Marine Science Unit 1.docx

UNIT 1 About the Earth You may have heard that the earth’s surface is about 70 percent water, which means there is over twice as much water as there is land covering the globe. In this unit, you will go beneath the surface to learn about how the earth and its oceans were created, how the structure o...

UNIT 1 About the Earth You may have heard that the earth’s surface is about 70 percent water, which means there is over twice as much water as there is land covering the globe. In this unit, you will go beneath the surface to learn about how the earth and its oceans were created, how the structure of the earth impacts everything from the shape of the continents to tsunamis, and how the scientific method is applied to marine science. WHAT WILL YOU LEARN IN THIS UNIT? After studying this unit, you will be able to: Define marine science Describe the development of oceans Explain different movements in plate tectonics and their results Discuss the scientific method Differentiate between a hypothesis and a theory 01 Studying the Ocean Introduction Deep blue ocean with waves. Marine science is all about the ocean. What do you imagine when you think about marine science? Spotless white beaches, clear oceans, and endless scuba diving among coral reefs? Or maybe you’re on a boat, spotting whales? Or climbing rocks to follow the penguins? Marine science, also known as oceanography, is all of these things and more. It is the study of the ocean, its shores and all the life that depends on these places. You might be surprised to learn that marine science also covers other bodies of water, such as lakes and rivers. Almost 3/4 of the earth’s surface is covered in water, so there is a lot to study! The Ocean is a Vast Space If marine science is the study of the ocean, then what is the ocean? By definition, an ocean is a large body of salt water that fills a large depression in the earth’s surface. Technically, seas are oceans as well, but the term sea is generally used to refer to smaller bodies of saltwater. While the oceans cover the majority of the earth’s surface, the hydrosphere—which is the total mass, or weight, of the water found on, under, or above the surface of the planet— only accounts for less than 0.25 percent of the weight of the earth. So while water takes up a lot of the surface, our planet has much more land than water, in spite of the way it looks. The earth as seen from space. The view from space makes it clear that the earth’s surface is mostly water. While 97 percent of Earth’s water is found in the oceans, there is also water under the surface, known as groundwater. If you know anyone who lives in the country and pulls their water from a well, they are depending on groundwater to provide water to their household. There is also a significant amount of freshwater, meaning water without salt, in rivers, lakes, and ponds. Even though there are some large lakes in the world, these bodies of water make up a miniscule percentage of Earth’s water supply. The majority of the freshwater on the planet is actually held in glaciers. These ice masses might not be the first thing that comes to mind when you think about the world’s water supply, but they hold quite a bit of this precious resource. Pie chart comparing the amount of salt water to fresh water on Earth. Salt water makes up 97.5%. Fresh water makes up only 2.5%. The pie showing percentage of fresh water is enlarged to show its constituent parts. The percentage of water locked in glaciers is 68.9%, ground water makes up 30.8% and the water in lakes and rivers is 0.3%. The vast majority of the world’s water is salt water. Forming the Ocean There is a lot of water on the earth’s surface, but how did it get there? In the very beginning, the earth was a fiery ball of hot rock. About 4.6 billion years ago, the planet began to cool down. This drop in temperature caused clouds to form, leading to constant rain for about 20 million years as the water continuously evaporated, formed clouds, and returned to Earth as rain. In the beginning, the rain just evaporated because the surface was too hot; however, over time the surface cooled, allowing the rain to begin to form the oceans. Because the surface of the earth is uneven, the lower points filled with water. Scientists are not entirely sure what happened next. Some believe that this rain covered the entire surface of the earth and then later receded to allow the land we live upon to emerge. Others believe that some rocky surface always remained above the newly formed oceans. Eventually these rocky surfaces began to support life: plants. Later, animals emerged. The rest is history. Although the Earth is no longer the fiery ball it once was, it is still not a perfectly solid and stable rock. As the Earth cooled, the heavier elements sank to the center and the lighter ones floated to the top where they formed the Earth’s crust, which is the outer layer. Of all the layers of the earth, the crust is the thinnest at about 3.5 miles thick. It is not one solid piece, like the shell of an egg. Instead, the crust is made of many uneven pieces called plates. They float on top of a soft layer called mantle, which is divided into the upper and lower mantle. The upper mantle is the consistency of hot asphalt, so it is thicker, more like sludge than liquid. This means that the surface of the earth is not stable. If you live in a region where earthquakes are common, you may have experienced this instability firsthand. When the plates floating on top of the mantle move or shift, earthquakes are the result. Even under the ocean, plates are