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ODU / Atmosphere Sciences / OEAS 106 / How are Earth’s Ocean’s unique?

How are Earth’s Ocean’s unique?

How are Earth’s Ocean’s unique?

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School: Old Dominion University
Department: Atmosphere Sciences
Course: Introducation to Oceanography
Professor: Shannon wells
Term: Spring 2015
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Cost: 25
Name: Oceanography chapter 1 notes
Description: These are notes for the first oceanography test
Uploaded: 03/05/2017
14 Pages 156 Views 1 Unlocks
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Why was there such an increase in ocean exploration during Europe’s Age of Discovery?




∙ How Many Oceans Exist on Earth?




∙ How are Earth’s Ocean’s unique?



Oceanography Ch. 1 Notes 1.1 ∙ 70.8% of earth’s surface is covered by oceans. The oceans comprise  the planet’s largest habitat and contains 97.2% of all the water on or  near Earth’s surface. ∙ How are Earth’s Ocean’s unique? o In all of the planets and moons in our solar system, Earth is the  only one that hIf you want to learn more check out which of the following would be the lsrl for the given data?
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as Oceans of liquid water on its surface. The fact  that our planets has so much water and in liquid form makes it  unique in the solar system. ∙ Oceans are essential to all life form and are in large part responsible  for the development of life on earth, providing a stable environment in  which life could evolve over billions of years ∙ They contain the greatest numbers of living things (ranging from  microscopic bacteria, algae, to the largest life form alive, the blue  whale) ∙ The oceans influence climate and weather through an intricate patter  of currents and heating/cooling mechanisms.  ∙ They are the “lungs” of the ocean, taking carbon dioxide gas out of the atmosphere and replacing it with oxygen gas. They supply at least 70% of the oxygen we breathe. ∙ Oceans determine where our continents end, and have shaped political boundaries ∙ How Many Oceans Exist on Earth? o 1, the oceans are interconnected and form a single continuous  body of seawater, it is also known as “World Ocean” ∙ Four primary/principle oceans plus 1: o The Pacific Ocean- World’s largest and deepest ocean; covers  half of the oceans surface area. (Paci=peace), comprises about  half of all oceans. o Arctic Ocean- the smallest and shallowest ocean o Atlantic Ocean- is the second largest ocean; separates the Old  World (Europe, Asia, and Africa) from the New World (North and  South America), names after Atlas, one of the titans in Greek  mythology. o India Ocean- exists mostly in the southern hemisphere, south of  the equator ∙ Southern Ocean- surround Antarctica, its boundary is defined by the  Antarctic Convergence.  ∙ 97% of liquid water in the world is salt water, the rest of freshwater  (liquid) Ocean vs SeaSea ∙ smaller and shallower than an ocean ∙ Composed of salt water ∙ Somewhat enclosed by land, however some seas like the Sargasso Sea in the Atlantic Ocean, are defined by strong ocean currents rather than  by land. ∙ Directly connected to the world ocean. The Seven Seas 1. The Red Sea 2. The Mediterranean Sea 3. The Persian Gulf 4. The Black Sea 5. The Adriatic Sea 6. The Caspian Sea 7. The Indian Ocean (notice how “ocean” and “sea” are used  interchangeably) 1.2 Early history Exploration ∙ Viewed the ocean as a source of food/fishing ground. ∙ Provided and inexpensive and efficient wat to move large and heavy  objects, facilitating trade and interaction between cultures. Pacific Navigators ∙ No evidence that people evolved on these islands ∙ Required travel by boats (double canoes, outrigger canoes, or balsa  rafts) ∙ Micronesia, Melanasia, and Polynesia cover the largest areas of the  Pacific Island. Earliers Settles Knew where they were because of: ∙ The sun and moon ∙ The nighttime stars ∙ Behaviors of marine organisms ∙ Various ocean properties ∙ Ingenious device called a stick chart. Stick charts are like maps that  depict the dominant pattern of ocean waves. Bent wave directions let  them know when they were getting close to an island—even one that  was located beyond the horizon. ∙ Sextant- measures the position of the sun and stars, (sextant=sixth, in  reference to the instruments arc, which is one-sixth of a circle)Latitude- Location on Earth’s surface based on angular distance north or  south of the equator. Equator = 0 degrees; North Pole = 90 degrees north;  South Pole = 90 degrees south. Longitude- Location on Earth’s surface based on angular distance east or  west of the Prime (Greenwich) Meridian (0 degrees longitude). 