(Credit to Mr. Parr – creator of many YouTube Videos for students)
Convection Currents in the Earth
As we were studying Continental Drift, we learned that although Alfred Wegener had a great theory, he was not able to explain HOW the continents moved. About 60 years later geologists started to look at the ocean floor, and they discovered that the ocean had a very long range of mountains which they called the Mid-Ocean Ridge. Scientists also learned more about what was happening in the mantle, and found that the heat of the core was creating Convection Currents n the mantle.
The tectonic plates rest on the asthenosphere, a layer of soft rock. Rock in the asthenosphere and in the rest of the mantle moves from convection.
Convection is energy transfer by movement of a material. Heat causes material to become less dense – it then rises, cools, becomes denser and then sinks, only to repeat again. In a pot of boiling water, the water gets heated at the bottom, rises to the top, cools when it hits the air, and then sinks again, forming a looped current.
Click on the picture to see the animation.
The core of the earth makes the heat. It causes the molten material in the mantle to rise, cool and then sink back to the center, where it gets heated again. Notice how the convection currents in the earth are all around the mantle, heated by the core.
The lithosphere is broken into tectonic plates, and these float on the asthenosphere. As the convection currents flow, the floating plates also move, very slowly, about an inch a year. This is what caused the continents to move! Look closely at the diagram, and then clink on the link below to see the movement.
As you can see by the animation, the convection currents in the mantle make the plates in the lithosphere move. Some of them move together to collide at a CONVERGENT BOUNDARY to form mountains, and some of them move apart at a DIVERGENT BOUNDARY to form cracks in the crust. Magma comes up through these cracks, creating a Mid-Ocean Ridge on the sea floor.
Click on the link below to see how new ocean crust is being made at the Mid-ocean Ridge, and that the new crust is pushing the older crust away. The farther you go from the ridge, the older the crust is. This is one way that scientists can prove that the plates are actually moving!
Click on the picture above to see the animation.
In class we then took notes on the Smartboard to review the convection currents in the mantle, their effect on the plates of the lithosphere, and we had an introduction to DIVERGENT and CONVERGENT boundaries. The plates move because of the convection currents in the asthenosphere (mantle) forcing the plates to flow with the current.
We started the week with a review of the layers of the earth, and used diagrams on the SmartBoard to identify the various layers and their key features. Below are the screen captures of the SmartBoard activity for those of you that missed the class. We also discussed the two type of crust, CONTINENTAL and OCEANIC, and the characteristics of each. Continental crust is much thicker than the oceanic crust, and is made of GRANITE. Ocean crust is thin, much denser, which is why it is lower on the earth’s surface, and is made of BASALT rock.
We then began a discussion of the evidence that geologist Alfred Wegener developed to support the Theory of Continental Drift – that all the continents were at one time connected into one large land mass called Pangaea. We made cut-out maps of Pangaea and then identified where Wegener discovered similar fossils, land formations, (such as mountains) and evidence of climate changes in glacial scratches and areas of coal. We drew them on the SmartBoard diagrams and colored the areas where he found his evidence. Unfortunately, Wegener was not able to convince the scientists of his day that the continents had actually moved! See the diagram below for the three main pieces of evidence that Wegener used to develop his theory.
Why did not scientists believe that the continents had moved?
What was missing from Alfred Wegener’s Theory of Continental Drift?
What was the missing piece?
An animation of the breakup of Pangaea to form the world we know today!
Enjoy this Music video from Mr. Parr,
a Science teacher who loves music!
CRUST in PIECES
To see a video of the changing earth continents and shapes, click here
Earth has several layers. Many geologists believe that as the Earth cooled the heavier, denser materials sank to the center and the lighter materials rose to the top. Because of this, the crust is made of the lightest materials (rock- basalts and granites) and the core consists of heavy metals (nickel and iron).
The Inner Core is a solid sphere of metal, mainly nickel and iron, at Earth’s center. The Outer Core is a layer of molten metal, also mainly nickel and iron that surrounds Earth’s inner core. The Mantle is the layer of rock between Earth’s outer core and crust, in which most rock is hot enough to flow in convection currents. It is also Earth’s thickest layer. The Crust is a thin outer layer of rock above a planet’s mantle, including all dry land and ocean basins. Earth’s continental crust is 40 kilometers thick on average and oceanic crust is 7 kilometers thick on average.
The Lithosphere is the layer of Earth made up of the crust and the rigid rock of the upper mantle, averaging about 40 kilometers thick and broken into tectonic plates. It is cracked, and makes up the Tectonic Plates of the earth’s surface. Tectonic Plates are large, moving pieces into which Earth’s lithosphere is broken and which commonly carries both oceanic and continental crust. Look at the diagram below to see the various layers.
