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Earth Science

Middle School Biology 17 – Time

We started class with “A Brief History of Geologic Time” by PBS Eons and :Great Minds: Mary Anning, The Greatest Fossilist in the World” by SciShow.

I also brought out some fossils of horn coral, heliophyllum halli, that we have and explained how they have growth ridges, kind of like tree rings. Scientists count the growth ridges and find 400 ridges per year (roughly a centimeter of growth) and since they produce one growth ridge per day that tells us that a year on earth used to consist of roughly 400 days, not the 365 days we have now.  This is because the earth’s rotation is slowing down so the Earth goes through fewer rotations in a one trip around the sun.

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Horn coral fossils showing growth ridges.

We then talked about the different ways to determine the age of a fossil, relative dating, img_1629index fossils, and radioactive dating.  The students did an activity from Real Science Odyssey Biology 2 where they cut out strips of paper that had different animals/plants on them and put them in order the way they would expect to find the fossils in the layers of earth – oldest fossils (simplest organisms) at the bottom and animals resembling what we see living on earth now, at the top.  They glued these into their notebooks after confirming they were correct.

The second activity was about radioactive decay and carbon-14 dating.  Students were each given a cup of chocolate candies, M&Ms, and dumped them on a paper plate.  All img_1628the candies that landed with the M facing up were ‘decayed’ and disposed of (eaten or placed in a separate bowl).  Students counted the remaining candies and recorded it in their data table.  They put the candies back in their cup and tossed them again and again until they were out of candies. We put everyone’s data on the white board and added all the results together and made a bar graph of the results.  The graphing part of this activity was the hardest part. Just about everyone had trouble making the axes of the graphs, not sure how many squares to use, not being consistent in the number of squares, ie just randomly putting numbers on the side of the paper.  Its really good to make the students graph by hand and learn how to do this and to check their axes before they start plotting the data.  You can find lots of different versions of this activity on the web, I used the one here on the AAAS website, Radioactive Decay: A Sweet Simulation of Half-Life.img_1630

Here’s a video explaining carbon dating.

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Big History 015 – Rocks!

IMG_1454This was the last class before break and the last one on Earth science.  We started class by making sedimentary, metamorphic and igneous rocks with starbursts.  The kids started with 3 starbursts of different colors and cut or ripped them into little pieces.  IMG_1457By lumping these ‘sand’ particles together and pressing lightly they had a sedimentary rock… made of sediments.  Then the students warmed up their starbust rock in their hands and pressed it between wax paper – putting all their weight on it.  Now its a metamorphic rock.
IMG_1460Finally we took one student’s ‘rock’ and placed it on a hotplate to melt it, making ‘magma’, then let it cool into an igneous rock.  You can find lots of videos of this activity on youtube.

The kids taped a picture of the rock cycle into their notebooks along with the data table for the next activity – identifying mineralsdiagram rock cycle.

I have two  mineral sets, one small one I bought to go along with Real Science Odyssey by Pandia Press many years ago and a large one with over 75 minerals.  Both kits came with streak plates and iron nails when I bought them.  The kids worked together in small groups trying to identify the minerals I gave them.  Each mineral has a small sticker on it so we can look it up at the end of class to see if they were correct.  I took the lab straight from Real Science Odyssey Earth & Space Level 1.  IMG_1461The students wrote down a description for each mineral, color, luster, whether it was magnetic or had crystals, what color streak it made on the plates and then they tested the hardness of the mineral.  You do that by comparing it to objects with know hardness, like a fingernail which is 2.2 on the Moh Hardness scale.  So if you can scratch your fingernail with the mineral than its harder than 2.2.  If your fingernail scratches the mineral then the mineral is soft and has a hardness less than 2.2.  They compared their minerals to copper (penny), iron (nail) and a steel file.  Once they had completed the data table for each mineral they compared their results to a data table to identify their mineral.  One of the families brought donuts, so once everybody had cleaned up, we feasted on donuts.

We didn’t have time in class but I asked the kids to watch these videos at home.

