Middle and High School … from a Montessori Point of View
Video by Tobais Friedrich out of the University of Hawaii. It’s based on a recent paper that suggests that the large fluctuations in climate over the last 120,000 years opened and closed green corridors that allowed multiple pulses of migration out of Africa.
He has some other excellent earth science scientific visualizations.
A couple new article relevant to our study of Earth History.
Carbon
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
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.
Here is Today is a neat little interactive website that helps put the geologic timescale, and homo sapiens’ place in it, into perspective.
With a larger class, and quite a bit of space in the gym, I had more flexibility working on the toilet paper timeline compared to the last time.
I built in a friendly race to see which group could find a set of events first, and allowed me to highlight nine different, important, series of events along the timeline.
The adapted spreadsheet, racing sequences, and a short summative quiz are on this Toilet Paper Timeline spreadsheet.
I broke the class up into 4 groups of 4, and each group created their own timeline based on a handout.
Then, I gave each group a slip of paper with four events on it (one event per student), and they had to race to see which group would be first to get one person to each event on the list. Once each group got themselves sorted out, I took a few minutes to talk about why the events were important and how they were related.
Table 1: The series of events.
| 1) We’ll be talking about plate tectonics soon, so it’s good for them to start thinking about the timing of the formation and breakup of the supercontinents. | |||
|---|---|---|---|
| Event 1 | Event 2 | Event 3 | Event 4 |
| Formation of Rodinia (supercontinent) | Breakup of Rodina | Formation of Pangea | Breakup of Pangea |
| 2) This sequence emphasizes the fact that most free oxygen in the atmosphere comes from ocean plants (plankton especially), and that a lot of free atmospheric oxygen was needed to to form the ozone layer which protected the Earth’s surface from uv radiation, which made the land much more amenable to life. Also, trees came way after first plants and oxygen in the atmosphere. | |||
| Event 1 | Event 2 | Event 3 | Event 4 |
| First life (stromatolites) | Oxygen buildup in atmosphere | First land plants | First Trees |
| 3) Pointing out that flowering plants came after trees. | |||
| Event 1 | Event 2 | Event 3 | Event 4 |
| First life | First land plants | First trees | First flowering plants |
| 4) The Cambrian explosion, where multicellular life really took off, happened pretty late in timeline. Longer after the first life and first single-celled animals. | |||
| Event 1 | Event 2 | Event 3 | Event 4 |
| First life (stromatolites) | First animals | First multicelled organisms | Rise of multicelled organisms |
| 5) Moving down the phylogenetic tree from mammals to humans shows the relationship between the tree and evolution over time. | |||
| Event 1 | Event 2 | Event 3 | Event 4 |
| First mammals | First Primates | Homo erectus | Homo sapiens |
| 6) More tectonic events we’ll be talking about later. | |||
| Event 1 | Event 2 | Event 3 | Event 4 |
| Opening of the Atlantic Ocean | Linking of North and South America | India collides with Asia | Opening of the Red Sea |
| 7) Pointing out that life on land probably needed the magnetic field to protect from the solar wind (in addition to the ozone layer). | |||
| Event 1 | Event 2 | Event 3 | Event 4 |
| Formation of the Earth | First life | Formation of the Magnetic Field | First land plants |
| 8) Fish came before insect. This one seemed to stick in students’ minds. | |||
| Event 1 | Event 2 | Event 3 | Event 4 |
| First Fish | First Insects | First Dinosaurs | First Mammals |
| 9) Mammals came before the dinosaurs went extinct. This allowed a discussion of theories of why the dinosaurs went extinct (disease, asteroid, mammals eating the eggs, volcanic eruption in Deccan) and how paleontologists might test the theories. | |||
| Event 1 | Event 2 | Event 3 | Event 4 |
| First Dinosaurs | First Mammals | Dinosaur Extinction | First Primates |
The whole exercise took a few hours but I think it worked out very well. The following day I gave the quiz, posted in the excel file, where they had to figure out which of two events came first, and the students did a decent job at that as well.
In the early solar system, 4.5 billion years ago, the planets were still coalescing, something enormous hit the Earth.
After it formed, huge impacts shaped the surface of the moon into what we see today. NASA takes up the story:
These videos are awesome introductions to the early history of the Earth, Moon, and solar system.
65 million years ago, an asteroid hit the Earth just off the Yucatan Penninsula, kicking up enough dust in to the atmosphere (and perhaps setting off supervolcanos) to lead to the extinction of the dinosaurs. Geologists mark this mass extinction event as the end of the Cretaceous period and the beginning of the Tertiary; it’s called the K-T boundary. Paleontologists see a rapid change in the forms of life fossilized in the rocks above and below the boundary. The element iridium, which is relatively common on asteroids, but rare on Earth, can be found in a thin layer of the fallout from the asteroid impact all around the world.
Well, the Earth’s going through another mass extinction event right now. In fact, even if humans were to go extinct right now, the remains of our cities and our impact on the global chemical cycles, will leave a distinct signature that geologists millions of years from now will be able to detect.
Geologists refer to the last 10,000 years, the period starting when the Earth warmed after the last glacial maximum, as the Holocene. This time period saw the emergence of agriculture, the rise of human civilization, cities, nuclear weapons, the internet. Now, given the enormous environmental changes we’re wrecking on the planet, some say we’ve entered a new geologic epoch that they’re calling the Anthropocene.
