Natural World – Page 75 – Montessori Muddle

Synthesizing the history of life

Sparking curiosity with the Toilet Paper Timeline, then following up with the beautifully drawn Cartoon History of the Universe seemed to work pretty well to keep students interested and engaged in their work. However, in putting it all together in their presentations we needed a simple graphic organizer to point out the highlights.

The History of Life on Earth timeline I put together to start with gives the broad overview, but we need to telescope the Cambrian to observe the really interesting, broad patterns in the evolution of multicellular life.

There are two key ideas I want students to get from these exercises. The first is what the Montessori lessons call the Gifts of the Phylum, which boils down to the fact that different Phyla represent major milestones in evolutionary development. For example, Cnidaria, the phylum of jellyfish, are important evolutionarily because they mark the emergence of organisms with endoderms and exoderms.

The second important concept regards the cycles of extinction and diversification that can be found in the fossil record. Dinosaurs emerge after the Permian-Triassic extinction event and diversify; large and small species, carnivorous and herbivorous, land based and ocean based. Similarly, after the Cretaceous-Tertiary extinction wipes out the dinosaurs, mammals take over and diversify to fill all the empty niches; elephants and mice, tigers and gazelles, rinos and whales.

Resurrecting the greenhouse

Two years ago, the middle school’s flagship project was to put up a fully functional greenhouse (using this design). It took all year but we did it. On the way, we got to practice geometry, mapping and construction, while learning and growing plants and studying soil profiles. It was so successful that, with our spring plant sale we broke even on the entire project.

Last year, however, the greenhouse was somewhat neglected. My plans to add an automatic window opener, which would have been a wonderful tie-in to our electronics and Newtonian physics studies, did not work out; we just did not have the time. We’d taken the plastic covering off, so only the bare, forlorn PVC frame was left standing around a plot of waist-high weeds.

Though I could not have predicted it, this year we have a strong core group of students who are highly enthusiastic about resurrecting the greenhouse and making it work. My suggestion was that we try to grow produce this fall that we could cook in December when we do our Dinner and a Show. Well, two weeks in, they’ve already put together a menu plan, weeding is well on its way and I’m being harassed to hurry up and arrange a trip to Home Depot. The excitement is so infectious that another student has volunteered to bring in his electric weed-whacker during the immersion. It’s amazing!

I’m having the hardest time not butting in. There is a beauty in seeing a well oiled machine executing a project or solving a difficult problem. But there is another even more wonderful aesthetic visible in a the birthing struggles of a nascent team. The forward motion of infectious enthusiasm is pulling puzzle pieces into its wake, and the pieces just seem to click into place when the time is right. I have to keep reminding myself that my job is to prepare the environment and let the kids do the rest.

Toilet Paper Timeline in practice

tp-02 — Who thinks they're at the most important event?

The Toilet Paper Timeline of Earth History worked as well as I’d hoped. The beginning was a bit boring, it was a challenge keeping the kids focused, since nothing much happens for a very long time. It helped that we had to unroll the toilet paper back and forth across the room, so I had a different student take over every time we had to turn around.

That was not quite enough though to keep them from getting distracted, however, so I also assigned people to stand at the location of major events. This worked out nicely in the end because it let me ask them, at the end, whose event was the most important? Most of them made some argument without any prompting; the group is already pretty comfortable with each other and are not afraid of speaking up.

During the unrolling, most events occur in the final two turns. Students did notice this fact, which is the ultimate point of the exercise. Getting them to talk about different events, like the time of the first multicellular organisms or the extinction of the dinosaurs, helped students own the work. All together, it seemed to strike their imaginations.

They also seem to like using Cartoon History of the Universe as their reading assignment.

tp-01 — The Pre-Cambrian. Nothing much happens for a long, long time.

Toilet Paper Timeline of Earth History

Toiletpapier — Image from Wikimedia Commons.

Jennifer Wenner has posted a beautiful demonstration of geologic time using toilet paper for the timeline at SERC. You’ll need a 1000 sheet roll and by the time you’re done there will be toilet paper everywhere.

This is a great demonstration because as you unroll the toilet paper you get a great feel for the long spans of time in the preCambrian when nothing much happens, and then, as you approach the present, events occur faster and faster. There’s 300 million years between the formation of the Moon and the formation of the Earth’s atmosphere. That’s 60 sheets! while modern man only turns up about 10,000 years ago, which is 0.002 sheets; about the width of the line drawn by a pen. Even the dinosaurs went extinct only 14 sheets from the end.

The SERC webpage has a spreadsheet with most of the important dates marked and translated into toilet paper units. The Worsley school in Canada has some nice pictures of the toilet paper being rolled out all the way down the hall.

Earth_timeline — History of life on Earth timeline (from NASA).

Living without oxygen

anaerobic-organism — Microscope image of the undescribed species of Spinoloricus (Loricifera; stained with Rose Bengal) (image from Donavaro et al., 2010)

While there are quite a number of single-celled microbes that live in environments without oxygen (they’re anaerobic), multicellular organisms have now been discovered, living near the bottom of the Mediterranean Sea, that also do not need oxygen.

(a) a hydrogenosome-like organelle. (image from Donavaro et al., 2010)

What’s really neat, and creates a great teaching point, is that these anaerobes don’t have mitochondria in their cells, so they can’t use oxygen for energy:

The creature’s cells apparently lack mitochondria, the organelles that use oxygen to power a cell. Instead they are rich in what seem to be hydrogenosomes, organelles that can do a similar job in anaerobic (or oxygen free) environments. – Vogel, 2010.

The conclusion paragraph of the journal article, would make a nice piece for students to mark up and process. It might even work better for use on a vocabulary test because you’ll need to understand the vocabulary to understand the text.

This is the first evidence of a metazoan life cycle that is spent entirely in permanently anoxic sediments. Our findings allow us also to conclude that these metazoans live under anoxic conditions through an obligate anaerobic metabolism that is similar to that demonstrated so far only for unicellular eukaryotes. The discovery of these life forms opens new perspectives for the study of metazoan life in habitats lacking molecular oxygen. – Donavaro et al., 2010)

The article, by Donavaro et al., (2010) also has an intriguing image of suspected “endosymbiotic prokaryotes”. Some organelles in cells are believed to have once been separate organisms that developed symbiotic relationships with their host cells. It’s nice to see an example of it in real life. Even if it’s a bit hard to interpret.

The ultimate implication of this discovery, is that there are probably a lot more anaerobic environments on other planets so the chances of finding extra-terrestrial multi-cellular life might not be as low as we’ve thought.

Amazing storm

I appreciate how much you more of the weather you can observe using time lapse photography, but its astonishing when you don’t even need the time lapse.

While this storm seems like something out of the movie “Day After Tomorrow”, I wonder how much more freaky weather we’re seeing just because of the new ubiquity of video cameras.