The Rock Cycle and Sedimentary Rock by Tommy Geiger

Ever wondered how rocks are made? First off, there are three different kinds of rocks, Igneous, Sedimentary, and Metamorphic. Each rock is formed in different ways.

        The word "Igneous" comes from the Latin word ignis, which means "fire". Igneous rock is any rock that is formed from magma or lava, usually from a volcano. When a volcano erupts, it spews hot substance called lava. Magma is molten rock found in the earth's mantle and trapped under the earth's surface. When magma exits the earth's crust, usually through a volcano, it becomes lava. Eventually, this lava will cool and solidify, creating Igneous rock. Igneous rock can also be formed under the earth's crust, when magma from the mantle cools and hardens, turning into rock. When Igneous rock is formed below the earth's crust, it is called intrusive. When it is formed on the earth's surface, it is called extrusive. Sometimes, Igneous rocks may have holes in them from trapped gas as the lava was cooling, such as Pumice and Scoria. Some examples of Igneous rock are Granite, Obsidian, and Basalt.

  
Lava from a volcano cooling and solidifying into Igneous rock.

        Sedimentary rock is rock that is formed by the compaction and cementation of deposited sediment on earths surface, especially on the bottom of oceans and rivers. As the river erodes mountains, it carries lots of different size sediment with it, including large rocks, gravel, sand, and silt. When the river reaches the ocean, most of the larger sediments have already been deposited farther upstream, so the smaller sediments such as sand, silt, and clay, get deposited on the sea floor or in the delta of the river. Overtime, these sediments pile up, compacting each other, and minerals from the water cement them together in the layers that characterize sedimentary rock. Later, if that ocean disappears because of subduction or drifting continents, the mountains of sedimentary rock on the ocean floor gets exposed. We see so much of it today because New York used to be a sea. Sedimentary rocks are evidence of erosion because the sediments that make up the rock come from deposition of eroded sediments from mountains.

    
These cliffs show clear evidence of sedimentary rock and erosion and deposition.

        The last type of rock is Metamorphic. Metamorphic rocks form from heat and pressure deep under the earth's surface. When any kind of rock, including Metamorphic, gets pushed deep under the earth's surface by any force(subduction, drifting continents, earthquakes), they are subject to extreme pressure from all the plates pushing against each other. Also, the closer the rock is to the mantle, the more heat affects it. When rocks are under extreme heat and pressure, the rock may change it's texture, crystal structure, and mineral content. When a rock changes because of these forces, it becomes a Metamorphic rock. Metamorphic rocks are classified by the arrangements of grains that make up the rock - Foliated or Non-Foliated. Some examples of Metamorphic rocks are Marble, Slate, and Gneiss

    
The above Metamorphic rock's layers were created by extreme heat and pressure under the earth's crust.

The Rock Cycle

                                               
This diagram shows how different kinds of rocks can be transformed into one another and what forces cause them to do so.
Click here to better understand the rock cycle!

        Clastic Sedimentary rocks form when a bunch of fragments from other broken rocks get compressed together and cemented. These rock pieces can be large boulders or microscopic particles of clay. First, rock sediments get deposited on the floor of a river or ocean. Then, as more layer accumulate, the pressure of all the layers compacts the sediments. Finally, minerals from the water and the rock seeps into the holes between the sediments and cements it all together, creating Clastic Sedimentary Rock.
        Shale is a type of Clastic rock that forms when clay piles up in thin flat layers. No cementation is needed to hold the particles together, and the holes are too small to let any water through them. Conglomerate, on the other hand, is made of many rounded pebbles and sand cemented together.

    
Shale(left) vs. Conglomerate(right)
     
        Organic Sedimentary rock is made of when the dead organic material piles up in swamps or oceans, and over time, the minerals and buildup of that material turn into organic sedimentary rock. For example, Limestone forms when remains of the hard shells of living animals from a coral reef pile up and compact over the weight of more and more layers. Some of the shells dissolve into calcite, which cements all the layers together to form Limestone. Chalk is a type of Limestone.

  
In this Limestone you can see the remains of tiny shelled creatures.

        Finally, chemical Sedimentary rock is formed when dissolved minerals, in a lake for example, crystallize. When this happens with dissolved calcite it creates chemical Limestone. Chemical Sedimentary rocks can also form when there are mineral deposits in a lake or sea, and the lake evaporates, leaving the minerals to harden and crystallize. Gypsum is an example of a chemical Sedimentary rock formed by evaporation.

    
Rock salt is a chemical Sedimentary rock.        These chemical rock formations are left as this lake evaporates.


Another example of chemical Sedimentary rock.