180 degrees  longitude is the International Date Line; is a function of time. Chronometer (chrono=time, meter=measure)-Determined longitude;  created by cabinet maker John Harrison. ∙ Today, navigating at sea relies on the Global Positioning System  (GPS), which was initiated in the 1970s by the U.S. Department of  Defense. Initially designed for military purposes but now available for a variety of civilian uses, GPS relies on a system of 24 satellites that  send continuous radio signals to the surface. Position is determined by  very accurate measurement of the time of travel of radio signals from  at least four of the satellites to receivers on board a ship (or on land).  Thus, a vessel can determine its exact latitude and longitude to within  a few meters European Navigators Phoenicians- The first Mediterranean people known to have developed the  art of navigation who lived at the eastern end of the Mediterranean Sea, in  the present-day area of Egypt, Syria, Lebanon, and Israel. As early as 2000  B.C., they investigated the Mediterranean Sea, the Red Sea, and the Indian  Ocean. The first recorded circumnavigation of Africa, in 590 B.C., was made  by the Phoenicians. Pytheas -The Greek astronomer-geographer sailed northward in 325 B.C.  using a simple yet elegant method for determining latitude (one’s position  north or south) in the Northern Hemisphere. His method involved measuring  the angle between an observer’s line of sight to the North Star and line of  sight to the northern horizon. However, it was still impossible to accurately  determine longitude (one’s position east or west). Library of Alexandria- Built by alexander the great, house a collection of  written knowledge that attracted scientist, poets, philosophers, and writers  who studies and researched there, it soon became the intellectual capital of  the world, featuring history’s greater accumulation of anciet writings; all of  its content were burned in 415 A.D. The achievements of the Phonecians,  Greeks and Romans were mostly lost, except the knowledge that the Arabs  retained.  The Middle Ages∙ The Vikings of Scandinavia had excellent ships and good navigational  skills in which they actively explored the Atlantic Ocean. In 1981 the  Vikings colonized Iceland. Erik the Red discovered Greenland. Bjarni  Herjolfsson discovered Newfoundland/Vinland.  ∙ Climate cooling and inappropriate farming practices fro the region  caused these Viking colonies in Greenland and Vinland to struggle and  die out by 1450. The Age of Discovery in Europe (1492-1522) ∙ The 30yr period from 1492-1522 = Europe’s Age of Discovery.  ∙ Europeans explored the continents of North and South America, and  the globe was circumnavigated for the first time.  ∙ Europeans learned the true extent of the world’s oceans and that  human population existed elsewhere on newly “discovered” continents and islands with cultures vastly different from those familiar to  European voyagers.  Why was there such an increase in ocean exploration during Europe’s Age of  Discovery? ∙ Because Sultan Muhammed captured Constantinople which isolated  the Mediterranean port cities from the riches on India, Asia and the  East Indies, causing the Western world to search for new eastern trade  routes by sea. ∙ The Portuguese, under Prince Henry the Navigator led an effort to  explore outside Europe. And established a marine institution at Sagres  to improve their sailing skills. Bartholomeu Diaz and Vasco Da Gama  established a new eastern trade route to Asia. ∙ Meanwhile, the Italian navigator and explorer Christopher Columbus  was financed by Spanish monarchs to find a new route to the East  Indies across the Atlantic Ocean. During his first voyage in 1492, he  sailed west from Spain and made landfall after a two-month journey,  landing in uncharted territory of the Caribbean.  ∙ Columbus discovered North America, however, he never stepped foot  on the soil.  ∙ Age of Discovery was a remarkable circumnavigation of the globe  initiated by Ferdinand Magelian (sailed down the eastern coast of  South America through a passage to the Pacific Ocean.) ∙ English defeated the Spanish Armada in 1588, making English the  dominant world power up until the 20th century. Beginning Voyage for Science ∙ Captain James Cook (1728-1779)- English navigator and prolific  explorer; undertook 3 voyages, the Endeavour, Resolution, and  Adventure between 1768-1779. Mapped South Georgia, South Sandwich, and Hawaiian Islands; killed by the Hawaiians. HE  determined the outline of the Pacific Ocean and using the Chronometer he was able to create the first accurate map of Earth’s surface. He was  also the 1st to cross the Antarctic Circle in search for Antarctica. Cook  initiated systematic sampling of subsurface water temperatures,  measuring winds and currents, taking soundings, and collecting data  on coral reefs. Cook also discovered that a shipboard diet containing  the German staple sauerkraut prevented his crew from contracting  scurvy. NOAA (pronounced “NO-ah”) stands for National Oceanic and Atmospheric  Administration and is the branch of the U.S. Department of Commerce that  oversees oceanographic research. Today’s Exploration: oceanographers employ many high-technology tools, such as state-of-the-art research vessels that routinely use sonar to map the sea floor, remotely  operated data collection devices, drifting buoys, robotics, sea floor  observation networks, sophisticated computer models, and Earth-orbiting  satellites. 1.3 What is Oceanography? Oceanography - Oceanography (ocean = the marine environment, graphy = description of) is literally the description of the marine environment. It is  the scientific study of all aspects of the marine environment. Hence, the field of study called oceanography could (and maybe should) be called  oceanology (ocean = the marine environment, ology = the study of). It is  also referred to as marine science and includes the study of the water of the  ocean, the life within it, and the (not so) solid Earth beneath it. A broad range of interdisciplinary science topics from the diverse fields of geology,  chemistry, physics, and biology are included in the study of  oceanography. Since prehistoric time, people have used the oceans as a means of  transportation and as a source of food. Ocean processes, on the other hand,  have been studied using technology only since the 1930s, beginning with the search for offshore petroleum and then expanding greatly during World War II with the emphasis on ocean warfare. Oceanography is traditionally divided into different academic disciplines or  subfields of study: 1. Geological oceanography, which is the study of the structure of the sea floor and how the sea floor has changed through time; the creation of sea floor features; and the history of sediments deposited on it 2. Chemical oceanography, which is the study of the chemical  composition and properties of seawater, how to extract certain  chemicals from seawater, and the effects of pollutants 3. Physical oceanography, which is the study of waves, tides, and  currents; the ocean atmosphere relationship that influences weather  and climate; and the transmission of light and sound in the oceans 4. Biological oceanography, which is the study of the various oceanic  life-forms and their relationships to one another, their adaptations to  the marine environment, and developing sustainable methods of  harvesting seafood Other disciplines include ocean engineering, marine archaeology, and marine policy. 1.4 What is the Nature of Scientific Inquiry? The overall goal of science is to discover underlying patterns in the natural  world and then to use this knowledge to make predictions about what should or should not be expected to happen given a certain set of circumstances.  his work is based on an assumption that all natural phenomena are controlled by understandable physical processes and the same physical processes operating today have been operating  throughout time. Scientific inquiry is formalized into what is –observations called the scientific  method.  Scientific Method- The principles and empirical processes of discovery and  demonstration considered characteristic of or necessary for scientific  investigation, generally involving the observation of phenomena, the  formulation of a hypothesis concerning the phenomena, experimentation to  demonstrate the truth or falseness of the hypothesis, and a conclusion that  validates or modifies the hypothesis. is used to formulate scientific theories  and separate science from pseudoscience, fact from fiction. The Scientific Method Observation- The scientific method begins with observations, which are  occurrences we can measure with our senses. They are things we can  manipulate, see, touch, hear, taste, or smell, often by experimenting with  them directly or by things we can manipulate, see, touch, hear, taste, or  smell, often by experimenting with them directly or by using sophisticated  tools (such as a microscope or telescope) to sense them. If an observation is repeatedly confirmed—then it can be called a scientific fact. Hypothesis- An attempt to sort out the observations in a way that reveals  some underlying order or pattern in the observations or phenomena. This  