Tuesday, June 22, 2010

Problems of Urban growth.

Ranchi the capital city of Jharkhand State in India is expanding both vertical and horizontal resulting in lots of problem.
by
Dr. Nitish Priyadarshi

As more and more people leave villages and farms to live in cities, urban growth results. Urbanization occurs naturally from individual and corporate efforts to reduce time and expense in commuting and transportation while improving opportunities for jobs, education, housing, and transportation. Living in cities permits individuals and families to take advantage of the opportunities of proximity, diversity, and marketplace competition.
People move into cities to seek economic opportunities. In rural areas, often on small family farms, it is difficult to improve one's standard of living beyond basic sustenance. Farm living is dependent on unpredictable environmental conditions, and in times of drought, flood or pestilence, survival becomes extremely problematic.
Cities, in contrast, are known to be places where money, services and wealth are centralized. Cities are where fortunes are made and where social mobility is possible. Businesses, which generate jobs and capital, are usually located in urban areas. Whether the source is trade or tourism, it is also through the cities that foreign money flows into a country. It is easy to see why someone living on a farm might wish to take their chance moving to the city and trying to make enough money to send back home to their struggling family.
There are better basic services as well as other specialist services that aren't found in rural areas. There are more job opportunities and a greater variety of jobs. Health is another major factor. People, especially the elderly are often forced to move to cities where there are doctors and hospitals that can cater for their health needs. Other factors include a greater variety of entertainment (restaurants, movie theaters, theme parks, etc) and a better quality of education, namely universities. Due to their high populations, urban areas can also have much more diverse social communities allowing others to find people like them when they might not be able to in rural areas.

Clearly, urban settlements differ greatly in size, as mentioned by their populations. Is there a Theoretical maximum and an optimum size? Criffith Taylor and others believe that the ultimate size may be fixed by the increasing difficulty of obtaining enough water to supply unduly large numbers concentrated in a small area, while Lewis Mumford and similar authors think that the continued growth of very large cities not only produces more administrative problems than benefits. This also paralyses rather than furthers social relationships and phenomenally raises central land values, so much that land ceases to be adaptable to new needs.

Views on the optimum size of a city have altered with the march of history. Plato believed that most desirable size was 5,000, a figure which would allow everybody to hear the voice of an orator and so participate in active political life and develop varied social relations. Late nineteenth – century garden city enthusiasts in Britain thought that towns of 30,000 to 50,000 would be large enough supply all necessary human needs, whether medical, educational, social, economic or cultural.

Towns could not come into being until the surrounding countryside was capable of providing a food surplus in the past. Due to modern transport and large surpluses in many parts of the world, towns generally have little difficulty in obtaining food, even from far distant lands. Developing countries may lack the capital to give all their town folk an adequate diet, and even in developed countries there are sporadic temporary shortages, owing to failures in economic planning, poor harvests, dock strikes and traffic hold-ups occasioned by excessive rain, snow, floods, droughts etc.

The problem of water supply is more permanent and applies specifically to cities. It is becoming increasingly serious even in advanced countries which certainly have no problem in paying for the water they consume. The root of the problem lies in the fact that 98% of the earth’s surface water is contained in the salt oceans and in ice-caps. The remainder is unevenly distributed and often polluted. Over half is needed for agriculture, about a third for industry, 10 percent for domestic use.

Many cities, especially in developing countries, lack a clean supply of fresh water. In India, e.g., less than a third of the urban population has access to pure water, and the main reason why water borne diseases are rampant. Even when people are provided with purified water for drinking, they usually wash themselves and their clothing in contaminated supplies.

The demands made on water by urban industries, power stations and homes are growing at a more rapid rate than the growth of population. Many wells do not yield enough water, river pollution, like Ganga, Damodar etc. in India, is a continuing evil, and the remaining water resources- mostly in thinly populated highland areas of abundant rain- are far from many consuming centres.

After being separated from Bihar, Jharkhand state of India is now fast growing in terms of business. Ranchi the capital city is expanding both vertical and horizontal resulting in lots of problem like irregular electric supply, water supply, ground water depletion, air pollution, noise pollution, municipal waste disposal, failure of drainage systems, traffic jams etc. Surface waters are being contaminated. Seasonal diseases have also multiplied. More and more people are concentrating in the city flats which has raised the land values many fold. Ranchi earlier known as the summer capital has now become the heat furnace during summer. It is all due to the unplanned expansion of the city.