Thanks for reading my post! - TommY
     

Drifting Continents Story By Lauren McNamara

I have been working on time travelling machines in my basement ever since 6th grade. One day when I was in 8th grade and we were learning about the formation of the continents over millions of years, I knew what I had to do. Something in my brain just clicked, so when I got home, I ran down to my time travelling machine, and attached new wires and fed it more electricity. After a week or so when all the mistakes were fixed, I knew I should test it out. An idea popped straight into my head. What could be better than learning and physically studying the formation of Earth? So, I took off with my dog, Maggie, and went back 500 million years ago.

All of a sudden, my time machine crashed with a loud thud. I went 500 million years back in time! My dog, Maggie, immediately got out and started sniffing the barren land, although there wasn't much to smell. All I saw were rocks. There were no sight of trees, plants, or animals yet on this land, known as Taconic Island Arc (Bronson Hill). The TIA will soon be a part of North America in a few million years, and will be known as Massachusetts, along with other (soon-to-be) states, which will make up New England. The TIA used to be a part of Africa, but then it broke off and is now floating towards North America. Also, another thing about the TIA is that it is covered with volcanoes! Better hop back in my time machine now!

When I reached the TIA once again, except this time I went back 455 million years ago from present day, it has finally collided into North America. I’m starting to see mountains form around me as Maggie runs around the base of them. These mountains will soon become the Berkshire Mountains/Hills. On the western side of the Berkshires, I see a taller mountain, one that is growing to become Mount Greylock, the highest mountain in Massachusetts at an elevation of 3,488 feet. Along side Mount Greylock are clusters of smaller mountains, known today as the Taconic Mountains. Avalon, another plate broke free of the united African-South American continent (South America & Africa) and is heading towards North America, also like the TIA. It holds land that came to be Boston. I better get Maggie and go back in my time machine again!

I reached Avalon, which meant I went back 420 million years ago, after it crashed against North America. It looks like the layers of this land folded up in a up-and-down pattern. Now I am starting to see huge mountains, which are forming in central Massachusetts. These appeared because since these two plate collided against each other, the layers pushed themselves upwards, creating mountains. Anyways, just like the TIA and Avalon, one more plate is approaching. This plate is Africa (the continent). It is approaching as we are shifting north, although we are still under the equator. Maggie searches the seas by gazing in the water, then swimming, looking at the primitive fish, which recently started growing. Another thing that is growing are plants, which are flourishing on the land. I should get back in my time machine before Africa hits!

Crash! My time machine roughly landed on North America again, meaning I went back 280 million years ago. Maggie quickly hopped out of the machine and ran around. I slowly got out, amazed by the look of North America. Africa had collided with it, and I could almost literally walk to Africa from where I was standing (Massachusetts). Also right now, North America has moved closer towards the equator, meaning that its getting hotter. Along with the continents colliding, more mountains are forming, along with old mountains getting taller. Not only did Africa connect with North America, but all the continents did, which meant Pangaea. Pangaea is the stage in which all the continents are formed together. When they are formed together, you can’t see any water from oceans, too. It looked like some plants, animals, and trees, but still not much. Also, dinosaurs will appear shortly. I am getting back in my time machine now before Africa hits!

“Landing” says the screen on my time machine. This time, Maggie and I are both happy that it landed softer than the other times. Anyways, when we got out, it was 190 million years ago from present time. Unlike my last trip to North America where I could walk to Africa, this time it separated out of the eastern coast, causing fractures of the land. There is a gap filled with water in between North America and Africa, which was the beginning of the Atlantic Ocean. As I also look around, I notice dinosaurs crawling everywhere I look. Although it would be scary at sometimes, I knew the early humans would not appear for another 188 years. So, I jumped in my time machine, making sure Maggie would not bother the dinosaurs, or get lost in the huge amount of land.

When we finally got back, I learned so much about Earth’s history of drifting continents and how it came to be like what it is today. I would definitely like to do that again.

Geologic time by Matt L.

Geologic Time

Have you wondered what happened before we arrived on earth?  Earth is about 4.6 billion years old, and humans have only appeared in the last 100,000 years or so.  In the billions of years to form, a lot has happened.  We call that period geologic time because it is the time of the formation of earth.  In other words, geologic time is the time of earth’s development to the present day.  Events that have happened on earth can ordered on a timeline.

In geological time there has been 6 major events:  the formation of the earth and moon 4.6 billion years ago; earliest life 3.9 billion years ago; early land plants about 420 million years ago; largest mass extinction 248 million years ago; dinosaur extinction 65 million years ago; and “Lucy” Early Hominid 4 million years ago.

