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Earth Science I (INSC 216E) - Introduction |
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Page last updated January 6, 2008
INTRODUCTION
The hydrosphere includes all water on Earth. In one respect, planet Earth is a misnomer in that 71% of the earth is covered by water and only 29% is terra firma. Indeed, the abundance of water on Earth is a unique feature that clearly distinguishes our "Blue Planet" from others in the solar system. Water cannot be found anywhere else in the solar system. It is because the Earth has just the right mass, the right chemical composition, the right atmosphere, and is the right distance from the Sun that permits water to exist mainly as a liquid. However, the range of surface temperatures and pressures of our planet permit water to exist in all three states: solid (ice), liquid (water), and gas (water vapor). Most of the water is contained in the oceans and the high heat capacity of this large volume of water (1.35 million cubic kilometers) is one of the buffers on Earth which alleviates a large temperature range in the change of seasons. Water is the universal solvent and the basis of all life on our Planet.
- Oceans - comprise 71% of surface area of earth
- Open ocean: the major portions away from landmasses, as deep as 11 km in trench areas.
- Coastal ocean: the relatively shallow water next to landmasses on continental shelves. Also includes coastal wetlands.
- Fresh surface water: includes lakes, streams
- Glaciers: includes ice caps currently existing at poles, mountain/valley glaciers elsewhere.
- Ground water: water contained in pore spaces of rocks
The atmosphere is the gasesous envelope that surrounds the Earth and constitutes the transition between its surface and the vacuum of space. The atmosphere consists of a mixture of gases composed primarily of nitrogen, oxygen, carbon dioxide, and water vapor. It extends some 500 km above the surface of the Earth and the lower level (troposphere) constitutes the climate system that maintains the conditions suitable for life on the planet's surface. The next atmospheric level, the stratosphere (12 to 48 km), contains the ozone layer that protects life on the planet by filtering harmful ultraviolet radiation from the Sun. Since the Industrial Revolution, man has been altering the composition of the atmosphere by the burning of fossil fuels. Concern has been growing about rising concentrations of carbon dioxide, methane, nitrous oxide, and chloroflurocarbons in the atmosphere because these "greenhouse" gases trap heat energy emitted from the earth surface and increase global temperatures (global warming). In addition, chloroflurocarbons are effective at depleting the Earth's ozone shield that protects the earth surface from the harmful effects of ultraviolet radiation.
- Troposphere or "weather sphere:" the lowest 10 km of the atmosphere, where we live.
- Stratosphere: a 40-km-thick layer above the troposphere, notable for the ozone layer within it.
- Mesosphere and thermosphere: outer, extremely rarified atmosphere layers that extend upward more than 100 km above the ground surface.
The geosphere is the solid Earth that includes continental and oceanic crust as well as the various layers of the Earth's interior. Ninety-four percent of the earth is composed of the elements oxygen, iron, silica, and magnesium, and the interior of the earth is layered both chemically and mechanically. The geosphere is not static, but its surface (crust) is in a constant state of motion that gives rise to movement of the continents. The unifying theory that explains how continental drift is possible is called plate tectonics, which was developed by geologists in the 1960s.
- Core
- Inner core: solid, probably a dense mixture of iron and nickel
- Outer core: composition evidently similar to inner core, but probably fluid-like, molten or nearly so
- Mantle: solid, rocky, silicate-rich
- Crust: the uppermost few km of the rocky part of the earth.
- Oceanic: relatively thin, dense, uniform thickness and composition. Underlies major ocean basins.
- Continental: variable thickness, less dense than ocean crust so tends to stick up above sea level, and with much higher diversity of rock types. Makes up the large landmasses of the earth.
The biosphere comprises the parts of the above three realms that are inhabited by life: most of the hydrosphere, the lower part of the atmosphere and the upper part of the solid earth. The term "Biosphere" was coined by Russian scientist Vladimir Vernadsky in the 1929. The biosphere is the life zone of the Earth and includes all living organisms, including man, and all organic matter that has not yet decomposed. Life evolved on earth during its early history between 4.5 and 3.8 billion years ago and the biosphere readily distinguishes our planet from all others in the solar system. The chemical reactions of life (e.g., photosynthesis-respiration, carbonate precipitation, etc.) have also imparted a strong signal on the chemical composition of the atmosphere, transforming the atmosphere from reducing conditions to and oxidizing environment with free oxygen. The biosphere is structured into a hierarchy known as the food chain whereby all life is dependent upon the first tier (i.e. mainly the primary producers that are capable of photosynthesis). Energy and mass is transferred from one level of the food chain to the next with an efficiency of about 10%. All organisms are intrinsically linked to their physical environment and the relationship between an organism and its environment is the study of ecology. The biosphere can be divided into distinct ecosystems that represent the interactions between a group of organisms forming a trophic pyramid and the environment or habitat in which they live.
