Introduction to Ocean Sciences

Chapter 1: The Ocean Planet

Guide to Reading and Learning

Most of us have watched videos of the underwater world that lies beneath the ocean surface and some of us have even been lucky enough to visit a small portion of that world.  The strange looking world of the seafloor and the amazing abundance and variety of ocean life are most likely one of the things that have drawn you to study the oceans.  However, did you know that life as we know, even terrestrial life, could not exist on our planet Earth without the oceans?  Did you know that Earth’s climate is controlled by the oceans?  Did you know that the oceans and ocean resources are essential to modern civilization in many ways that far exceed the value of the fisheries that they sustain?  This book explores these and many other aspects of the oceans that intersect our lives and, by the time you finish reading, you will understand why we call Earth the Ocean Planet. 

This first chapter of our journey through the oceans presents a brief overview of the many ways that the ocean is important to human civilization and our everyday lives.  One connection with our lives is highlighted here and will be revisited many times throughout the text:  Simply stated, global climate change induced by the greenhouse effect is probably the most important challenge ever faced by human civilization. The key to understanding climate change, and its likely effects on us, is to understand the intimate dance of interactions between the oceans and atmosphere. 

There were not always oceans on Earth and there are no oceans on any of the other planets or moons in our solar system.  You will learn briefly what we know about the history of the formation of the Earth and its oceans.  This will reveal to you just how unusual, although probably not unique in the universe, our ocean planet is.  It will also show you just how critical the oceans are to the development of life.

To describe our Earth and its oceans scientists often use many perhaps unfamiliar scientific units and types of graphical presentation, and this text is no exception.  Thus we end this chapter with an explanation of how you should study and interpret information presented in a map, graph or chart, and how you can interpret the scientific notation and units that we use.  We must learn the basic elements of this language of science before we can communicate with each other about Earth and ocean sciences. Learning the basics of this language will ensure that you can understand, more easily learn and, most importantly, enjoy the concepts and information in the book.  Graphics are used extensively in the text to visually represent what is usually communicated by way of mathematical formulae.  A wealth of information is contained in these graphics and you should carefully study each figure in detail.  Many texts use graphics as illustration, but here you will find that the graphics are an integral part of the learning experience.

Chapter 1 Essential to Know 

Critical Concepts used in this chapter

CC.1, CC.5, CC.9, CC.10, CC.11, CC.14

 
1.1 Introduction

  • The oceans and processes that occur in the oceans have had a wide range of importance to humans throughout human history. About half the word’s population lives close to a river estuary or ocean coastline.
  • Human interactions with the oceans have changed the oceans in many ways.

1.2 The Oceans and the Earth’s Environment

  • Human enhancement of the greenhouse effect is perhaps the most important environmental problem in the world today and will likely continue to be so for many years to come. 
  • The enhanced greenhouse effect is driven by releases of carbon dioxide methane and other gases into the atmosphere. The excess carbon dioxide and other greenhouse gases do not block the suns energy, but do block the longer wavelength energy emitted by the Earth to space. In this way the balance between energy input and energy output to the Earth is altered.
  • Interactions between the atmosphere and oceans are complex, but they all affect or control Earth’s climate.  The problem of global climate change is, therefore, one of the most important driving forces behind much of contemporary ocean research.

1.3 Our Earth in the Universe Life of the stars

  • The universe began approximately 15 billion years ago with an event called the Big Bang which formed a rapidly expanding cloud of mostly hydrogen and helium
  • The hydrogen and helium formed clumps that eventually were drawn together by gravity to form stars.
  • Stars do not last forever—they are created and eventually die. 
  • A smaller star burns longer than a larger star, but only until all of  its hydrogen is converted to helium.  At that point it collapses and then expand again to become a red giant. Its temperature then becomes high enough to burn helium and form carbon and other moderately heavy elements, causing it to collapse again and blow off its outer layer into space, becoming a white dwarf.
  • A large star burns until all of its hydrogen has been converted to carbon and other moderately heavy elements, causing it to expand and become a red supergiant. It then shrinks and becomes much hotter, fusing even the moderately heavy elements until they are converted almost entirely to iron.  At that  point it collapses almost instantaneously so that even heavier elements are formed by fusion, and then explodes violently as a supernova.  All elements heavier than iron were originally formed in such supernovae.

Formation of the Solar System

  • The sun was formed about 5 billion years ago and, since the solar system contains elements heavier than iron, some of the material that came together to form the solar system must have originated in supernovae.
  • As the planets formed, solar wind blew the lighter elements, especially hydrogen and helium, out from the region of the inner planets. As a result the composition of the planets varies with distance from the sun.  The closest planet to the sun, Mercury, is mostly iron. Venus, Earth and Mars have less iron but more moderately heavy elements such as silicon and oxygen. The outer planets, Jupiter, Saturn, Uranus and Neptune, are composed mostly of light elements, primarily in the form of ammonia and methane.