The urban heat island has become a growing concern and is increasing over the years. The urban heat island is formed when industrial and urban areas are developed and heat becomes more abundant. In rural areas, a large part of the incoming solar energy is used to evaporate water from vegetation and soil. In cities, where less vegetation and exposed soil exists, the majority of the sun’s energy is absorbed by urban structures and asphalt. Hence, during warm daylight hours, less evaporative cooling in cities allows surface temperatures to rise higher than in rural areas. Additional city heat is given off by vehicles and factories, as well as by industrial and domestic heating and cooling units. This effect causes the city to become 2 to 10 degree F (1 to 6 degree C) warmer than surrounding landscapes. Impacts also include reducing soil moisture and intensification of carbon dioxide emissions.
Owing to population growth, poor levels of hygiene, and increasing urban poverty, the urban environment in many developing countries is rapidly deteriorating. Densely packed housing in shanty towns or slums and inadequate drinking-water supplies, garbage collection services, and surface-water drainage systems combine to create favourable habitats for the proliferation of vectors and reservoirs of communicable diseases. As a consequence, vector-borne diseases such as malaria, lymphatic filariasis and dengue are becoming major public health problems associated with rapid urbanization in many tropical countries

Another change that has occurred after the oil crisis of 1973 is the vertical growth of large cities. People who were living in suburbs found it costly to travel to the city. The open spaces within the city got filled up by the construction of high rise buildings. Large bungalows and old residences were demolished and high rise buildings have come up both as commercial complexes and as residential flats. Many rich families are migrating from the suburbs to flats or apartments near the city centre. The vertical expansion of cities poses further problems in water supply, sewage disposal and traffic congestion on the roads. Traffic causes urban noise, air pollution, stress and strain in an individual.

One solution for both lateral expansion and vertical growth of a city is to develop satellite towns at a distance of 40 to 50 km from the city. The satellite town will not be a mere residential town to accommodate commuters. Such a satellite town will be both a place of work and a place of living.

Wednesday, May 26, 2010

What is groundwater dating?

How we calculate age of Groundwater?
by
Dr. Nitish Priyadarshi
photo credit: http://water.usgs.gov/ogw/karst/img/features/arbuckle/vendomeWell.jpg
Groundwater age, based on measurement of the concentrations of chemical and isotopic substances in water, refers to the time elapsed since the introduction of the chemical or isotopic substance into the water, or to be more precise, the time elapsed since the chemical or isotopic substance was recharged and isolated from the modern reservoir. For example, some of the rain that falls on an area percolates (trickles) down through soil and rock until it reaches the water table. Once this water reaches the water table, it moves though the aquifer. The time it takes to travel to a given location, known as the groundwater age, can vary from days to thousands of years.
Although we often refer to dating of groundwater, we are actually dating a chemical substance that is dissolved in the groundwater, not the water itself. Rather than referring to groundwater dating, it would probably be more correct to say we are interpreting temporal aspects of chemical and isotopic substances in groundwater. Isotopes can be separated into environmental isotopes, which are found in the groundwater, and isotopes that are introduced into the ground as a part of a groundwater study.

Environmental isotopes can be either radioactive or stable. They can be used to determine the locations of groundwater recharge areas, circulation patterns in aquifers, sources of dissolved solids in groundwater, and the age of groundwater- the length of time it has been out of contact with the atmosphere.

Various environmental isotopes and tracers are used to determine the age of groundwater. Carbon-14 is used to date groundwater older than 1000 years. Chlorofluorocarbons (Freon) and tritium techniques are used to date groundwater that is less than 50 years old.

Theoretically, ages can be estimated by (1) the travel time of groundwater from the point of recharge to the subsurface point of interest as calculated by Darcy's law combined with an equation of continuity, (2) the decay of radionuclides which have entered the water from contact with the atmosphere, (3) the accumulation of products of radioactive reactions in the subsurface, (4) the degree of disequilibrium between radionuclides and their radioactive daughter products, (5) the time-dependent changes in the molecular structure of compounds dissolved in water, (6) the presence of man-made materials in groundwater, (7) the correlation of paleoclimatic indicators in the water with the known chronology of past climates, and (8) the presence or absence of ions which can be related to past geologic events that have been previously dated. Owing to uncertainties in each of the methods, as many methods as possible should be used in every field situation.

The residence time of water underground has always been a topic of considerable speculation. But with the advent of radioisotopes, determination of the age of groundwater has become possible.

