Blue Dot and Preservation

The Basics of the Blue Dot and Preservation

January 23, 2015

Christopher Smith

        The earth has been in discussion since the beginning of man. Questions of flat or round, does the earth orbit the sun or is the earth the center of the universe, and how did life start? As humans use the finite resources of the earth, many scientists are struggling to find the answer and what effect the inhabitants have on the planet.

The Beginning

        Our solar system is made up of the eight planets, the Sun, dwarf planets, and over a hundred satellites planets. Included in our solar system is also many comets and asteroids. The planets orbits in ellipse formation with the Sun as the center point. Most of the planets travel in an almost perfect circle, except for Mercury. The planets orbit almost on the same plane with plane earth, called the ecliptic. The ecliptic is approximately only seven degrees of incline from the sun’s equator.

 

        According to Arnett (2015) website, All planets “orbit in the same direction (counter-clockwise looking down from above the Sun’s north pole); all but Venus, Uranus and Pluto also rotate in that same sense” (Orbits, para. 1).

        Approximately four and a half billion years ago the earth was born. The Earth rotates counter-clockwise like the sun as the earth also rotates on its axis. The earth takes approximately 24 hours to complete a full cycle. As the earth ages, the rotation has slowed down. Scientist believes the earth has been steadily slowing down ever since its creation. In the early years of Earth, the rotation was faster and caused the earth’s shape to be more of an elliptical. As earth’s age increases, the planet becomes more round. The new form creates issues with the earth’s crust on the planet, forcing the tectonic plates to move, directly changing the surface of mother earth, and its oceans. As the face of the earth’s surface changes, a significant impact on our atmosphere occurs.

        When the earth was young, there was a major collision with another planet causing a direct impact with the earth. The colliding world was destroyed, and almost took the planet earth with it. According to Case Western Reserve University (2006), “The planet was coming in with such force that when it was destroyed, the molten iron in its core continued to travel through Earth, to eventually be included it its core” (Creation, para. 3). The collision theory would also explain the moon’s small iron content. When the explosion from the impact happened, rock and debris were sent out into the galaxy. Over the years, the debris formed the moon. This action also contributed to the moon’s rotation and accounted for the moon’s day as precisely being the same as its year.

Plate Tectonics

         Plate tectonics is a scientific theory of the lithosphere’s motion on the Earth. Today’s popular scientific theory is derived from the concepts of continental drift by Alfred Wegener in the early 20th century and seafloor spreading ideas of the 1960s. According to Merriam-Webster’s Online Dictionary (2015), Plate tectonics is defined as “a theory in geology: the lithosphere of the earth is divided into a small number of plates which float on and travel independently over the mantle and much of the earth’s seismic activity occurs at the boundaries of these plates” (para. 1). As the lithosphere moves, it directly impacts the tectonic plates. The earth’s land masses have shown it was once a single super continent, now broken up into many smaller ones. Mountains rise from the collisions of the plates and volcanoes can emerge as voids between the plates.
Current scientific studies, records and studies Plate tectonics theory. Scientist sees the approach as more of, fact as time continues and details become discovered. A Scientist is careful with this method to not indulge in personal belief, to make sure it is truly fact.

 

        According to Duckeck (2015), “In science, especially if it is a descriptive science which tries to explore nature, it is a good idea to be careful and keep in mind the difference between facts and theories. Still, plate tectonics is the most important theory in geology and – after half a century of scientific research in this field – a very well supported one.” (Plate Tectonics, para. 2).

The Ocean Floor

        The creation of the earth suggests a vast history. Every piece of this planet is part of a puzzle that allows life to survive. Without every piece, earth would be very different, and life on earth may not have been possible. Understanding how earth is formed and why earth is the way it is today will give an understanding how ocean floors are created, and why they are so vital to life on earth.

 

Billions of years ago the Earth emerged from clouds of dust and fire circling the sun. The sun super heated the earth as poisonous gasses were all around. During this time, Earth was under attack by asteroids and comets, and the lands were filled with volcanoes. Earth’s surface was a field of molten rock, and no life was seen. The extreme condition was the new planet for many thousands of years.