sorting process—which involves a lot of trial and error—is how hypotheses  (hypo = under, thesis = an arranging) are made. A hypothesis is sometimes  labeled as an informed or educated guess, but it is more than that. A  hypothesis is a tentative, testable statement about the general nature of  reconsidered and modified observed. In other words, a hypothesis is an initial idea of how or why things happen in nature. a tentative, testable statement  (IT MUST BE TESTABLE). Hypotheses are used to understand certain  occurrences that lead to further research and the refinement of those  hypotheses. Testing- Analyizing and assessing your hypothesis through experimentation. Only after much testing and experimentation—usually done by many  experimenters using a wide variety of repeatable tests—does a hypothesis  gain validity where it can be advanced to the next step. Theory- If a hypothesis has been strengthened by additional observations  and if it is successful in explaining additional phenomena, then it can be  advanced to what is called a theory (theoria = a looking at). A theory is a  well substantiated, well supported and documented explanation of some  aspect of the natural world that can incorporate facts, laws (descriptive  generalizations about the behavior of an aspect of the natural world), logical  inferences, and tested hypotheses. A theory is not a guess or a hunch.  Rather, it is an understanding that develops from extensive observation,  experimentation, and creative reflection. Theories also have predictive value, that is, they are useful in predicting what should happen given a certain set of circumstances. *Theories are the endpoints in science and do not turn into facts through  accumulation of evidence. If a theory is proven again and again, does it become a law? No, a  theory never becomes a law, they are two separate things.  Does science ever arrive at the undisputed “truth”? No, Science  never reaches an absolute truth because we can never be certain that we  have all the observations, especially considering that new technology will be  available in the future to examine phenomena in different ways. New  observations are always possible, so the nature of scientific truth is subject  to change. Therefore, it is more accurate to say that science arrives at that  which is probably true, based on the available observations.*The statements of science should never be accepted as the “final truth.” Heliocentric (helios = sun, centric = center) theory of our solar system  states that Earth revolves around the Sun rather than vice versa. Peer Review Process-, a key component of verifying scientific ideas. Once  scientists make a discovery, their aim is to get the word out to the scientific community about  their results. This is typically done via a published paper, but a draft of the  manuscript is first checked by other experts to see if the work has been  conducted according to scientific standards and the conclusions are valid.  Normally, corrections are suggested and the paper is revised before it is  published. This process is a strength of the scientific community and helps  weed out inaccurate or poorly formed ideas. 1.5 How were earth and solar system formed?  ∙ Earth is the third of eight major planets in our solar system that  revolve around the Sun (Figure 1.17 ). Evidence suggests that the Sun  and the rest of the solar system formed about 5 billion years ago from  a huge cloud of gas and space dust called a nebula (nebula = a  cloud). Astronomers base this hypothesis on the orderly nature of our  solar system and the consistent age of meteorites (pieces of the early  solar system). ∙ Pluto, which used to be considered the ninth planet in our solar  system, was reclassified by the international Astronomical Union as a  “dwarf planet” in 2006, along with other similar bodies. Solar System- The Sun and the celestial bodies, asteroids, planets, and  comets that orbit around it. Nebula- A diffuse mass of interstellar dust and/or gas. Nebular Hypothesis- A model that describes the formation of the solar  system by contraction of a nebula… According to the nebular hypothesis  (Figure 1.19 ), all bodies in the solar system formed from an enormous cloud  composed mostly of hydrogen and helium, with only a small percentage of  heavip elements. As this huge accumulation of gas and dust revolved around its center, it began to contract under its own gravity, becoming hotter and  denser, eventually forming the Sun……(the nebula contracts due to gravity,  as it contracts, the clouds flatten and forms a spinning disk. The disks mas is  concentrated in the center, where the sun is then formed, and