moving. Because the mantle is rather thick, the movement is slow. However, even a slow shift has the power to shake things up. Unlike the upper mantle, the consistency of the lower mantle is not the same throughout. The sections that are closer to the core, which is very hot, are more liquid than the sections that border the upper mantle. The area closest to the upper mantle is almost solid rock. From a marine scientist’s perspective, the upper mantle is more important because it directly impacts the plates. Illustration of the Earth with a portion removed to show the various layers. From outer to inner the layers are labeled “CRUST”, “UPPER MANTLE”, “LOWER MANTLE”, OUTER CORE”, and INNER CORE”. The earth has several layers. Other layers of the earth include the outer core and the inner core. These layers are made of the densest elements. With temperatures ranging from 4,000 to 9,000 degrees Fahrenheit, the outer core is so hot that the metal elements that compose it, including nickel and iron, are in a liquid state. The inner core is also incredibly hot with temperatures of 9,000 degrees or higher. At those temperatures, the metal elements are too hot to move and just vibrate in place. In addition, the inner core of the Earth also has incredible pressure: 45 million pounds of pressure per square inch. This is another reason the elements have a hard time moving around. Thus the earth is really solid only on the crust, and even then, the solid places can move, so there is a lot to study about how all these systems interact. The four layers of the Earth have distinct physical and chemical properties. 02 Plate Tectonics The wreckage of houses after a tsunami. Damage from the 2011 tsunami in Japan. Although we are usually unaware of it, the surface of the earth, or the lithosphere, is always shifting beneath us. The thin plates of the earth floating on the mantle rub past, slide under, and crash into one another. When these movements are jarring enough, volcanoes erupt, earthquakes rumble, and tsunamis crash over coastlines. On March 11, 2011, an underwater earthquake formed into a tsunami which hit Japan, causing a meltdown at Fukushima Daiichi Nuclear Power Plant, which resulted in radioactive materials leaking into the environment. This tsunami killed approximately 15,900 people, and left another 230,000 without their homes. Part of marine science is studying these aggressive movements in the hopes that scientists could find a trigger warning that could help them predict when natural disasters will occur and save lives in the process. These movements of the plates are called plate tectonics. Let’s take a closer look at how the plates fit together and how their movements affect everything around them. One of the most important developments in plate tectonics is the theory of continental drift. This idea, which was first put forth by a German explorer and metal expert named Alfred Wegener (1880–1930) in 1912, suggested that all of the land on Earth, which we recognize today as the seven continents, was once a single land mass. He called this enormous land mass Pangaea, which means “all land.” A map of the Earth overlaid with an outline of the tectonic plates Under the surface, tectonic plates shape our planet. Earlier scientists had noticed the ways that the shapes of the continents seem to fit together, but Wegener was the first to suggest that it was the spinning of the earth and the centrifugal force it created that pulled the continents apart. Centrifugal force is the energy that pushes a body away from the center while spinning. If you have ever been pulled to the outer edge of the car on a spinning carnival ride, you have experienced centrifugal force firsthand. In that case, the pull acts pretty quickly because the ride is spinning fast. In the case of the earth, the movement is much slower, causing the plates to move over an estimated 200 million years. Even today, the earth is still shifting, so it is unlikely that the continents have reached their final resting place. As long as the mantle is not solid, there is a chance for further movement. Two globes. On the left, the Earth before the continental drift. On the right, the Earth after the continental drift. Here we see the continents before and after continental drift. If we had the power to move the continents as we know them today back into one landmass, we would find that the pieces do not fit perfectly. This is because some of the edges are under water today and are part of the continental shelf, the border between the crust that makes up the land and the crust that makes up the ocean floor. Although both of these crusts are made of plates, the oceanic plates are made of denser material than the continental plates. The plates that contained more of the heavier minerals sank lower and became the ocean floor while those composed of lighter rock became the continents. These different densities also shape how they move. In the millions of years since the continents were together, their shores have been reshaped by shifts in the individual plates. It was not until submarines were developed in the early 20th century that scientists had much opportunity to study the ocean floor. Once they were able to better measure and study it, they discovered that the plates of the ocean were actually spreading apart. When the plates of the ocean floor move, they create gaps. Magma, the molten liquid of the mantle, is pushed out through these cracks. It cools and hardens when it comes in contact with the cold water of the ocean. Underwater volcano in a lake. Volcanoes have also shaped fresh water lakes. The bottom of Yellowstone Lake in Wyoming reflects the effects of lava flows. Two volcanic vents in the lake continue to change the lake today! The magma fills in the space between the plates and pushes them farther apart. This is known as seafloor spreading. As the plates beneath the seafloor get farther apart, they push the landmasses on the earth’s surface as well. These shifts, and the magma that flows, also create ridges on the ocean’s floor. Because the same basic processes form both the continents and seafloor, the bottom of the ocean has ridges and canyons just like the surface of the earth. 