 

        With the earth cooling over thousands of years, many layers formed, each with their unique features and needs to sustain life. The internal core of the earth is composed of mainly iron–nickel alloy. The inner core temperature is described as the same as the sun’s surface, approximately 5430 °C. Through Dynamo action of the liquid outer core, the inner core helps the generation of the magnetic pole. The outer core wraps the inner core. Surrounding the outer core is the mantle. The mantle constitutes about 84% of Earth’s volume. There are two parts to the mantle the lower and upper mantle. The lower or inner mantel is the mesosphere. The upper mantle is two separate parts in its self, called the inner Asthenosphere and the lowest part of the lithosphere. The Asthenosphere is approximately 200 kilometers thick, and the lowermost part of the lithosphere is approximately 50 to 120 km thick. Though there has been no direct observation of the upper mantle, the Hawaiian island’s ocean volcanoes do provide samples from eruptions for scientific study. The mantel is mostly peridotite, above this the earth has a layer called the crust. The crust is made up of mostly granite and basalt. The Earth’s crust is occasionally mistaken for tectonic plates.

 

        According to Alden, A. (2015), “The crust is not the same thing as the plates of plate tectonics. Plates are thicker than the crust and consist of the crust and the shallow mantle just beneath it; the combination is stiff and brittle and is called the lithosphere” (Crusts and Plates).

Plate boundaries

        Three types of Tectonic Plate boundaries are present on earth. The first of them would be divergent boundaries. With a divergent boundary, the plates are pulling apart from each other. Rifts or separation when on land will eventually arise; as this happens the area will break apart and fill in with water. Then countries like Iceland currently as one land mass will have many defined land masses. In converging boundaries, the plates collide into each other. In a converging boundary, the crust is destroyed under immense pressure of the collision and recycled back into mantel as one plate is driven under the other plate. Converging boundaries is also what gives shape to mountains and volcanoes throughout earth. On earth, there are three types of converging boundaries, the Oceanic-Continental Convergence, Oceanic-Oceanic Convergence, and Continental-Continental Convergence. Another type of boundary is the Transform-Fault Boundaries, where two plates are sliding horizontally past each other. Each boundary described uses an extreme amount of energy when unleashed causes tremors that change the earth’s surface. Some believe the plates are moving at relatively different speeds and independently of one another. Realistically each of the tectonic plates is moving in a manner, which is interconnected. As one plate moves, the other plates are affected in one way or the other. Many miles away the signs of change can be noticed as each plate must react cohesively with the movement of another plate. Scientist study this in the Atlantic Ocean as the African plate moves away from the South American plate, the seafloor grows larger. Thousands of miles away in the Pacific Ocean, the sea floor area is shrinking as the floor is being consumed in deep trenches.

Natural events: the New Madrid Seismic Zone

        Oceanic floors of today were part of land masses years ago or old oceanic plates of yesterday. The Oceans floors have been through many changes from movement and stress. Today we see an area devastated and at the highest of risk areas known in the United States. Seven hundred and fifty billion years ago during the Neoproterozoic Era there was a supercontinent called the supercontinent Rodinia. During the split up of this region, faults were created. Rock formed from magma pushed up along the rift to the surface. The divergent boundary process changed the face of the earth forever. The effects of billions of years ago are still seen and felt. One such area is called the New Madrid Seismic Zone (NMSZ).

 

        NMSZ is described by New Madrid Seismic Zone (2012), as “made up of reactivated faults that formed when what is now North America began to split or rift apart during the breakup of the supercontinent Rodinia in the Neoproterozoic Era about 750 million years ago” (Geology).

        Deep under the failed rift system is the scars of the split, leaving the area weakened. The rift could have had a profound change to the ocean floors observed today, but another rift started. Approximately 200 million years ago a new rift system called the Reelfoot rift, started. The Reelfoot rift was also a failed rift system formed in the same way as the breakup of the supercontinent Rodinia. Although, both of the rift systems are long gone, the combination of the two rifts left the area weaker than any other area in North America. This area is extremely prone to extensive devastation as the lands change from uplifting and sinking of the area. The sediment, which covers the old rifts system, makes a relatively small quake into a large disaster area as it the earthquake becomes magnified in its effects. Contributing factors of stress to the area came from the last Ice Age. As the ice melted, the lithosphere began mixing with the cold water. The mixing of the lithosphere made ingenious rock sink deeper underneath the fault area. The deep rock may also be melting into a more plastic state as the lithosphere heats the thinner crust allowing more heat to transfer into the already weakened area. The oceanic plate is another contributing for the stress the New Madrid Seismic Zone.
 

