Science Tidbits: Types of Rocks

There are three main types of rocks found on the earth: sedimentary, igneous and metamorphic.  The following "tidbit" provides a brief description of each type as well as an introduction to the Mohs Scale of Hardness.

Sedimentary Rocks:  
Sedimentary rocks cover about 75% of the Earth’s land surface but only makes up about 5% of the Earth’s crust in it’s volume.  This type of rock can be divided into three categories including: detrital, chemical or inorganic, and finally organics.

  

                    Detrital rocks are formed from rock particles. ranging in size from boulders to microscopic clay particles. Chemical, or inorganic rocks, are made from particles that can dissolve in water.  Finally, the organic sedimentary rocks are formed from plant remains.  To the right, is an image of sandstone, a detrital sedimentary rock.


Igneous Rocks:  
These rocks form most of the Earth’s crust. There are more than 600 different kinds all formed from cooled magma.  Magma near the surface cools quickly producing rocks with small mineral deposits, or extrusive igneous rocks.  Intrusive igneous rocks are formed when magma takes longer to cool.  Larger mineral deposits are formed due to the extra cooling time.  Basalt and Granite, shown below, illustrate the two different types.

        
   Basalt- an extrusive, igneous rock              Granite- intrusive, igneous rock

Metamorphic Rocks:
This type of rock typically forms when sedimentary, igneous or other metamorphic rocks are exposed to extreme heat and/or pressure.  These extreme factors actually change the chemical composition of the original rock by realigning the crystals within the rock.  Here are some common types of metamorphic rocks:

 
         Quartzite                         Slate                             Phyllite                            Schist


Mohs Scale of Hardness:

The Mohs Scale of Hardness, created in 1812 by the German scientist Freidrich Mohs, is used to compare the hardness of minerals by seeing which minerals can scratch others.  This scale is purely ordinal in that it can only tell you to what degree "harder" or "softer" one mineral is in relation to another.  For example, Corundum is twice as hard as Topaz.  For now, the diamond tops the scale as the hardest known mineral.  

 

Additional Resources:

• FOSSWeb: Castle of Doom
• The Mystery of the Golden Cube
• The Virtual Rock Box
• Interactive Rock Cycle
• Glencoe: Rock Virtual Lab

Exploring Pangaea

Over the past few weeks, we have been exploring plate tectonics and Alfred Wegener's theory of continental drift.  They have been searching for evidence to support his theory of a supercontinent, Pangaea.  As a culminating project, they created a digital poster to showcase their findings.  Below, I have included a summary of their evidence and a collection of resources.

Evidence to Support Pangaea: 

• The mountain ranges of Eastern North America and Western Europe match in terms of similar composition, age and rock.
• The east coast of South America and the west coast of Africa contain Cynognathus fossils.  These land-dwelling animals had small brains and did not have flippers or gills.  The only way they could have travelled would be across land.  At some point, they would have had to live on the same land mass.
• Similarly, the Indian peninsula, the east African coast, and Australia all contain Lystrosaurus and Glossopteris fossils.

Collection of Resources

• Shake, Rattle and Slide
• Pangaea Project
• Extreme Science
• How Stuff Works: Pangaea Video
• Continental Divide Puzzle
• Major Plates of the World Quiz 
• Pangaea Interactive Map Game
• Pangaea, the Comeback
• Windows to the Universe: Sea Floor Spreading
• Slip, Slide, Collide
• Mountain Maker, Earth Shaker

Journey to the Center of the Earth for Lunch

This week we are digging into the earth's interior and learning about the various layers.  To assess what we read yesterday in R.E.A.L. Science Odyssey: Earth and Space, we took a non-traditional approach.  In short, we made a pizza.  From the moment I saw this lab, I knew it would be a hit, not to mention, a yummy lunch!  The kids were curious and our 8yo told me he was so excited about today's science lesson.  At this point, I was excited!