Big History 014 – Earthquakes

While we watching movies about the layers of the earth last week, I heard one of the students ask, “How do we know that?” Which is a great question because we haven’t dug down to the center of the earth, heck, we haven’t even gotten through the crust yet. So how do we know there is an iron core in the center of the earth surrounded by a molten outer core?  Earthquakes!  Earthquakes generate waves that travel through the earth and we can measure them with seismographs.seismogram  Just like we use radar or sonar to detect things we can not see, we can use waves from earthquakes to learn about the center of the earth.   There are two main types of body waves (waves that travel through the body of the earth), P – waves (primary or push/pull waves) and S-waves (secondary or shear waves).

The P waves travel faster than the S waves so they arrive at the seismograph first.

By looking at the difference in the arrival times of the two types of waves you can determine how far away the epicenter of the quake was from the seismograph.  If you do this for 3 different seismographs you can triangulate the exact location of the epicenter.  This is the lab the kids did this week, I gave them seismograms from three locations for a particular earthquake and they had to measure the arrive times off the data, figure the difference and then use a graph to find the distance from the epicenter.  Then they took a compass and drew a circle of that radius on the map.  Once they had done that for all three locations they could locate the epicenter where the three circles intersected.  Sometimes they get a small triangle instead of a point and that’s ok.  The quality of your end result really depends on your drawing compass, we didn’t  have any locking compasses and it would have made this lab much easier if we had.

We watched the videos above as well as the ones below during class.

 

The lab we did was from a college course I taught many years ago but I found this updated version on the web. I skipped the bit about  magnitude since my students are pretty young and most haven’t heard about logarithms but they did know that an earthquake with  magnitude 7 is 10x worse than a 6, and 100x worse than a 5.

 

 

Big History 013 – Layers

Today was all about layers, layers in the Earth and in the atmosphere.  As the kids arrived they started putting together a lift the flap type thing that showed the structure of the Earth.  The foldable is by Nitty Gritty Science.  IMG_1339

Once everyone was done putting that together we watched Everything You Need to Know about Planet Earth by In a Nutshell – Kurzgesagt.  

We didn’t watch this one in class, but its kind of cute and it would easy enough to make your own earth cake at home.

The Everything You Need to Know About Planet Earth video also talked about they layers in the atmosphere and the  Earth: Power of the Planet  video series by BBC has an entire episode on the atmosphere so we watched the first 20  minutes or so of that on Netflix.  You can find bits and pieces of it on youtube:

The kids then made a model to scale of the layers of the atmosphere in their notebook. I had already cut the paper to size so they just had to glue them in the right order and label each layer.  Like illustrations of the solar system, posters of the layers of the atmosphere are rarely to scale  and show the atmosphere extending out to distances twice as far as the surface of the earth, while in reality its just a very thin layer around our planet.  For the model we made for the notebook, an earth to scale would have filled my living room!  The exosphere extends way past the edge of the book and most of the ‘air’ is in the lowest two layers, the troposphere and stratosphere.  Even in the stratosphere you would need an oxygen tank and protection against the cold and low pressures.

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Big History 011 – Plate Tectonics

I found a good documentary from BBC on Netflix for plate tectonics, so we started class by watching the first 30 minutes of the Volcano episode of Earth: Power of the Planet.  It can also be found on youtube.

I also showed the Alfred Wegener vs The Fixists (Continental Drift)  Science History Rap Battle done by a 6th grade class from San Jose.

And a Minute Earth: Plate Tectonics Explained:

I didn’t show this one in class, but its another nice video on Pangea and plate tectonics.

After the movies the students spent the next hour coloring in a flip book that when finished, shows the continents moving from Pangea to their present day location.  They also cut out the continents to form puzzle pieces and put them together to form Pangea by looking at the fossil evidence and their shapes.  Both of these activities I found online. The flip book can be found on Purdue’s website and is called “Voyage through Time: A Plate Tectonics Flipbook”.  A simpler version of the continent puzzle can be found on the USGS website but searching a little more I found this link, A Plate Tectonic Puzzle – American Museum of Natural History, that is a more complete puzzle. I was a bit worried they would revolt about the coloring the flip book- my hand hurt when I did the whole thing –  but they sat around the table talking about everything under the sun… you know socializing! while they colored.coloring flip book

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