        According to the Forte (2007) website “localization arises because of structural variability in the Farallon slab and the low viscosity of the sub-lithospheric upper mantle, and it represents a heretofore unrecognized and possibly significant driving mechanism for the enigmatic intraplate seismicity” (Descent of the ancient Farallon slab drives localized mantle flow below the New Madrid seismic zone).

        The old oceanic plate is driving its self under the North American plate in the Utah region during the break up of Pangaea area.

        According to Nielsen, O.H. (2015), “central part of the Farallon Plate completely subducted under the southwestern part of the North American Plate. Around 23 million years ago, the remnant of the Farallon Plate split into the Juan de Fuca Plate subducting under the northern part of the North American Plate, the Cocos Plate subducting under Central America and the Nazca Plate subducting under the South American Plate” (para. 1).

        The New Madrid Seismic Zone is a unique on earth, where so many traumas from many areas of land and ocean have affected one small place. Billions of years in design, the world waits for The New Madrid Seismic Zone to become a huge sinkhole. Today scientist describes future events in this rejoin would be catastrophic. The great rise and sink of the Ozarks in 1812 is nothing to what could be waiting for mankind in the near future.

Compare and contrast

Continental drift is a theory based on parts of the earth’s crust moves on the earth’s liquid core. This theory is very plausible based on fossil records. Tectonic plates are another theory, which suggests continents move about from one area to another colliding, separating, and rubbing together. This activity creates our ocean floors, mountains, and islands. As void forms, mantel fills the area. As voids close up, plates disappear, and mountains form. Both theories work together like a living puzzle.

Theory example

        As discussed earlier, the African plate moves away from the South American plate placing pressure on the east side of the North American plate through movement. The plate’s movement has caused the ocean floor to become larger. On the other end of the North American plate, the ocean floor is shrinking as an ancient plate disappears under the North American plate. The movement has caused more stress in an already weakened part of the crust in the middle of the North American plate, causing Earthquakes in the Ozarks.

Ending thought

        Our planet is living. Every event, which occurs there is an equal response. The earth is a complex, intricate design. From a magnetic field generator made of use through fluid motion to a crust to protect us from molten lava baths. The Earth has shown the scientist it has been through many changes. The earth’s surface with its lands and ocean floors, though continental drift and tectonic plate movement will always change and what people see today will not be the same thousands of years from now.

The Seawater

        Many people believe water is easy to obtain because most of the world’s surface is comprised of water. The difference between freshwater and seawater is evident, from the salty taste. Most of the water on the earth’s surface is the sea water. As the population grows throughout the world, the need for more fresh drinking water has become hard to obtain.

Chemical and physical properties of water

        Our oceans salt waters change in property according to many variables. Some of these variables include location on the globe; land mass near the area of seawater, the depth of said body of water, and the amount of fresh water introduced to the ocean water. Approximately 96% of the ocean waters on the globe are made up of pure H2O. Nearly four percent of the remaining seawater is made of dissolved compounds. Salts chemical property is NaCl, most of which is found in the marine life in the oceans. The chemical composition of seawater is of as rock erosion and sediments, seafloor, and land volcanic activity, gasses in the atmosphere, organic decomposition of organisms, and the rain. In the oceans sea waters, carbon and marine necessities like nitrogen, phosphorous are also found.

 

        According to Encyclopedia Britannica (2015), “Concentrations of phosphorus and nitrogen are generally low in the photic zone because they are rapidly taken up by marine organisms. The highest concentrations of these nutrients generally are found below 500 meters, a result of the decay of organisms (Physical and chemical properties of seawater)”.
Seawater to fresh water

        Skeletal components of silicon and calcium are also found from the decaying organisms, deep in the oceans waters. The atmosphere affects the life found in the sea. Carbon dioxide from the atmosphere feeds the plant life found in the sea. In direct response to the amount of carbon dioxide intake by marine plants, a release of oxygen is accounted for in the atmosphere. Various toxins are also found in the ocean from dumping of garbage.