The Anthrosphere - Man and his direct ancestors (hominids) have graced the planet for only about three million years. For almost all of this period the human population totaled less than 5 to 10 million individuals. Homo sapiens have increased their numbers exponentially from 1650 to present rising to the current population of 5.5 billion. If this growth continued unabated, the human population would reach 14 billion in the year 2010, 60 billion in the year 2020, and infinity by the year 2023. Of course, unlimited growth in an environment of finite resources is impossible because growth will eventually deplete the available resources and the population will collapse. Indeed one of the kindest things that the human species could do for planet Earth is to control the rate of growth of the anthrosphere.
EARTH AS A SYSTEM
Different parts of the earth interact by exchanging matter and energy. One example of such interaction is shown by the hydrologic cycle depicting the movements of water among the different spheres of the earth.
- A system is a group of interacting parts within a complex whole. The entire earth could be thought of as a system with many subsystems.
- An interface is a boundary surface across which interactions take place.
- A change in one part of a system tends to produce one or more changes ("responses") elsewhere in the same system, or in interacting systems.
Resources: Every year, each average citizen of a typical developed country consumes many tons of natural resources, such as gold (a few grams), petroleum (a few barrels), rock and other construction materials (a few cubic yards), water (a few thousand gallons) and so on.
- Renewable resources are those that can "grow back" (literally so in some cases, figuratively in others), so that depletion or loss is avoided as long as the rate of consumption stays below the replenishment rate. Most biological or agricultural resources seem to fit in this category.
- Nonrenewable resources are those for which the rate of replenishment (if any) is so slow that the current stock represents all that we have now or ever will have. This group includes most geological resources. Conservation and recycling can extend the length of time that we will be able to make use of such resources.
- Population
- The developed world represents a comparatively small fraction of the total population ofthe earth, but one that consumes several times its proportional "share" of earth resources. Many prognosticators assume that whether by peaceful or violent means, resources will be shared much more equally among countries in the next century or millenium.
- Growth of world population proceeds as an exponential (compound-interest type) of rate. Growth of one to three percent per year is not enough to impress financial investors (unless we are talking about inflation), but such rates are enough to double the world's human population every twenty to forty years. More people translates into more demand for dwindling natural resources, and at the same time it means fewer places where farming or mining can be done.
- Environmental Problems
- Crowding and scarcity of dump-space also result from population growth.
- At the same time that technology helps find new materials to relieve shortages of others that resulted from resource depletion, and per capita waste production rates are increasing, disposal problems become more acute.
THE NATURE OF SCIENTIFIC INQUIRY is based on the presumption that nature operates according to laws that we can identify and understand. The aim of science is to understand nature, basically by identifying natural laws on the basis of what we can observe.
- A hypothesis is a tentative explanation that needs to be tested further or perhaps be modified before it is regarded as valid. A number of rival alternative hypotheses may be formulated to explain the same facts, and one of them eventually accepted.
- A theory is basically a successful hypothesis that appears to be secure from refutation, and commonly offers a basis for advancing to new hypotheses or theories.
- The list of steps making up the scientific method is more of a checklist than a flowchart, recipe or procedure. Many scientific advances have been made by accident or luck, or a chance observation during an investigation of something unrelated to the discovery. One can start with any of the steps in the list and proceed to the others in any order, and some steps may be inappropriate for a particular problem. In other words it doesn't really matter if data are gathered after the hypothesis is formulated. What does matter is that the process remains objective throughout.
THE EARTH SCIENCES include several disciplines that are devoted to the study of the earth, plus aspects of astronomy related to earth studies.
- Geology is the study of basically the solid part of the earth. This includes the study of rocks, minerals, landforms, physical processes on the surface and below, and the natural history of development of the earth.
- Oceanography is the study of the oceans. This rather broad subject area includes disciplines such as marine biology (study of life in the oceans), marine geology (study of geology of the sea floor) and physical oceanography (study of seawater properties, waves, currents, tides).
- Atmospheric Science also includes a number of sub-specialties. Notable among these are meteorology and climatology.
- Astronomy is linked to earth science in that the answers to some questions about the origin and development of the earth may be obtained by studying other planets (planetology). On the other hand answers to some questions about the origin of planets, solar system or bodies beyond may exist here on earth, waiting for us to discover them. At any rate, methods used for study of the earth can be used elsewhere in the universe.
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