems involved in sustaining life. I practiced this challenge myself and detailed the experience below.
My Biosphere Challenge
9/5/18
Within the terrarium, I added several different soils. One layer is potting soil, bought at the store, which I mixed with loose, sandy soil collected from a grassy knoll at a parking lot. I also collected a layer of mulch, several small rocks and humus/duff like pinecones, dead leaves and needles. Altogether, the soil is about 5 inches tall within the terrarium, making roughly 1000 cubic inches (5x10x20 in) in volume within the tank, and a little over half of the tank filled. The potting soil was bought to ensure adequate nutrients for the plants I was to put in. The sandy soil to allow porosity and filtration, rocks and larger debris to allow air in the soil, and mulch to possibly prevent mold growth. I bought 3 potted mums as plants to absorb the carbon dioxide my arachnids and insects would produce, and also release oxygen for them to breathe. Along with the flowers, I planted a wild fern collected from outside my apartment, as well as a few plantains. Hopefully, these plants will be able to survive in the nutritious soil and live off the carbon dioxide produced by the insects/arachnids and decaying matter. I currently have the terrarium positioned about six inches from my window and have most of the terrarium away from direct sunlight in hopes that the sunlight will help the plants photosynthesize, but not dry out the soil or plants too much or overheat the terrarium. As far as insects and arachnids, I have in my terrarium one grasshopper, 2 mosquitos, 1 live ant/4 dead, and 4 spiders of various species. One spider has an egg sack, which I am hoping will either allow for multiple generations of new spiders or provide food for the other spiders. Although there is not a large amount of insects for my carnivorous spiders, I’m hopeful that in somewhat of a “survival of the fittest” I will have some spiders successfully catch and live off the nutrients of some of these invertebrates. My biosphere is made airtight by a cling wrap sealed and duct taped top. The cling wrap helped temporarily hold insects and arachnids as I placed them in the terrarium. I’m hoping that the rough, cloudy surface will allow some sunlight from my window into the terrarium for plants but will not reflect the sunlight intensely to overheating the terrarium and providing enough shade for my invertebrates.
Airtight or Not Experiment
To prove that my Biosphere is airtight, I used the “Balloon in a Bottle” experiment as my basis and a small-scale model of my Biosphere using a Pyrex dish. The Balloon in a Bottle experiment is one in which you insert a regular balloon into a plastic or glass soda bottle, leaving the mouthpiece of the balloon covering the lip of the bottle. When trying to blow up the balloon in the bottle, you will not be able to inflate it because of the air pressure inside the bottle—there is no more room for air from the balloon to get in when the air the bottle can’t escape. If you poke even a small hole in a plastic soda bottle, you are able to inflate the balloon because the air inside the bottle can escape from the small hole as it is displaced by the air from the balloon. My theory was that I could do this with a model of my Biosphere. I took a 10”x8” Pyrex dish, covered it in the multipurpose sealing wrap (which claims to be airtight on the box!) and duct tape it the same as my Biosphere. Before duct taping the sides, I practiced using the balloon to make sure it inflated properly, tested it in a bottle (to confirm that the Balloon in a Bottle experiment was true—and for fun), and inserted the balloon in a small hole in the middle of my sealing wrap. On the underside and topside, I sealed the balloon in place with duct tape with the mouthpiece coming out the top, making sure it could still inflate from the mouthpiece while covering the hole I made in the sealing wrap, and then laid it over the dish and duct taped the sides. From here, I attempted to inflate the balloon. Unlike the bottle, I could still inflate the balloon, which I attribute to the looseness and stretchiness of the sealing wrap, so I continued to inflate to see if I encountered any resistance or heard any air escaping. I continued to inflate the balloon and eventually reached a point where I could no longer inflate without a significant amount of effort. There was still room left in the Pyrex dish for the balloon to expand out to, so it wasn’t reaching a point where it had no more room to expand. From this experiment, and if I’m to believe the statement on the sealing wrap, I think that, beyond a reasonable doubt, my Biosphere would experience the same results and prove that it is airtight.
10/10/18
My biosphere has changed pretty dramatically over the past weeks. My mums from Walmart grew white fuzz about a week or two after sealing it, which spread all over them and turned them into decomposing goop. My one spider that I could find made a web and remained there for awhile. It was still alive for the first week or two, but I noticed it had dew drops on its web and it too grew the white fuzz on it. Where the other spiders and grasshopper went, I can only assume they ate each other and/or buried themselves in the soggy substrate or are hidden inside the white fuzzy jungle. At this point, I’ve dumped my biosphere and given my spiders a fresh air burial. After getting some expert soil opinions from Rachel Thiet, for next time, I think I will not use any Walmart flowers or store bought potting soil at all. From her opinion, the connection between soil microbes and plant roots have an important symbiosis, and just using soil from outside will probably be better. Of course, she also said that keeping these spiders alive in an airtight container is probably not possible, but there may be hope for the plants! Also, I plan to use a little less water (>3 cups) and keep some water in an impermeable dish for the spiders to drink. In terms of spider food, I think I would want to research a consistent substance that spiders could eat.
11/6/18
I’ve taken a new approach to my biosphere. I took a large chunk of soil on a wet, rainy day from the uphill side of a road. I looked for soil that had different mosses, lichen and small plants and grasses (like partridgeberry) and any potential soil organisms. I’m hopeful that this healthy forest soil will have an effective way of sequestering and releasing carbon since all the soil components have been working together before I placed them in the biosphere. The piece of soil I grabbed had some fruticose lichen, which is particularly sensitive to air pollution. I’m hoping that whether or not the lichen thrives might indicate the air quality of my biosphere naturally. Since it was so saturated, I didn’t add any water and I haven’t put a spider in yet. I sealed my terrarium the same way as before, but this time leaving it without duct tape for a day to allow the moisture to build up. I’m then planning to keep a corner ventilated so that the plants can adjust to the sealed environment. I got this idea from a video on keeping plants in airtight containers. After the moisture has released, I’ll seal it.
11/9/18
Jimmy gave us plexiglass to cover our terrariums with, and some crickets to experiment with different organisms inside our biosphere. I had 5 live crickets that I put inside. Within a relatively short amount of time, they had disappeared somewhere in the tank, probably burying themselves in the soil. I haven’t noticed any other organisms moving around.
11/28/18
I got back from two weeks away for Thanksgiving break, and found my plexiglass had bowed. I didn’t have enough weights on the corners to keep it from doing this. While I don’t think I had anything escape (I don’t hear any crickets in the house). I had kept the room temperature at 61 degrees while I was gone. I did notice that my fruticose lichen had died though! This makes me wonder if the air in my room was what caused this, which makes me question my own health! I’ve weighted down the lid, so hopefully I notice some change.
12/5/18
As my last observation before letting my biosphere critters go, I found a bee slowly crawl out of the soil and onto some leaves! I wonder if it had been in the soil preparing for hibernation, and either the warm temperature of my room or resealing the biosphere caused it to come out. It is definitely struggling to move much, so it may be in poor shape from being woken up. I’ve released my biosphere now, and looking inside, it still has a very moist, soil smell too it but no strange molds like Round 1. I looked around for the crickets, and saw no sign. Maybe the died and decomposed in the soil? Or maybe I just didn’t find them when tearing through the soil. I did find a slug, which didn’t seem to be moving when I touched it so it may have died. There was only one other decomposing bug that I found. After finding so many things, I think I would want to see what other kind of organisms would do well in the biosphere. Measuring the CO2 and temperature would also be helpful. I think using soil from a rich, natural site was the right way to go though.