        Turning the seawater into fresh water is very costly. Approximately 120 countries in the world make some amount of fresh drinking water for their citizens. Nature can make its fresh water, but as the population continues to grow, so does the demand. A fresh water generator consists of mainly two different types of machinery, a single-stage unit, and a two-stage unit. One popular device to make fresh water is a single-stage generator with the use of a condenser and an evaporator. The single-stage unit is used by many ocean ships to supply fresh water to the crew. During the operation of the generator, water is boiled. As the water is boiling, steam is made. When the steam contacts colder air, the vapor becomes the condensation to form fresh drinking water, and the minerals and salts are left behind. A single-stage generator will use either a heating element or a high-temperature main engine water jacket to help boil the water.

 

        According to Raunekk (2015), “Generally water is boiled at 100 degree Celsius, but in freshwater generator it is done at around 60-70 degree Celsius. For this purpose, educators or air ejectors are use. Eductors reduces the chamber’s pressure to such a point that water starts boiling at a temperature of 60-70 degrees Celsius (Single stage fresh water generator)”.

         With the use of a flow regulator, a person can control the flow of the sea water into the system to help with efficiency or variations of concentration of salt in the sea water. As fresh water is collected in the condenser, it is pumped out and checked with a salinometer to confirm the water is indeed fresh water. A more advanced and efficient manner of the same idea is with a two-stage generator. As hot water enters a pressurized chamber of a two-stage generator, the water would immediately convert into steam. The process is faster than a single stage generator because the need to boil water is gone. By controlling the flow, the pressure and water temperature would lead to a more rapid method of creating fresh drinking water out of seawater.

A greener way to make fresh water is by using a hydrologic cycle. Like a solar panel or solar water heater, the use of sun can make free fresh water. This type of method is not efficient, but for a desperate need or just personal use; it is seen as a viable system. Placing a metal tray filled with water under a transparent panel, and then sealed over a bigger tray, the system is built and ready to go. Place the solar distiller in direct sunlight. As the sun heats the distiller, the water will accumulate on the inner side of the transparent panel. As more water collects, the water will collect on the outer edge and start running down the sides of the bigger pan. The result will leave behind salt deposits in the inner pan and fresh water in the outer larger pan. Solar distillers are growing in popularity in the United States southwest region. According to Donahue (2015), “Solar distillers are also “gaining popularity as a survival tool in Third World countries where fuel is expensive and water treatment options are few (Solar Water Distillation)”.

Ending thought

        The earth’s surface is made up of water. Most of the water is unusable as drinking water to survive on. The process it takes to make fresh water out of the sea water may be easy in thought, but it is time-consuming and fuel consuming. Water is scares in some areas, the process, of making drinking water, is not entirely free, making the situation worse. With a few simple items readily accessible, anyone can make drinking water in an environmentally friendly way.

 

Globalization and Finite

        Many people think the world’s natural resources are never ending. In reality, everything must come to an end, as the saying goes. When concerning natural resources, the statement is all so true. Politicians throughout the world are arguing if the earth’s natural resources will end or is it a myth. Despite years of research saying, the resources will end. Some people religiously believe the scientific data is wrong and will not end.

Finite resources

        The earth is full of finite resources to help sustain the earth and the life on it.

 

        According to Agriculture and Consumer Protection (2015), Water is a finite resource: there are 1400 million cubic kilometers on earth, circulating through the hydrological cycle. Nearly all of this is salt water and most of the rest is frozen or underground. Only one-hundredth of 1 % of the world’s water is readily available for human use (Where is the water, para. 1).

        Water is everywhere, and though there doesn’t seem to be a genuine end to water. Water is becoming more poisonous. As humans abuse the right to use and abuse water, people are finding through research; all life on earth suffers the abusive behaviors. Humans are demanding more meat, bigger automobiles, and more power to live a comfortable lifestyle. Livestock is the earth’s largest pollutant. The livestock industry not only is the greatest source of methane gas polluting the air supply, but also machines and transportation causes the higher use of petroleum products such as gas, rubber, and plastics. Researchers have found these products in our stream, co2 in the air from unburned gasses, but also in the ever-growing landfills where we bury our wrongdoings. Human life on earth cannot seem to understand if a person likes a clean the inside of their home, why it wouldn’t be important to clean the outdoors. Some people feel the need to discard their waste and garbage into the water. This type of ridiculous behavior pollutes our oceans and underground water sources. Co2 thickens our atmosphere trapping the sun’s rays between our earth and the atmosphere, causing higher temperatures. The higher temperatures cause extinctions on land and in the waters. With larger amounts of decay in earth’s waters, the aquatic life becomes ill from the lack oxygen in the water for the fish to breath. The modern traits of people are to detach their wasteful behavior by throwing out the unused, discarded products into the trash. The trash is just the beginning. Trash sooner or later is transported to a landfill somewhere usually outside the town to be buried and forgotten. As the methane gas of all the products decompose into the air, the chemicals leech into the ground waters commonly used for drinking water.