Source:  http://www.ucmp.berkeley.edu/education/explorations/tours/geotime/gtpage2a.html

You can think of earth’s past as a book.  If you were to write earth’s history and each page represented one year, the book would be 4.6 billion pages long.   This book would be 145 miles thick.  An average person reads about one page every two minutes.  It would take that person 17,503 years to finish the book if they read non stop.


Source  http://www.petrostrategies.org/Learning_Center/exploration.htm

Scientists have figured out events in the earth’s past through the study of rocks.  When fossils are found, geologists can date them by looking at the layers of rocks on earth.  Geologists have figured out that the earth is covered with layers of rocks, with the older rocks on the bottom and the newest at the top.  Basically, this means layers of rocks build on top of one another as time passes.  Geologists refer to this as the Law of Superposition.

Source:  http://lifesciencedaily.com/wp-content/uploads/2011/05/Fossils.jpg

With each layer of rock representing a period of time, scientists looking at the sequence of the layers of rocks can tell the order of when events on earth happened.  Scientist can use all of the sequence of layers to also figure out the relative order of when events happened on earth.  Evidence about the order of events in earth’s history are also found in fossils buried within the rock layers.  This ordering is known as relative time.  
I think that it is pretty awesome that we can figure out what happened billions of years ago when we have lived for about hundred thousand years.

Tides - Sharmila Mysore

             Hey Science buddies!        
                              I remember being at the beach in Cape Cod and in the morning the water was so high above the ground that it nearly touched the road. But then in the afternoon the water seemed to lower a lot, so much that the sandy, beautiful beach had finally shown. Little did I know why this was happening...
                              It was the cause of Daily Tides, they happen twice a day. And there are two types: High Tide and Low Tide. Daily Tides are the glorious rise and fall of water coastlines that are the reason our sand castles at the beach get washed away...
                               Daily Tides are caused by the positioning of the Sun, Earth and Moon. There are two High Tides and two Low Tides a day. The first High Tide is caused by the gravitaional pull of the Moon and Sun. The second High Tide occurs 12 hours later and is caused by Centripital force. Centripital force is when something is being forced to stay put by the force of spinning but wanting to swing away. In this case the Earths is the one spinning and swinging the water (rotating fast) causing the water to want to fling of the Earth creating a tidle bulge. But the Earth's gravity makes it stay put. Low Tide occurs when the Moon and/or Sun is pulling on the opposite side of the Earth causing the other side to stay still. This is because there is no force pulling the water to it, so therefore it has no reason the bulge.

                                                   

                                                                      The cause of High Tide and Low Tides.
                                                                              (curious.astro.cornell.edu) 
                                  
                                        Daily Tides occur at different times each day. Because the Moon is revolving around the Earth as the Earth revolves around the Sun, this causes Daily Tides to delay by 50 minutes each day. The Moon rotates and revolves at a much slower pace than the Earth, therefore it needs more time to catch up (50 minutes, slow poke!)

                                                                                   The Tidal Effects.
                                                                          (science.howstuffworks.com)
                                       
                                        Since Tides are the rise and fall of the Earth's water coastline there are two types of Monthly Tides. Spring Tide and Neap Tide. Spring Tide occurs when the Sun and Moon are lined up on either/opposite sides of the Earths, creating a tidle bulge which combines both the Sun and Moon's gravitational force. This makes the bulge much stronger, therefore there is a greater range between High and Low Tide. At this point the highest high tide and lowest low tide occur. Spring Tides happen only on a Full and New moon phase. There are also Neap Tides each month. Neap Tides happen when the Sun and Moon pull at a right angle, the gravitational pull is towards the Sun and Moon therefore it creates a very calm and still tide on the opposite side. This is when the lowest low tide and highest high tide occur. A Neap Tide happens on the 1st and 3rd quarter moon phase.
                                                      

                                                                                  Spring and Neap Tides.
                                                                                         (dolio.lh.net)
                                       
                                      In class this week we looked at many diagrams and read notes on the tides. We also spent a lesson looking at a globe and used a rubber-band to show the tidle bulge of each tide. Then we had a homework assignment where we had to explain what each tide was and what causes it. To help us with this we looked at the textbook and read the pages on the discription of each tide as well as looking at the diagrams in the textbook. By the end of the assignment I think we really understood the different tides. I know I did!!!

                                                                       Bay of Fundy, High and Low Tides.     
                                                                 (mrnagribianko-ecozones.wikispaces.com)                 

                                                                                    I LOVE SCIENCE!
                                                                                (famousquotesabout.com)
                                                                                                                     Love Always,
                                                                                                                                     Sharmila