Lesson: The Earth's Interior

Grade Level: K-3

Background Information:  

The earth is comprised of four basic layers: the crust, the mantle, the outer core and the inner core.  The crust is the outer most layer.  This is the layer upon which we live and is made of soil, rock and seabed.  Of the four, this is the thinnest ranging from a thickness of 8km beneath the oceans to 40km beneath the continents. Moving deeper, we have the mantle.  The mantle is a semi-solid layer of rock that flows due to pressure creating slow-moving currents.  This layer is around 2900km thick.  Deeper still, we have the outer and inner core both of which are made mostly of iron.  The outer core is the only liquid layer and is around 2300km in thickness.  The temperature here lies between 4000-5000 degrees Celsius.  It is thought this layer plays a significant role in the earth's magnetic field.  Finally, the inner core is a solid ball of iron with a diameter of 24km.  Although the temperature here is between 5000-7000 degrees Celsius, the inner core remains solid due to the high pressure.

Man has never travelled to the center of the earth and likely never will.  The models we have of the earth's interior are based upon information gathered during earthquakes and other seismic events.  Scientists study the behavior of seismic waves, like p-waves and s-waves, to increase their knowledge and improve their models.  

Vocabulary:

crust, mantle, outer core, inner core, interior,  seismic, p-wave, s-wave

Activity Suggestions:

1. Watch the BrainPOP movie, Earth's Structure, to jump start the unit.
2. Watch the Savage Earth animation.
3. Use Visuwords to explore the meaning of the vocabulary words.
4. Create a wordle highlighting the key facts from this unit.
5. Make an Earth pizza to review the interior structure. Yummy!

Here are the directions for the pizza.

Step 1: Make your own pizza dough or purchase a ready-made crust.

Step 2: Spread pizza sauce over the entire surface.

Step 3: Cover the sauce with a thick layer of mozzarella cheese.  Cover the pizza right up to the edge because this layer will show beyond the other layers.  This represents the mantle.

Step 4: Spread a thin, circular layer of cheddar cheese in the center of the pizza.  This circle should be about twice the diameter of the tomato slice.  It will represent the outer core.

Step 5: Add a slice of tomato in the center of the cheddar cheese layer.  This will serve as the solid, inner core.

Here's a picture of our earth pizza before baking.

We baked our pizza at 425 for 8-10 minutes.  Then, took another picture before digging into the earth!

I give credit to the writers at Pandia Press for coming up with a great, edible science activity!  Our kids loved the lab and were eager to share their knowledge about each layer of the earth's interior.  As usual, I was blown away with what they were able to take in and process.  Next week, we are exploring earthquakes and volcanoes.  They are so excited and looking forward to making things quake and explode.  Should be another week of learning fun!

Online Resources for Exploring the Water Cycle

Check out the many resources for diving into the water cycle!

• Scholastic's Study Jams: The Water Cycle
• USGS Water Cycle Resources
• BBC: The Water Cycle
• MSNucleus: Water Cycle
• Water Cycle Interactive
• Water Cycle Bag Activity
• Teaching the Water Cycle -- Great Lesson!!
• KidZone: The Water Cycle
• Droplet and the Water Cycle Game
• EPA: The Water Cycle Interactive
• NeoK-12: Water Cycle Videos and Games

Experiment: Observing Changes in Density

This lab explores the effects of temperature and saltiness on density. 

Materials:

• lab handout 
• clear, plastic cups and foam cups
• table salt
• red food coloring
• table salt
• hot and cold water
  

Creating an Underwater Waterfall

1. Fill a plastic cup nearly full with cool water.

2. Fill a foam cup half-full with hot water.  Add a pinch of salt.  Add 6 drops of red food coloring.  Stir until the salt dissolves.

3. Place the eyedropper into the hot red water to warm it up.  After a minute, fill the dropper with the water.

4. Hold the dropper so that it lies at a flat angle at the surface of the clear water with the tip just below the surface.  Gently squeeze out a layer of hot red water onto the surface of the clear water.

5. After a short cooling time, the red layer will form little waterfalls that sink through the clear water.

Conclusions:
1. Explain why the red water floats at first.

(The hot, red water floats because it is less dense than the cold water.)

2. Explain why the red water eventually sinks. 

(The red water eventually sinks because heat flows out of the hot water to the cold water until the temperatures are the same.  Then, the higher concentration of salt in the red water becomes the controlling factor.  The high slainity of the red water makes it more dense than the cold water.  As a result, it sinks.)

This activity was based upon material outlined in CPO Earth Science.