History of the problem

        The earth was designed to sustain life. Life on earth has exceeded the earth’s capabilities. As the population grows, so does the demand of earth’s resources. In the twentieth century, the population growth spiked up for various reason. In the medical field, technology has made it possible for people to live longer. In the United States during the 1900s there were 17.2 deaths per thousand people annually. During 2005, the rate of deaths in the United States decreased to 8.2 deaths per thousand persons (Pearson Education, Inc., 2015). Birth rates per year also have steadily dropped. In 1910, there were 30.1 births per thousand persons in the United States. Birth rates decreased some until the 1950s with 24.1 births per thousand persons in the United States and continued through the 1960s with similar results. In 2005, the United States saw a steady drop in birth rates at approximately 14.0 per thousand people (Pearson Education, Inc., 2015). At first glance, it seems the population should be going down, but because of modern medicine the young people of the 1920s are still alive. The facts would suggest, every year there, may be less per thousand born, in reality there are more births than deaths and more people, in general, are born.

Current level of concern

        Safe drinking water is becoming scares in some areas. The earth, in general, is starting to see a significant problem with safe drinking water to be consumed. Krantz, D., Kifferstein, B. (2010), estimates suggest that nearly 1.5 billion people lack safe drinking water and that at least 5 million deaths per year can be attributed to waterborne diseases (Global water pollution, para. 1). Worldwide beaches are closed for long and short periods because of bacteria’s and diseases. Pollution causes many bacteria to form. Some of these bacteria can make humans and wildlife extremely ill and may kill. The disposal of sewage and livestock sewage is the number one reason and cause of large amounts of bacteria and oxygen depriving algae. Because of human self-centered behavior, earth’s wildlife and marine wildlife both suffer the outcome of greed and inhumane practices.

 

        Jaehnig (2015), A three-year study of 43 subwatersheds within the Lower Kaskaskia River basin has revealed that those in urban areas contain on a day-to-day basis significantly higher levels of both E. coli and phosphorus, a major fertilizer component, than do the largely rural, agricultural subwatersheds (Carbondale, ill., para. 2).

        Within the Lower Kaskaskia River basin, 29 other watersheds in the countryside were also tested. The reports found the watersheds did have lower readings than those in the city, but in no way were they in good shape. Illinois is scrambling to find ways to deal with the issue. A similar case of this in Milwaukee wasn’t considered as early as Illinois problem. In 1993, high Cryptosporidium levels in Milwaukee’s drinking water supply sickened more than 400,000 residents. According to Natural resource defense council (2015), in 1996 the Centers for Disease Control established a link between spontaneous abortions and high nitrate levels in Indiana drinking water wells located close to feedlots (Livestock pollution and public health).

Proposed solutions

        There are many ways to help solve the problem with water pollution and preserving the earth’s finite resource. The easy and cheap, but most efficient method of preservation is to contact the local Government. Asking the local government to influence the community’s water supply company in starting an education program to help stop local polluters could save the city from devastating the ecosystem. Dispose of hazardous waste properly; do not dump chemicals into the sewer system, the gutter and roadside drains leads directly to a local lake, stream, or ocean. Watch the local water source for problems and report them to the proper authorities. Find ways to make or purchase non-toxic chemicals as a substitute. Test the well if a private well is used. These are just a few ways a person may help the environment and take charge of developing a clean water source. The next obvious choice is to reduce, reuse and recycle. Reduce the amount of waste created and the amount of meat products consumed. Reuse items for other uses when possible to decrease the need for production. Recycle everything possible. Recycling reduces the need for production, transportation, reduces greenhouse gasses and helps the economy because it is cheaper to make.

 

        Governments around the world are now implementing incentives for free range farms and organic grown farms. These steps help not only lessen the use of chemicals spray on the grounds but also chemicals injected into the animals of commercial livestock. Governments around the world are also intervening with the use of chemicals at nature’s wetlands. According to Grinning Planet (2015), both inland and coastal wetlands act to buffer surges in runoff and to filter pollutants from runoff and flows (Reducing Nutrient and Pesticide Pollution, para. 5). Local governments are taking steps by offering roadside recycle pick-up and installing sewer drains that let people know not to dump because it runs off to their local lake, stream, or ocean.