03 Plates and Their Boundaries Trench on the ocean floor. Divergent plates create trenches on the ocean floor. Thanks to many improvements in technology, today we can map and measure the plates that make up both the major land features and the ocean floor. The plates are different from man-made boundaries like the states within the United States or the countries in Africa. National and state boundaries are drawn by humans, and there are plenty of examples in history of borders changing. If you have traveled from one state to another, you probably did not notice a significant change in the landscape or elevation of the road. In fact, without a sign letting you know that you are crossing into another state, it is often hard to tell. The borders of plates are a bit different because each of the plates has a physical edge or boundary. Thus, where one begins and ends is not up to the person drawing the map, but the physical shape of the plate. Because the plates are moving, their borders do change. There can also be changes in the space between them. There are three different types of shifts in plate boundaries, and they are as follows: Divergent Convergent Transverse/Transform Divergent These boundaries are formed when plates move away from each other. In some cases, magma will squeeze up in the gap created by the separation and make ridges. If there is no magma under the plates, valleys will form. If the plates are above the ocean, these valleys can fill with water. The Red Sea was created this way. When plates diverged, they left an enormous gap that was ultimately filled with rainwater and became a sea. Under the ocean, these spaces created underwater trenches, ravines, and valleys. Convergent Illustration of convergent plates. Arrows indicate the movement of the plates. When convergent plates come together, something has to give. Just as plates can drift away from each other, they can also move toward each other, creating convergent boundaries. Because there is only so much room for movement among the plates, when plates move apart on one side, they will push other plates together. Often, one will slide above another. This can create ridges, mountain ranges, or volcanoes if continental plates drift. Below the ocean, the older oceanic plate will be heavier and therefore slide beneath the younger plate. This can also create underwater volcanoes. In some cases, convergent plates will create islands as the plates are pushed above the water’s surface. When the underwater volcanoes erupt, the magma is cooled and, over time, can build enough layers to create an island. Transverse/Transform These boundaries occur when plates slide next to each other. Neither necessarily rises or falls, they just move along their mutual edge. This does not create mountains or valleys; however, it is where earthquakes come from. One of the most famous transverse boundaries is the California’s San Andreas Fault. This is the border between the Pacific Plate and the North American plate boundary. As these two plates move past each other, tension builds and is eventually released in the form of an earthquake. Areas with active plates, such as the state of California, can be assured that there will always be more earthquakes because those plates keep moving. The Effects of Plate Tectonics The plates in the ocean can experience the same movement, which will produce an underwater earthquake. The result of this event is a seismic sea wave, also known as a tsunami. The underwater earthquake essentially shakes the ocean and creates a giant wave. Just as a bucket of water will slosh over the edges if you move it suddenly, the shaking of the ocean floor similarly displaces water. Rather than spilling over the edge, like the water in the bucket, these enormous waves will crash into the coastline and destroy everything they encounter. Island nations in the Pacific are particularly vulnerable to tsunamis. Did you know that the island chain we call Hawaii was formed by volcanoes? Island in the middle of the ocean It is easy to see Hawaii’s volcanic past in some of the islands. It’s true. Several underwater volcanoes erupting over millions of years created this tropical paradise. Some islands are formed by a single volcano, whereas others required many to create them. The Big Island has five volcanoes, and Mauna Loa is the largest of the five. Today it is the most active volcano on Earth. Some of the volcanoes are under the ocean’s surface; others, such as Kilauea, still let their lava flow. Unfortunately, scientists cannot yet tell when tsunamis or other natural disasters are going to happen. Even understanding that the plates are moving and how some of the plates move is not enough to predict an earthquake. For instance: Scientists noticed movement in plates bordering Southern California on September 30, 2016, and issued an earthquake warning. However, no earthquake occurred. Evidently the plates could absorb those changes without shaking the surface. Other times, there is no indication that the pressure is building until the plates suddenly shift. If you have ever tried to shove something really heavy and almost lost your balance when it suddenly moved, you know pressure can build up and throw things off balance when it is finally released. Volcanoes are similarly unpredictable. Scientists can tell when they are active, meaning likely to erupt. However, they cannot fully explain hot spots, places where the magma beneath the surface is hotter than the other magma in the area. Science has come a long way in understanding plate tectonics, but there are still many mysteries. Even though it is possible to measure the plates, and in some cases their movement, nature is still full of surprises. 