1.4 Formation of the Earth, Moon, and Oceans

  • As the Earth and other planets were first formed, the materials that made up the planets were separated by density layering. The Earth has an iron/nickel core surrounded by a silicon and aluminum rich mantle and then an atmosphere.
  • At first Earth’s atmosphere contained mainly nitrogen, carbon dioxide and other gases but no oxygen. 
  • As Earth cooled water vapor in the atmosphere condensed and fell as rain but quickly evaporated again. This continued for about 25 million years until Earth had cooled sufficiently so that water could accumulate to form the oceans.

Why Oceans on the Earth and Not on Venus or Mars?

  • The Earth has oceans and life, while Mars and Venus do not. This is a result of a delicate balance of factors including the relative sizes of the planets, the relative distances from the sun, their different rates of rotation, and the shape of the planets’ orbits around the sun.
  • Venus is much hotter than the Earth because it has a much higher carbon dioxide concentration in its atmosphere.  Therefore, it has a much stronger greenhouse effect.

Formation of the Moon

  • Early in Earth’s history, about 4.6 billion year ago, a large object collided with the Earth.  The object’s iron and nickel core were incorporated in the Earth but much of the rocky outer mantle of the object was ejected in the collision and became the Moon.

1.5 Oceans and the Origins of Life

  • It is not known how life on Earth first started.  However, it is believed the first organisms may have been chemosynthetic microbes similar to those found at hydrothermal vents and other extreme environments where free oxygen is deficient or unavailable.
  • Life has existed on Earth for about 3.6 billion years, but must have been entirely chemosynthetic until the first photosynthetic organisms developed, perhaps about 3 billion years ago.  Photosynthetic organisms were responsible for altering the chemistry of the atmosphere, which contained little oxygen until about 2 billion years ago.  It took about 1 billion years for the atmosphere to reach its current oxygen concentration.  The oceans and atmosphere have been in a relative steady state since this time, about 1 billion years ago.
  • Invertebrates, the first higher animal life, developed in the oceans about 700 million years ago.  Fishes appeared about 500 million years ago and the first land plants about 70 million years later.  Mammals did not develop until about 220 million years ago and hominids only appeared about 4 million years ago. 

1.6 How to Study Ocean Data Graphs

  • Scientific data is often presented in graphs.  These graphs can be misleading unless you carefully examine the axes.

Contour Plots and Profiles

  • Spatial distributions of variables are often displayed in two dimensional contour plots.
  • The width of spaces between contours in a contour plot provides an indication of the gradient of the plotted parameter.  However, this can be misleading unless you carefully examine the data intervals between the contours.
  • Often, data is contoured and the areas between contours are depicted by colors that represent a range of values.  The convention most often used is that higher values of the contoured parameter are in red, while progressively lower values follow the order of the spectrum of visible light: red, orange, yellow, green, blue, indigo, violet.
  • Vertical distributions are usually represented by profiles which are vertical slices through the Earth or ocean.  Most vertical profiles are vertically exaggerated.

Maps and Charts

  • Locations on Earth’s surface are denoted by an “address” that consists of the coordinates latitude and longitude.
  • Latitude is easily measured, while longitude is expressed in reference to an arbitrary north-south line and can only be measured accurately if an accurate chronometer is available.
  • Distributions of properties on Earth’s surface, which is spherical, are depicted in two dimensions by using a projection.
  • Different projections are used for different reasons, but no projection preserves all four desirable characteristics: relative distances, direction, relative areas, and shapes of Earth’s surface features.

Scientific Notation and Units

  • Scientific notation, in which numbers are expressed as powers of ten, is used to simplify the use of very large or very small numbers which are frequently encountered in Earth sciences.
  • A system of Scientific Units (or SI units) has been developed to standardize the way things are measured.  The system is based on seven basic units.  All other units are derived from these.  Many of the SI units are not yet in universal use but their use is steadily increasing.

 

Critical Concept Reminders:

CC.1 Density and Layering in Fluids

  • The Earth and all other planets are arranged in layers of different materials sorted by their density.

CC.5 Transfer and Storage of Heat by Water

  • The heat properties of water are a critical element in maintaining a climate on Earth that is suitable for life as we know it.

CC.9 The Global Greenhouse Effect

  • Perhaps the greatest environmental challenge faced by humans is the prospect that major climate change may be an inevitable result of our burning of fossil fuels. The burning of fossil fuels releases carbon dioxide and other gases into the atmosphere, where they accumulate and act like the glass of a greenhouse retaining more of the sun’s heat.

CC.10 Modeling

  • Complex environmental systems, including the oceans and atmosphere, can best be studied by using conceptual and mathematical models.

CC.11 Chaos

  • The nonlinear nature of many environmental interactions makes complex environmental systems behave in sometimes unpredictable ways. It also makes it possible for these changes to occur in rapid, unpredictable jumps between one set of conditions and a second, completely different set of conditions.

CC.14 Photosynthesis, Light, and Nutrients

  • Chemosynthesis and photosynthesis are the processes by which simple chemical compounds are made into the organic compounds of living organisms. The oxygen in Earth’s atmosphere is present entirely as a result of photosynthesis.
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