planets form  throughout the disk. The accretion of planets: Collision between bodies cause planets to grow larger, and the swirling eddies in the disk accumulate  material, aiding planet formation. In time Orbits are cleared of gas and small bodies, completing the formation of the planets and their moons. ) The material in these eddies was the beginning of the protoplanets (proto = original, planetes = wanderer) and their orbiting satellites, which later  consolidated into the present planets and their moons. Proto Earth Proto-Earth- The young, early developing Earth. Its size was larger than today’s Earth, and there were neither oceans nor any life on the planet. In addition, the structure of the deep proto-Earth is  thought to have been homogenous (homo = alike, genous = producing),  which means that it had a uniform composition throughout. The structure of  proto-Earth changed, however, as its heavier constituents sank toward the  center to form a heavy core. It is theorized that a mars-sized planet named  Theia, crashed into proto-earth creating the ocean and moon from its debris  coalescing into a sphere.  During this early formation of the protoplanets and their satellites, the Sun  condensed into a body so massive and hot that pressure within its core  initiated the process of thermonuclear fusion (thermo = hot, nucleos = a  little nut; fusus = melted). Thermonuclear fusion occurs when temperatures  reach tens of millions of degrees and hydrogen atoms (a = not, tomos = cut)  combine to form helium atoms, releasing enormous amounts of energy. Not  only does the Sun emit light, it also emits ionized (electrically charged)  particles that make up the solar wind. During the early stages of formation of the solar system, this solar wind blew away the nebular gas that remained  from the formation of the planets and their satellites. The protoplanets  closest to the Sun (including Earth) also lost their initial atmospheres (mostly hydrogen and helium), blown away by the bombardment by ionized solar radiation. At the  same time, these rocky protoplanets were gradually cooling, causing them to contract and drastically shrink in size. As the protoplanets continued to  contract, another source of heat was produced deep within their cores from  the spontaneous disintegration of atoms, called radioactivity (radio = ray,  acti = to cause). *Thermonuclear fusion in stars also creates larger and more complex  elements, such as carbon. It is interesting to note that as a result, all matter —even the matter that comprises our bodies—originated as stardust long ago. Thermonuclear fusion- A high temperature process in which hydrogen  atoms are converted to helium atoms, thereby releasing large amounts of  energy.Atom- A unit of matter, the smallest unit of an element, having all the  characteristics of that element and consisting of a dense, central, positively  charged nucleus surrounded by a system of electrons Density and Stratification Density, which is a physical property of matter, is defined as mass per unit volume; how heavy something is for its size. For instance, an object that has a low density is light for its size (like a dry sponge, foam packing, or a  surfboard). Conversely, an object that has a high density is heavy for its size  (like cement, most metals, or a large container full of water). Density is  related to molecular packing, with higher packing of molecules into a certain  space resulting in higher density. For example, the density of Earth’s layers  dramatically affects their locations within Earth, the density of air masses  affects their positions in the atmosphere and other properties, and the  density of water masses determines how deep in the ocean they are found  and how they move (Chapter 7 ). Density- The mass per unit volume of a substance. Usually expressed as  grams per cubic centimeter (g/cm ) For ocean water with a salinity of 35‰  at 0°C, the density is g/cm . * Water has a density of 1.0 grams per cubic centimeter. Density Stratification/Earth’s Internal Structure  Once Earth became a ball of hot liquid rock, the elements were able to  segregate according to their densities in a process called density  stratification (strati = a layer, fication = making), which occurs because of  gravitational separation. The highest-density materials (primarily iron and  nickel) concentrated in the core, whereas progressively lower-density  components (primarily rocky material) formed concentric spheres around the core. Earth became a layered sphere based on density, with the highest density material found near the center of Earth and the lowest-density  material located near the