This is the last topic in our unit on heat. I’m going to do a review game that covers topics based on forces from last term and heat from this term in two weeks. I’ve already covered seasons in a previous post. This class was about long term changes in the temperature on Earth.
The first thing I covered was continents moving. About 225 million years ago, all of the continents we know today were joined together into one continent known as Pangaea. The plates separated and continue to separate today. You can see how South America fit into Africa pretty easily. India moved from the East side of Africa all the way up to Asia. When those land masses pushed together they formed the Himalayan Mountains. I went over plate tectonics in my class on geology. This is a good time to go over convection again as well when you discuss the movement of the molten rock in the mantel of the Earth. What is the evidence for Pangaea?
- The fossil record
- Orientation of magnetic molecules in sedimentary and intrusive igneous rocks
- Deposits from glaciers
The same fossils are found spread out in a pattern across today’s current continents. For example the same type of fossils are found in south America and South Africa and no where else. If they were not ever in contact, you wouldn’t expect to find them distributed this way.
The Earth’s magnetic field flips, but at any given time magnetic sedimentary deposits and slowly cooling igneous rocks would have their magnetic molecules lined up with the magnetic field. You can use this information to determine the position of the continents relative to each other.
The Earth goes through cycles when glaciers grow and recede. When a glacier grows it picks up rocks and dirt and very slowly moves them when they are trapped in the ice. As the ice melts and the glacier recedes it drops the dirt and rocks. The same types of dirt and rocks the glacier leaves behind are found on continents that are separated today.
For the activity for this class I had the kids decorate and label the continents from the worksheet above, and then I had them cut them out and glue them into Pangaea. I had a labeled map of Pangaea up on the board for them to follow. This activity is also good for a geography lesson. I showed the kids patterns common in art from different continents like the aboriginal dot paintings from Australia, so they could decorate the continents based on those if they wanted to.
Ice ages are times when the Earth has some ice all year round. We are actually currently in an ice age. However, ice ages alternate between warmer and cooler periods. We are now in an interglacial (warmer) period. The first major cooling of the earth is thought to have occurred when the first organisms to photosynthesize (cyanobacteria) pumped a lot of oxygen into the atmosphere. Oxygen is not a green house gas, so the more of it there is in the air, the cooler the earth is. The current ice age may have been triggered when North and South America connected and changed the ocean currents. Right now the south pole is covered by Antarctica and the north pole is mostly land locked and covered in ice which could be keeping the poles cool. This ice age may also may have been triggered by some tectonic plates colliding and bringing rocks up above the ocean that absorb a lot of carbon from the air when they are exposed to heat and rain. These collisions may also have blocked volcanoes that release carbon into the air. Carbon dioxide is a greenhouse gas. When it is removed from the atmosphere, the Earth cools down.
Within an ice age it is thought that the warmer and cooler periods may be caused by the movement of planet Earth. The tilt of the Earth has a wobble to it. The orbit of the Earth is not a perfect circle and its orbit changes from more circular to more elliptical. These two factors combined correspond to the warmer and cooler times within the current ice age.
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