04 Sea Level Change Marine scientists need a working knowledge of the ocean floor and how this shifting landscape interacts with the land around it. Because all life depends on the resources on the surface level of the earth, any change in the crust will impact the environment around it. Not surprisingly, the areas that border the oceans are going to be particularly vulnerable to plate movement. One of the results is sea level change, also known as eustatic change, which is a measurable change in the level of the world’s oceans. These changes are most visible on the coasts, but the oceans are such an important part of the environment that the impact can be global. There are a few different reasons why the volume, or amount, of water in the ocean changes. Movements in the plates of the ocean also impact the water level. For example: Divergent plates create a gap on the ocean floor, and this gap will be filled by ocean water. If the plates are large enough, this shift in the water can lower sea levels. Conversely, the sudden creation of an ocean ridge would displace water and cause ocean levels to rise. Shifts in plates are not the only cause of changes of sea level. One of the biggest factors is icebergs. Remember, almost 69 percent of the world’s fresh water is captured in icebergs. When temperatures increase, icebergs melt, putting more water in the ocean. Similarly, extended periods of cold, such as those that occurred during the Ice Age, increase the size of icebergs. This could actually lower the amount of water in the ocean. Icebergs are formed when a portion of ice breaks off an ice shelf, ice sheet, or a larger iceberg. Icebergs float in the ocean but are made from frozen freshwater. Scientists study icebergs to document the changes in the size of the icebergs and the impact on the oceans. The city of Venice, Italy, has a sea level problem. Scientists estimate that it has been sinking 5 to 10 centimeters (2 to 4 inches) per century. Rising oceans and the fact that the land under Venice is more mud than rock means that flooding is an increasing problem in this famous city of canals. Street canal in Venice With canals for its streets, Venice is greatly impacted by changes in sea level. Warm temperatures do not impact just icebergs. They can also cause the water in the ocean to take up more room, raising sea levels. If you have ever boiled a pot of water on the stove, you have seen water take up more space and maybe even bubble up and spill over the edge of the pot. The ocean certainly does not get this hot, but it can warm enough to expand the water molecules a little. Even a small change in a body of water as vast as the ocean can make a big difference. Like the movement of the plates on the earth’s surface, changes in sea level occur very gradually. There are regular changes, such as tides, which will be discussed in upcoming chapters, but a significant long-term change in sea level takes thousands of years. For instance: Scientists estimate the sea has been at its current level for about 2,500 years. However, changes in the environment could accelerate changes in sea level. This is an issue of great concern for marine scientists. 05 The Scientific Method You have learned a bit about the marine part of marine science, so let’s now turn to the science. Science is defined as the study of the structure and behavior of the physical and natural world using observation and experiment. Like all disciplines, science has its own way of doing things, which is called the scientific method. This means that all scientists, whether they are studying giant whales in the ocean or microparticles in outer space are using the same methods to reach their conclusions. Developed in the 17th century, the scientific method employs the following steps: Questioning Creating a hypothesis Conducting experiments or making observations to prove the hypothesis Reaching a conclusion Let’s explore those steps in a little more detail. Questioning A woman thinking. She is surrounded by question-mark symbols of various sizes. The scientific process begins with a question. Scientists begin with a question. It might be something they want to know, such as “How old is the ocean?” It can also be a problem that needs to be solved, such as “What is the best way to clean up the human trash in the ocean?” The questions represent something that they want to understand better. In science, questions also have answers that can be observed and measured. Abstract questions, such as “What is the meaning of life?” belong to other disciplines, such as philosophy or religion, where people wrangle with ideas. Scientific questions can always be tested and answered with facts. Hypothesis A hypothesis is a scientist’s best guess at an answer to a question. In other words, it is what the scientist initially believes is the correct answer. A hypothesis can be proven right or wrong through observations