surface. Density Stratification- A layering based on density, where the highest  density material occupies the lowest space. Chemical Composition Versus Physical Properties chemical composition (the chemical makeup of Earth materials). Based on  chemical composition, the earth consists of three layers: the crust, the  mantle, and the core. ∙ Crust- The uppermost outer layer of Earth’s structure that is  composed of basaltic oceanic crust and granitic continental crust. It extends from the surface to an average depth of about 30 kilometers  (20 miles). The crust is composed of relatively low-density rock,  consisting mostly of various silicate minerals (common rock-forming  minerals with silicon and oxygen). There are two types of crust— oceanic and continental. The average thickness of the crust ranges  from 8 kilometers (5 miles) beneath the ocean to 35 kilometers (22  miles) beneath the continents. It is a hard covering or surface layer of  hydrogenous sediment. ∙ Mantle- The zone between the core and crust of Earth; rich in  ferromagnesian minerals. It occupies the largest volume of the three  layers and extends to a depth of about 2885 kilometers (1800 miles).  The mantle is composed of relatively high-density iron and magnesium  silicate rock. ∙ Core- The deep, central layer of Earth that lies beneath the mantle,  composed primarily of iron and nickel. It is subdivided into a liquid  outer core 2270 kilometers (1410 miles) thick and a solid inner core  with a radius of 1216 kilometers (756 miles). It forms a large mass  from 2885 kilometers (1800 miles) to the center of Earth at 6371  kilometers (3960 miles). The core is composed of even higher-density  metal. physical properties (how the rocks respond to increased temperature and  pressure at depth). Based on physical properties, Earth is composed of five layers: the inner  core, the outer core, the mesosphere (mesos = middle, sphere = ball),  the asthenosphere (asthenos = weak, sphere = ball), and the lithosphere (lithos = rock, sphere = ball). 1. Inner core- Rigid and does not flow. The increased pressure at the  center of the Earth keeps the inner core from flowing. 2. Outer core- liquid and capable of flowing. 3. Mesosphere- The middle region of Earth below the asthenosphere  and above the core. The mesosphere extends to a depth of about 2885 kilometers (1800 miles), which corresponds to the middle and lower  mantle. The mesosphere is rigid because of the increased pressure at  these depths. 4. Asthenosphere- Is a relatively hot, plastic (plasticus = molded),  meaning that it will flow when a gradual force is applied to it located  beneath the lithosphere. It extends from about 100 kilometers (62  miles) to 700 kilometers (430 miles) below the surface, which is the  base of the upper mantle. At these depths, it is hot enough to partially  melt portions of most rocks. 5. Lithosphere- Earth’s cool, rigid, outermost layer that includes all the  crust plus the topmost portion of the mantle. It extends from the  surface to an average depth of about 100 kilometers (62 miles). The  lithosphere is brittle (brytten = to shatter), meaning that it will fracturewhen force is applied to it. the plates involved in plate tectonic motion  are the plates of the lithosphere. Viscosity- A property of a substance to offer resistance to flow caused by  internal friction; a measure of a substance’s resistance to flow. A substance’s viscosity often changes with temperature. The internal structure of Earth is determined by analyzing earthquakes that  send vibrations through the deep interior of our planet. These vibrations are  called seismic waves, which allows scientists to determine the structure  and properties of the deep earth and how it changes over time.  *Basalt originates as molten magma beneath Earth’s crust (typically from the mantle), some of which comes to the surface during underwater sea floor  eruptions. Most granite originates beneath the surface as molten magma  that cools and hardens within Earth’s crust. No matter which type of crust is  at the surface, it is all part of the lithosphere. Isostatic Adjustment Isostasy- A condition of equilibrium, comparable to buoyancy, by which  Earth’s brittle crust floats on the plastic mantle. Isostatic Adjustment- (iso = equal, stasis = standing)—the vertical  movement of crust—is the result of the buoyancy of Earth’s lithosphere as it  floats on the denser, plastic-like asthenosphere below; The adjustment of  crustal material due to isostasy. isostatic adjustment provides additional  evidence for the movement of Earth’s tectonic plates. Isostatic rebound- The rise/upward movement of crustal material due to  