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An alternative to ocean fishing is aquaculture , a method in which fish and shellfish are deliberately raised for food. There are two types of aquaculture: fish farming and fish ranching. With fish farming , the fish or shellfish (e.g. carp, catfish, oysters) are raised in closed ponds or tanks with a controlled environment. When they reach maturity they are harvested. Fish ranching is used with species such as salmon that live one part of their lives in freshwater and the other part in salt water ( anadromous species ). Salmon are raised in captivity for a few years and then released. They are harvested when they return to spawn. Some of the disadvantages of aquaculture include the need for supplying large amounts of food and water, and disposal of the large amounts of waste that are produced.

Algae into oil, bones into stones

Scientists and textbooks tend to separate biological and geological entities and processes, but the complex cycling of matter on Earth actually blurs those categories. Indeed, some of our most important energy and mineral resources have biological origins. As a consequence, the location and size of these resources depends upon the distribution and productivity of ancient habitats.

Petroleum

Petroleum is a generic term for oil and natural gas, and their products. Petroleum doesn’t look organic, but it is derived from the remains of countless marine organisms. It begins with blooms of microscopic algae and other plankton in oceans and large lakes. These organisms sink when they die, and if the seafloor or lakebed they land on has low oxygen and high sedimentation, they can be buried in mud before they decompose. At depth and over time, heat and pressure begin to convert the organic molecules into hydrocarbons. The hydrocarbons begin to liquefy into oil at 50-60° C, and vaporize into methane at 100° C. If the temperature exceeds 200° C, they break down and disappear.

Where petroleum is abundant, it can be pumped from below ground and refined into fuels such as gasoline, propane, jet fuel, and heating oil, and into tar and asphalt. Petroleum is also a component of plastics, dyes, synthetic fibers, fertilizers, compact discs, cosmetics, and explosives.

Petroleum is extremely useful, but it is unevenly distributed around the world, and reserves are being depleted rapidly. Petroleum formation is a complex process that requires just the right biological conditions to produce sufficient plankton, and just the right geologic conditions to preserve and cook the organic matter. The entire sequence takes a million years or more. Because many countries, like the United States, have very limited deposits, and because all petroleum reserves are being drained rapidly, conservation and alternatives are gaining importance. For instance, worn highway asphalt is now being reprocessed and replaced rather than discarded. Plastic recycling is becoming more widespread. Wind, solar, nuclear, geothermal, and hydroelectric power is increasing.

Limestone

Limestone is a type of rock made of calcium carbonate. Although few things seem less life-like than rocks, most limestone is actually biogenic, formed from the shells and skeletons and excretions of marine invertebrates. In the shallows around tropical islands and continents, warm clear water, strong sunlight, and abundant nutrients allow mollusks, crustaceans, and plankton to flourish. When these creatures die or molt, their hard parts fall to the sea floor. As the remains pile up, the weight of the overlying debris compacts the deepest layers. Cements precipitate out of groundwater, fusing the individual fragments into solid rock. Some limestone goes no further, so that the component shells remain distinct and clearly visible. In other limestone, subject to more intense heat and pressure, the organic material is recrystallized into a featureless mass.

Limestone is widely used in industrial processes. Crushed limestone is a component of cement, paper, plastic, and paint, and is used to adjust the pH of soil and water. Whole limestone that retains visible shell material is used for decorative stonework. Common blackboard chalk is a limestone made from microscopic skeletons.

Limestone is extremely abundant, making up about 10-15% of all sedimentary rocks on Earth, so that even though it is heavily used, its reserve are not being significantly depleted.

Questions & Answers

identify and quantify five social costs and social benefits of building a school
Mokgobo Reply
identify and quantity five social costs and social benefits of building a hospital
Mokgobo
short run vs long run
Jean
is it true that the opportunity cost of unemployed labour is zero?
Wisdom Reply
no
Oigebe
give two forms of collusion
nondumiso Reply
1.Explicit Collusion: Also termed overt collusion, this occurs when two or more firms in the same industry formally agree to control the market .
Gafar
2.Implicit Collusion: Also termed tacit collusion, this occurs when two or more firms in the same industry informally agree to control the market, often through nothing more than interdependent actions. A prime example of implicit collusion is price leadership .
Gafar
explicit collusion: this occurs when two or more firms in the same industry legally agree to control the market
Panashe
implicit collusion this occurs when two or more firms in the same industry illegally agree to control the market
Panashe
what is responsible for investigating cases of collusion
nondumiso
reasons why a country maybe involved in international trade
Nde Reply
state five similarities and differences between money market and capital market
Victoria Reply
Give a Zimbabwean example of firms operating in an oligopoly market and illustrate using diagrams how a manager in such a market maximize profit
Pam Reply
what is an industry
EWAH Reply
An industry is the production of goods and related services within an economy
Prabhu
an industry is place where goods and services are produced for human consumption....
Usman
scarcity is the major course of economics problems. discuss
Abdulhameed Reply
please say about that it is interesting for us
Abayneh
what is economics
Michael Reply
economics is a social sciences that deals with the production distribution and consumption of goods and services produced.its study of behaviour between economic agents
rkesh
what is the formula for elasticity of demand
Ridwan
change in demand/change in variable variable may be price, income,
rkesh
seasonal unemployment
Enoch Reply
example agriculture
lungku
want and scarcity
Prince
why the average of revenue AR fun
Abba
What is monopoli
Gadrey Reply
What is monopoly
Gadrey
monopoly
Hanan
monipoly ..where one firm controls all the market
RAM
what is demand
Jafar Reply
demand is what one willing and enable to purchase at a given price over period of a time.
Micheal
what is marginal revenue
just
distinguish between commercialization and industrialization
Alhassan Reply
why division of labour increase economy level of production
Henry Reply
what is opportunity coast
Henry Reply
a benefit profit or value of something that must be given up to acquire achieve something else
ammara
thx
Henry
in a comparison of the stages of meiosis to the stage of mitosis, which stages are unique to meiosis and which stages have the same event in botg meiosis and mitosis
Leah Reply
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Source:  OpenStax, Ap environmental science. OpenStax CNX. Sep 25, 2009 Download for free at http://cnx.org/content/col10548/1.2
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