Effects

        The problem with, not taking these easy steps to help the earth’s waterways, could be catastrophic. More developed countries have the technology to take the environmental crisis cures much farther with green energy technologies such as wind power, solar power, and wave power. All of these techniques are already in use in the United States and Great Brittan. Countries of less development have less opportunity to developing such technologies. Countries that take the initiative to do all the steps and explore such techniques help not only their country, but also the effects are noticed around the world. If nobody were to join in aquatic sustainability, wildlife would die off, ending the food chain. Citizens in developing countries could perish if fishing was needed for survival. Developing countries could also help the situation themselves by just doing the easy steps. Most of the steps are easily obtained and free. The initiative to maintain our environment would help out the local waterways and provide more drinking water.

Conclusion

        No matter where a person is in the world, everyone on this planet has a hand in how every person lives. The environment doesn’t see greed, race or has favorites. If it is important to live a life to the fullest and longest, then everyone has to join in and take responsibility for what he or she does to the planets water sources. No matter if a person is in a developing country or developed country, there is many ways a person can help the environment. Living proactive toward the environment will only support the cause while attracting more people to get involved.

References

Arnett, B. (2015). An overview of the Solar system. Nine Planets.org. Retrieved January 23, 2015, from http://www.nineplanets.org/overview.html
Agriculture and Consumer Protection. (2015). Water: a finite resource. Retrieved January 22, 2015, from http://www.fao.org/docrep/u8480e/U8480E0c.htm
BBC. (2015). The geology of yellowstone park. Retrieved January 22, 2015, from http://www.bbc.co.uk/dna/h2g2/A3740474
Case Western Reserve University. (2006). Earth’s moon. Retrieved January 22, 2015, from http://burro.astr.cwru.edu/stu/earth_moon.html
Donahue, C. (2015). Water distillation methods. Retrieved January 23, 2015, from http://www.ehow.com/list_6467735_water-distillation-methods.html
Nielsen, O.H. (2015). Farallon plates. Retrieved. January 23, 2015, from http://whatonearth.olehnielsen.dk/plates/farallon.asp
Forte, A. M., Mitrovica J. X., Moucha R., Simmons N. A, and Grand S. P. (2007). Geophysical research letters. Retrieved January 23, 2015, from http://gizmo.geotop.uqam.ca//forteA/Forte_et_al_GRL_2007.pdf
Grinning Planet. (2015). Water pollution solutions. Retrieved January 23, 2015, from http://www.grinningplanet.com/2008/01-08/water-pollution-solutions-article.htm
Pearson Education, Inc. (2015). Births. Retrieved January 23, 2015, from http://www.infoplease.com/ipa/A0922289.html
Pearson Education, Inc. (2015). Mortality. Retrieved January 23, 2015, from http://www.infoplease.com/ipa/A0005131.html
Jaehnig, K.C. (2015). Urbanization affecting water quality in Metro East. Carmi Times.com. Retrieved January 22, 2015, from http://www.carmitimes.com/article/20100920/NEWS/309209913
Krantz, D., Kifferstein, B. (2010). Water pollution and society. University of michigan. Retrieved April 8, 2010, from http://www.umich.edu/~gs265/society/waterpollution.htm
Encyclopedia Britannica. (2015). Marine ecosystem. Retrieved January 23, 2015, from http://www.britannica.com/EBchecked/topic/365256/marine-ecosystem/70718/Physical-and-chemical-properties-of-seawater
Natural resource defense council. (2015). Facts about pollution from livestock farms. Retrieved January 23, 2015, from http://www.nrdc.org/water/pollution/ffarms.asp
New Madrid Seismic Zone. (2012). Retrieved April 7, 2012, from http://www.associatepublisher.com/e/n/ne/new_madrid_seismic_zone.htm
Raunekk,. (2015). Generating drinking water on ship – The Magic Machine. January 21, 2015, from http://www.brighthub.com/engineering/marine/articles/29189.aspx
Alden, A. (2015). The earth’s crust. Retrieved January 23, 2015, from http://geology.about.com/od/platetectonics/a/thecrust.htm

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