The Asthenosphere is the layer in Earth’s upper mantle and directly under the lithosphere in which rock is soft and weak because it is close to melting. The lithosphere ‘floats’ on the asthenosphere.
Notes we took in class on the SmartBoard!
Click on the picture below to take you to an interactive animation describing
Click on the pics below to look at the animations we used in class.
In class this week we are reviewing maps, and beginning our study of Topographic Maps. Below is a video that demonstrates the activity planned for this week. If you missed the activity, you can view below and see what we did!
Think back to Grade 6, Nature’s Classroom and Silver Bay, New York on Lake George in the Adirondack Mountains.
Mountains are a great way to use and show the use of elevation maps. Think back to your time at Nature’s Classroom and the hikes that you took. Remember the hills?
In class this week we will start to study Maps and their uses.
TOPOGRAPHY shows us the shapes and features of the earth’s surface, and TOPOGRAPHIC MAPS use CONTOUR LINES to represent the changes in elevation. In class you are learning the vocabulary of contour lines, index contours, and contour intervals.
Below is a topographic map of the hiking trails and the elevations around the Nature’s Classroom location.
Click on the map to make it bigger.
Look at the contour lines and then answer the following questions:
1. What is the elevation of Jabez Pond?
2. What is the distance between the Index Contours? Remember, these are the darker lines.
3. How many contour lines are there between the darker Index Contours?
4. Therefore, what is the Contour Interval?
5. Challenge Question: What is the approximate elevation of the top of No 108 Mountain?
This week we begin our studies with a review of the Scientific Method, an organized approach to defining, thinking about and developing a process to explore a problem statement and to conduct a lab investigation. These steps were taught in the earlier grades, and we began our year with a review of the processes…and did an activity called CSI Bourne to understand the difference between Evidence (Data) and a Claim (Conclusion).
You can also look at a clip of MYTHBUSTERS – HOT or COLD BASEBALL to see how the students used the Scientific Method to conduct their experiement on how temperature may affect a baseball.
….we’ll be using this a lot as the school year gets underway!
There are many tools and links on the classroom website that will allow you to always stay in touch with what we are doing, where classroom handouts and notes will be, and dates of important events like projects and tests. In fact, this school year you will also be creating your own websites for your own work!
Even though no one is perfect, we must all try to do our very best in whatever we do. To be your best in Mr. Ruggiero’s class, the two most important things to do are stay focused on your class work and to keep a cooperative attitude with your classmates and teachers at all times.
Click on the link below to take you to the Classroom Overview for the school year. Understanding how our classroom works will help you to always stay focused and keep a cooperative attitude.
Below are videos to serve as an introduction to the Grade 8 Class trip to Washington, D.C. We have a video on the National Air and Space Museum, the National Museum of Natural History, the US Capitol Dome’s 150th Anniversary, and The Three Branches of Government: How They Function.
We have been studying the effects of unequal heating of the Earth’s surface, and the resulting wind patterns these cause. Land that is heated more directly absorbs more of the sun’s heat through radiation. The ground touches the air, and through conduction, heats the air – the air becomes less dense which causes it to rise. This creates an area of lower pressure in the atmosphere. As the air rises, it cools, becomes more dense, and then falls back to the earth, creating an area of higher pressure. The movement of the air creates a convection current.
AIR ALWAYS MOVESFROMAREAS OF HIGH PRESSURE TO AREAS OF LOW PRESSURE.
Moving air is called WIND.
The spinning of the Earth causes the winds to bend to the right as they move across the globe. We call this effect the Coriolis Effect. Global Winds are winds that move across large areas around the globe. There are three major Global Wind Belts – the Trade Winds, the Westerlies and the Easterlies. These wind belts are found in both the Northern and the Southern Hemispheres. There are also areas of calm winds, called the doldrums near the equator, and the Horse Latitudes nearthe 30 degrees latitudes. See the diagrams below.
The same convection currents that cause the Global Winds also affect the atmosphere at the local level, especially at the seacoast. Here on Cape Cod we experience these local winds during the summer. Cape Cod is kept cool, sort of a natural air-conditioning, by the local sea and land breezes. The hot summer sun heats the land on Cape, causing the air to rise (low pressure). Cooler descending air from the water (higher pressure) rushes in to take the place of the rising warm air on land, forming a cooling Sea Breeze. This keeps the Cape comfortable on most summer days. At night, the land cools down much faster, the warmer ocean water heats the air, causing the air over the water to rise. Cooler air from the land moves in to take the place of the rising are, creating a Land Breeze.
Study the diagram below, and then CLICK on it to see the animation!.
Both Global Winds and Local Winds are caused by the unequal heating of the Earth’s surface, creating differences in air temperatures and air pressures.
Air (wind) always moves from HIGH pressure to LOW pressure.