or experiments. While scientists love it when their hypothesis turns out to be right, they often learn a lot when they do not get the results that they expected. Thus testing a hypothesis creates an opportunity for scientists to learn more about their subject regardless of how the experiment turns out. Experiment An experiment is an activity designed to test an idea. For instance: If you were trying to figure out how much water expands when freezing, you would measure the volume of water in a liquid state, freeze it, then measure it again. Most scientific experiments are far more complex than this, but they all have something in common: they are set up to prove or disprove a hypothesis. Gloved hand pouring a green chemical into a beaker in a laboratory. In the background is a board containing chemical structures Experiments test the validity of hypotheses. Observation Some aspects of science are a little hard to study through experimentation. Think about the plate tectonics you just studied. We really don’t want scientists shifting a plate just to see what will happen next. In a case like this, observation is going to be a far better way to understand how the earth moves. Thanks to sophisticated equipment, scientists can now track and measure the small movements in the plates. This information can be used to form and test hypotheses. In science, observation is not just sitting there watching something happen. It also includes recording every possible detail and thinking about what the information reveals about the object being studied. These are the basic steps of the scientific process. Scientific disciplines often have their own methods of recording or documenting results, but the overall process is the same. When the scientific process is complete, scientists write up the results, and this is the conclusion. It is then shared with others in the field. In many ways, science is like a worldwide conversation among experts, all asking slightly different questions. This enables scientists to learn from each other, accelerating scientific progress. Marine scientists use these tools to collect data and make observations. 06 Scientific Theory and Laws Next Steps in Knowledge Scientific thought does not end when a hypothesis is proven or disproven. A hypothesis that can consistently be proven true can become an explanation for observations, or a theory. Theories relate to laws, which are generalizations about phenomena, and help to explain how laws work. It is important to note that theories and laws are not the same thing and one cannot become the other. According to Dr. Paul Narguizian, professor of Biology and Science Education at California State University, 'laws are generalizations about phenomena while theories are explanations of phenomena.' It is also important to recognize that neither theories nor laws are distinguished by their degree of verification; in science, they are separate ways of discussing, exploring, and explaining phenomena. In science, certain laws are also often known as natural laws. One example of a natural law important to marine science is Archimedes’ law of buoyancy. Archimedes, a Greek mathematician and inventor found that when you put an object in a body of water, there is an upward force that is equal to the weight of the fluid that’s displaced by the object. The story goes that Archimedes discovered this as he got into and out of his tub and observed the water height change. Archimedes’ law helps with the design of ships and submarines, as the engineers can now calculate how deep they want their ships to ride in the water. The story of Archimedes is another reason why it’s important to be continuously observing our environment with a scientific eye! Father and son walking on a floating bridge built across a sea. Will you float or sink? Archimedes discovered the math to answer that for you! Scientists are very happy to find laws because they represent certainty. Of course, there are always limits to science and although it is rare, scientific theories can be disproven, or shown to be false. For instance: Albert Einstein (1879–1955) thought that the universe was static, meaning that it had a defined size. This was an accepted theory until the work of Edwin Hubble (1889–1953)—yes, the same Hubble for whom the orbiting Hubble Space Telescope is named—proved that the universe is actually expanding. Science represents our best understanding at the time. It is almost guaranteed to change and evolve, and undoubtedly some of the information we accept as fact will seem silly to scientists a hundred years from now. At the same time, our era is also providing a valuable foundation for those future scientists’ work. Knowledge Check By answering these questions, you can test your understanding of new information and uncover any gaps in your knowledge. Reviewing the feedback will help you focus your studying before taking the graded unit quiz. Conclusion The story of how the oceans formed is an important part of understanding how they function today. The same patterns of shifting plates and environmental changes that determined the shape of our continents are still slowly changing the earth’s crust above and below the water. Sometimes these changes are big and dramatic, such as an earthquake or volcanic eruption. Other times they are so small that it takes specialized equipment to detect them. Fortunately, scientists today have a lot of information to work with thanks to centuries of the scientific method. This approach ensures that scientists use the same standards to define the facts that shape our understanding of the world.