isostasy. Similarly, both continental and oceanic crust float on the denser mantle  beneath. Oceanic crust is denser than continental crust, however, so oceanic crust floats lower in the mantle because of isostatic adjustment. Oceanic  crust is also thin, which creates low areas for the oceans to occupy. Areas  where the continental crust is thickest (such as large mountain ranges on the continents) float higher than continental crust of normal thickness, also because of isostatic adjustment. These mountains are similar to the top of a  floating iceberg—they float high because there is a very thick mass of crustal material beneath them, plunged deeper into the asthenosphere. Thus, tall  mountain ranges on Earth are composed of a great thickness of crustal  material sometimes referred to as a root, that in essence keeps them buoyed up 1.6 How were Earth’s Atmosphere and Oceans Formed? The formation of Earth’s atmosphere is related to the formation of the  oceans; both are a direct result of density stratification. Origin of Earth’s Atmosphere Earth’s initial atmosphere consisted of leftover gases from the nebula, but  those particles were blown out to space by the Sun’s solar wind. After that, a  second atmosphere was most likely expelled from inside Earth by a process  called outgassing . During the period of density stratification, the lowest density material contained within Earth was composed of various gases.  These gases rose to the surface and were expelled to form Earth’s early  atmosphere. The composition of these atmospheric gases are believed to have been  similar to the gases emitted from volcanoes, geysers, and hot springs today: mostly water vapor  (steam), with small amounts of carbon dioxide, hydrogen, and other gases. Origin of Earth’s Oceans Similarly, their origin is linked directly to the origin of the atmosphere.  Because outgassing releases mostly water vapor, this was the primary  source of water on Earth, including supplying the oceans with water. Figure  1.25 shows that as Earth cooled, the water vapor released to the atmosphere during outgassing condensed, fell to Earth, and accumulated in low areas.  Evidence suggests that by at least 4 billion years ago, most of the water  vapor from outgassing had accumulated to form the first permanent oceans  on Earth. However, research suggests that not all water came from inside the Earth, but from comets. However, analysis of passing comets chemical  composition revealed a crucial chemical difference between the hydrogen in  comet ice and that in Earth’s water. The Development of Ocean Salinity It is likely that the oceans have always been salty because wherever water  comes in contact with the rocks of Earth’s crust, some of the minerals  dissolve. This is the source of salts in the oceans, whether from stream runoff or dissolving directly from the sea floor. Today, new minerals are forming on  the sea floor at the same rate as dissolved materials are added. Thus, the salt content of the ocean is in a “steady state,” meaning that it is not  increasing or decreasing. Chloride ion is important because it forms part of  the most common salts in the ocean (for example, sodium chloride,  potassium chloride, and magnesium chloride). Also, chloride ion is produced  by outgassing, like the water vapor that formed the oceans. Currently, there  is no indication that the ratio of water vapor to chloride ion has fluctuated  throughout geologic time, so it can be reasonably concluded that the oceans’ salinity has been relatively constant through time. The relentless rainfall that landed on Earth’s rocky surface dissolved many  elements and compounds and carried them into the newly forming oceans.  Even though Earth’s oceans have existed since early in the formation of the  planet, its chemical composition must have changed. This is because the  high carbon dioxide and sulfur dioxide content in the early atmosphere would have created a very acidic rain, capable of dissolving greater amounts of  minerals in the crust than occurs today. In addition, volcanic gases such as  chlorine became dissolved in the atmosphere. As rain fell and washed to the  ocean, it carried some of these dissolved compounds, which accumulated in  the newly forming oceans. Eventually, a balance between inputs and outputs was reached, producing an ocean with a chemical composition similar to  today’s oceans. Further aspects of the oceans’ salinity are explored in  Chapter 5 , “Water and Seawater.” Note that some of these dissolved components were removed or modified by chemical reactions between ocean water and rocks on the sea floor.

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