A couple new article relevant to our study of Earth History.
Carbon
Image by Rajdeep Dasgupta, via pyhs.org.
Research on the high pressure and temperature conditions at the Earth’s core suggest that most of the carbon in the early Earth should have either boiled off into space or been trapped by the iron in the core. So where did all the carbon necessary for life come from? They suggest from the collision of an embryonic planet (with lots of carbon in its upper layers) early in the formation of the solar system.
Free Oxygen
Typical surface view of purple mat surface at Middle Island showing purple filaments. Some white filaments can also be observed. Image from Thunder Bay Sinkholes 2008 via oceanexplorer.noaa.gov.
It took a few billion years from the evolution of the first photosynthetic cyanobacteria to the time when there was enough oxygen in the atmosphere to support animal life like us. Why did it take so long? NPR interviews scientists investigating purple microbial mats in Lake Huron.
Well we watched Jurassic Park last night and concluded it with a discussion about the issues underlying the movie, the same way we’ve been studying analyzing the issues underlying texts. Discrimination based on race and obesity came up first (the fat guy and the black people “always” die), but I was able to coax a bit of discussion about the role and responsibility of science and scientists. Our discussion is summarized in the graphic organizer above, but there are many more subtexts to the story that we did not have time to explore.
Jurassic Park by Michael Crichton (the book).
I like both the movie and the book because, like most good science fiction, they explore some interesting issues that relate quite nicely to the curriculum. Jurassic Park has a nice little introduction to DNA and gene sequencing that is tied to some the history of life on Earth. As works of art in their respective fields, however, I prefer the movie. The novel has a lot of wonderful detail, and the scientist in me loves the detail, but the characters are not as well drawn and the story seldom strays from its main thesis, scientific hubris. What it has to say about that issue is well expressed and well researched so it does capture the interest of the reader. (The follow-up book, “The Lost World”, sails adrift of the science, is logically incoherent and has a proportionate deterioration in the quality of the writing.) I do however recommend the original Jurassic Park book to my students as a personal novel.
Steven Spielberg makes a great movie, extracting empathetic performances from the actors. Since the book’s author, Michael Crichton, also wrote the screenplay, the movie stays true to the core issues in the text. I think its a great example of a successful, dare I say synergistic, collaboration.
Tomorrow, instead of retelling around the issues in writing, my students are going to try to do so in a skit. This could get interesting.
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.
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.
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.
I spent an hour yesterday censoring Larry Gronick’s, “Cartoon History of the Universe“. I always feel a little dirty after doing it, but the section on the origins of life, particularly the comparison of the relative advantages of asexual and sexual reproduction, does go a little too far with the puns (in my opinion at least).
I do, however, like the book a lot, especially the section on the origin of the universe and history of life on the Earth throughout the Cambrian. I tend to use the bit up till the appearance of humans about 200,000 years ago. Despite being written in 1990 the information is still very accurate. The art is excellent and a pleasure to observe.
Of course, censoring tends only to increase students’ interests in finding out what was blacked out. Fortunately, there’s nothing in the Cartoon History that’s too terrible even if they should decipher it.
Franz Lanting has a great storytelling voice and wonderful photographs that catalogue the history of life on Earth, from early organisms like stromatolites to the modern diverse forms of life (Lanting, 2007).