Chlorofluorocarbons-

Hydrologists employ a variety of techniques to measure groundwater age. For relatively young groundwater, chlorofluorocarbons (CFCs) often are used. CFCs are human-made compounds that are stable in the environment. Atmospheric CFC concentrations increased from the time of their development in the 1930s until the 1990s, and hydrologists now know how atmospheric CFC concentrations have changed over time.
CFCs can be used to determine groundwater age because water that is in contact with the atmosphere picks up CFCs from the atmosphere. Thus, CFCs are incorporated in the water before it enters an aquifer. Once water enters an aquifer, it becomes isolated from the atmosphere, and it carries a CFC signature (a distinctive chemical composition) as it travels through the aquifer. This signature reflects the atmospheric concentration when the water was at the surface. By measuring the CFC concentration in groundwater, hydrologists know how long ago the water entered the aquifer.

In the United States and other developed countries, CFCs are being phased out of use because they contribute to atmospheric ozone depletion. As a consequence, atmospheric CFC concentrations have begun to decrease. Atmospheric concentrations of CFCs are not expected to decrease quickly, so CFC dating will continue to work for most young groundwater for many years to come. However, for very young groundwater (groundwater entering aquifers after the late 1990s), CFC dating soon will yield ambiguous results.

Sulfur hexafluoride (SF 6 )-

Hydrologists recently have developed another dating technique that may ultimately replace CFC dating. The new technique uses sulfur hexafluoride (SF 6 ) concentrations in groundwater to determine groundwater age. SF 6 is another stable, human-made compound that has exhibited increasing concentrations in the atmosphere. Unlike CFC concentrations, atmospheric SF 6 concentrations are expected to increase for the foreseeable future. The method, although relatively new, shows promise.

Tritium-

Tritium, 3H, is an unstable isotope of hydrogen with a half life of 12.4 years. It is produced in the upper atmosphere by cosmic radiation; carried to earth by rainfall and hence underground, this natural level of tritium begins to decay as a function of time, such that

A= A0 e-λt

Where A is the observed radioactivity, A0 is the activity at the time the water entered the aquifer, λ is the decay constant, and “t” is the age of the water.

Tritium in the atmosphere is typically in the form of the molecule H3 HO and enters the groundwater as recharging precipitation. Prior to 1953, rainwater had less than 10 tritium units (TU). Starting in 1953, the manufacturing and testing of nuclear weapons have increased the amount of tritium in the atmosphere, with a resulting increasing in tritium in the groundwater. As a result 3H can be used in a qualitative manner to date groundwater in the sense that groundwater with less than 2 to 4 TU is dated prior to 1953 and if the amount is significantly greater than 10 to 20 TU it has been in the contact with the atmosphere since 1953.

Tritium has been used to trace the seepage of contaminated groundwater from low-level nuclear waste disposal areas.

Radiocarbon dating of groundwater (Carbon-14)-

Radiocarbon dating methods can be applied to obtain the age of groundwater. Carbon exists in several naturally occurring isotopes, 12 C, 13 C and 14 C.

Like tritium, carbon 14 is produced in the atmosphere by interaction of cosmic rays with nitrogen, and was introduced in large amounts by nuclear weapons testing. Unlike tritium 14 C has a half life of 5730 years, making it a useful tool for dating water as old as 50,000 years. The 14 C generated in the atmosphere is carried down to the earth’s surface by precipitation, and becomes incorporated into the biomass or transported into water bodies such as lakes, the ocean and groundwater. 14 C undergoes radioactive decay (to 14 N), so that once isolated from the atmosphere, the amount of 14 C decreases with time according to the equation

(14 C)t = (14C)0e –Kt

Where (14 C)t is the amount present at time “t”, (14C)0 is the amount present at t = 0, and K is the decay constant, which is related to the half-life T1/2 by the equation

T1/2 = In2/k
To determine the time since a water was last in contact with atmosphere, it is necessary to know (14 C)0. This is determined by tree rings for the most recent 7000 years; there is no accurate way to determine it prior to 7000 years, so it is generally assumed arbitrarily to have been constant. This gives rise to a time scale in “14 C years”, which may be different from astronomical years.


