We figured out a bit more clearly how to translate years into distances for our Timeline For Planet Earth project. The Hadean and Archean Eons were front and center today. Fossil bacteria point to the emergence of life on Earth somewhere around the beginning of the Archean eon, 4 Gya.
Assignment:
The early development of planet Earth, especially the impact with Theia, a Mars-sized planet that hit Earth about 4.5 Gya, was the main focus today.
We are going to learn some of the history of Earth. One of the ways that we will do this is to construct as a class a timeline of Earth's history, beginning with the formation of our Solar System, marked by the time our Sun began to fuse hydrogen into helium in its core, about 4.6 billion years ago. Our timeline will be 11 m in length, so all 4.6 billion years will have to fit along this line. The first mark on the timeline will be the formation of Earth itself. As we found out today, that appears to be 4.5 billion years ago. We will outline some of the arguments that lead to these ages now and in Chapter 21, 'Stars, Galaxies, and the Universe.'
Assignments:
The Scablands of Washington state are a remarkably eroded. But how? That's what this NOVA episode is about. How were the Scablands formed, and how did the science community do its work? Sometimes it worked better than at other times. Dearly held beliefs compete with empirical evidence. Just as with Wegener's idea about continental drift and Alvarez's idea about an asteroid impact that killed the dinosaurs, beliefs closed geologists' minds to the empirical evidence that supported a very different idea. Is this good, or is it bad? Assignment:
A dramatic example of erosion in Arizona is Antelope Canyon. The picture below shows the canyon from inside. The video below the picture shows what it looks like from the ground surface at the top of the canyon during a flash flood; it sort of just looks like a crack in the ground, doesn't it! But this video was taken during a flash flood that went through the canyon. Remember, the canyon is 30 to 40 feet deep. All we are looking at is the top! Pretty violent! Rivers flow faster in some situations and slower in others. Rivers flow at different speeds in different places within their currents. As a result, erosion is greater in some locations than in others. One effect of this is that rivers meander. It's what rivers do, given enough time. We can see this happen over about 28 years in the YouTube videos linked below. Can you find the cut banks? the point bars? the oxbow lake? the cutoff? Assignments:
Erosion and deposition are important processes in shaping Earth's surface, and not only Earth's but also Mars. We'll stick to Earth, though.
Erosion is our new concern, and we learned four different agents of erosion today. What are they? We noted that Marcus Landslide in our very own McDowell Mountains is a notable local example of erosion which occurred about 550,000 years ago. And as we know, boulders still tumble down hills and mountains from time to time. And then there are floodplains, a source of concern and some controversy here in Scottsdale and Phoenix. We'll have more to say about that. Assignments:
We wrapped up our work with weathering and soil formation with a quiz today.
Wind, water, ice, and gravity all are causes of erosion, the movement of weathered material. Scottsdale has its flood fans and washes. Are flood fans 5 and 6 really a flooding threat? It seems they haven't had a flood in over 10,000 years! We also saw some spectacular examples of gravity's work today! Landslides, mudslides, slump, and creep filled our time today. I hope it wasn't too creepy!
Assignment:
We finished up or discussion of weathering and erosion today. We also began discussing the way that soils develop.
Assignment:
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Earth ScienceMr. Swackhamer Archives
March 2020
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