The question is: How long will it last?
Regardless of your philosophy, the recognition that we have entered a geologic age of humanity raises the obvious question of just how long such an age will last.
In the infamous KT boundary geologists can see evidence for a rather short-lived event that also reshaped the planet. Sixty five million years ago an asteroid struck the Earth, driving one of only five mass extinctions in the planet’s history. The loss of the dinosaurs turned out to be an opportunity for our mammal ancestors and led directly to our own age.
Since the Anthropocene appears to mark a sixth great extinction, one has to wonder what it will take for us to make it out of own era with civilization intact.
— Frank (2011): The Anthropocene: Can Humans Survive A Human Age?
Collecting the amazingly well-preserved Cretaceous molluscs and arthropods at the Coon Creek Science Center was an excellent way to learn about fossils and the geology of the Mississippi Embayment.
Consider: the actual shell of an actual organism that actually lived 70 million years ago; not the form of the shell, petrified in silica; not the silent imprint of ridges and grooves in the mud of some bivalve’s test, long dissolved by the silent flux of millenia of groundwater flow, although you can find those, too; but to stand in the daylight, on the gravel bar of a creek, and hold the actual shell of an actual marine organism that lived here when it was six meters under water.
When we got to Coon Creek, Pat Broadbent did her typical, excellent presentation, starting with the very basics question of, “What are fossils?” Apart from the aforementioned actual preserved shells, you can also find trace fossils, like, for example, where the imprints of the an organism is left in the mud while the shell itself has long dissolved away. They can be imprints, or molds of the shells. One of my students found the mold of a crab’s claw along the creek bed; the mud filling in the claw had solidified into rock but you could clearly see where the pincer once articulated.
Pat also talked about the Mississippi Embayment, which is the long, broad valley through which the Mississippi River flows.
When the supercontinent Pangea started to break up, North America pulled away from Europe and Africa. This created a rift that eventually became the North Atlantic Ocean. At about the same time, North America tried to split into two as a second rift was created, right where the Mississippi Embayment is today.
But the rift failed (Cox and Van Arsdale, 2007). It did, however, stretch and thin the continental crust enough to create a large inland sea running up the middle of North America. Over the 100 million years since, the rift formed, the Mississippi Embayment has filled in, first with oceanic sediment, but then with terrestrial sands and silts as the mountains to the east and west were eroded away and washed into the inland sea.
The layer of silt and glauconite clay that encases the fossils at Coon Creek is called the Coon Creek Formation. Pat was very clear that we should refer to this material surrounding the fossils as “matrix”. The “d” word was prohibited. These sediments were deposited while the sea still flooded the embayment. They formed a sand bank, several kilometers offshore.
I vaguely remember doing some research on glauconite a long time ago. Glauconite pellets are found in shallow marine waters, usually far enough away from the coastline so that sediment is deposited slowly, and it’s the finer materials, such as silts and clays, that are deposited. The water also needs to be deep enough to protect the fine sediment from the force of the waves. These are ideal conditions for clams, mussels, conchs, and their Cretaceous relatives.
A simple smear of the sediment across a microscope slide is enough to show that the matrix is has a lot of quartz. You need a microscope because the mineral grains are tiny, silt sized or smaller.
But the best part of looking at the slides is finding the microscopic fossils. They’re not as ubiquitous as you might think, but they’re there if you look. I found a couple of forams, a snail-like one and another that looks like a bolivina species.
However, the smear slides came later. After Pat’s talk, she took us out to a small mound of matrix that had been excavated for sampling. Everyone grabbed chunks of matrix and pared away at them until they found something promising. These promising samples were wrapped in aluminum foil so we could clean them up under more controlled conditions.
Cleaning takes time and patience, so Pat showed us how to do it, and each student worked on a single sample. The main idea is to create a display of the fossil using the matrix as a base. The general procedure is to:
After the instructions on cleaning, we broke for lunch. For most of us lunch could not have come early enough, not because we were particularly hungry, but because it was quite cold outside. Just the week before the temperature had been above 20 °C, t-shirt weather. Now students were clustering around a couple space heaters trying to ward off frostbite (or at least that’s what they claimed). I did offer that they could stay inside after lunch while the rest of the class walked along the creek, but no-one took me up on it. I don’t know if it’s specific to this group or just to adolescents in general, but if there a chance to walk through water, and get dirty and wet, they’ll take it no matter what the consequence.
Walking the creek, pulling shells and molds out of the gravel bars, was the best part of the visit.
The water was shallow, not getting up above the shins, despite the rain showers of the preceding days. A few students borrowed rubber boots, which half of them proceeded to fill with water.
There were quite a lot of fossils. Some of the bivalves have really thick strong shells that not only survived the 70 million years since the Cretaceous, but being washed out of the matrix and tumbled down a stream bed with all sorts of sand and gravel. Some of the casts, like the aforementioned arthropod claw, are also pretty robust.
A couple of the more interesting finds are the rather elongate tube like structures that are believed to be either fossilized burrows, or fish feces (coporolite). The material in the coporolite has been replaced by minerals, which is why it survived, but it still retains a little of the ick factor.
There’s an awful lot to learn at Coon Creek. I did not even mention the mesosaur skeletons that have been found there, but there is a nice IMAX movie, Sea Monsters, that’s a nice complement to the field trip because it’s set at the same time, and in the same marine environment as the Coon Creek Formation.