There are some complications in the behavior of 14 C during recharge, so that the “absolute” age of a groundwater cannot be determined reliably. However, if the 14 C concentration is measured at several points along a flow line within an aquifer, the differences in age between the points and hence the flow velocity can be determined. One complication is that dissolution of carbonate minerals or oxidation of organic matter within an aquifer may add “old” or “dead” (no detectable 14 C) carbon to the water and give an erroneously old age. The contribution of carbon from these sources can sometimes be estimated from 13 C/ 12 C measurements and chemical arguments, so that corrections can be made. Another complication is mixing. A low 14 C concentration may mean that we are looking at relatively “old” water, or it may mean that we are looking at a mixture of relatively “young” water and “dead” water. 14 C measurements can be interpreted as ages only when mixing is insignificant.

Measurements of water samples taken from deep wells in deserts of the United Arab Republic and Saudi Arabia indicate ages of 20,000 to 30,000 years. This period is compatible with the Wisconsin Ice Age, when these desert areas last had high rainfall capable of recharging the underlying major aquifers.

Reference:
Drever, J.I.(1982). The Geochemistry of Natural Waters. Prentice-Hall, Englewood cliffs, NJ.

Thatcher, L. et.al. (1961). Dating desert groundwater. Science 134(3472): 105-106.

Todd, D.K. (1995). Groundwater Hydrology. Wiley, Toronto, pp. 24-25.

Wigley, T.M.L. (1975). Carbon-14 dating of groundwater from closed and open systems. Water Resour. Res. 11: 324-328.

Wigley, T.M.L. (1976). Effect of mineral precipitation on isotopic composition and 14C dating of groundwater. Nature 263: 219-221.
http://www.freedrinkingwater.com/water-education2/6-age-groundwater.htmhttp://www.waterencyclopedia.com/Ge-Hy/Groundwater-Age-of.html

Thursday, May 6, 2010

Distribution of Uranium in world coals.

Jharkhand coal contains trace amount of Uranium in North Karanpura coal field.
by
Dr. Nitish Priyadarshi

Coal is largely composed of organic matter, but it is the inorganic matter in coal—minerals and trace elements— that have been cited as possible causes of health, environmental, and technological problems associated with the use of coal. Some trace elements in coal are naturally radioactive. These radioactive elements include uranium (U), thorium (Th), and their numerous decay products, including radium (Ra) and radon (Rn). Although these elements are less chemically toxic than other coal constituents such as arsenic, selenium, or mercury, questions have been raised concerning possible risk from radiation.


Uranium association with coal has a long history. There is a continuing interest in uranium in coal, because it is a source of radioactivity and because it may be an economic source of uranium. It is just 200 years since the discovery of uranium by M.H. Klaproth. The first detection in coal was by Berthoud (1875) who found up to 2% uranium in coal from near Denver, USA. The samples were collected from a mineralized section of the coal-bed. This mine was soon abandoned.

Subsequent field studies have proven several areas with high uranium coals, especially in the United States, mainly in the Dakotas, Wyoming, Montana, Colorado and New Mexico (Vine,1956). It seems that uranium is carried into the coal swamp in solution as carbonate complexes (Breger, et. al. 1955), which then release uranyl ions to form uranyl-organic complexes. In many coals, especially low-U coals, Uranium is predominantly organically bound.

After World War II, a very intensive uranium search was initiated. The measurement of coal radioactivity were performed in many countries; however only a few are documented. For example, in year 1967 scientists have measured uranium concentration in lignites from Spain (Huesca, Lerida, Ternel, Galicia, Murcia) and reported concentration values 20 to 1200 parts per million (ppm).

Gott (1952) has determined uranium distribution in lignites, shales, and limestones from throughout the US, and a possible mechanism for uranium accumulation in lignites was suggested. Highest uranium concentrations were prevalent in lignites from the Dakotas, Wyoming, and Montana (0.01%), and from high ash Nevada lignite which contained up to 0.05 % uranium. It was postulated that uranium was possibly concentrated in lignite by the action of percolating surface waters after having been leached from volcanic ash.

Uranium bearing coal in the Red Desert area in Wyoming has been studied by Masursky; his findings are documented in several reports. In the first report in year 1952, core and channel samples taken from the Red Desert area in Wyoming were used to investigate the origin of uranium in the coal of the region. Specific uraniferous zones examined included the Sourdough, Monument, Battle, and Luman zones. Areas which were topographically higher and in which coal was overlain by conglomerate showed the highest uranium concentration. Studies of core samples revealed that uranium concentration in the coal beds correlates well with the degree of permeability of adjacent rocks. Where coal beds are overlain or underlain by sandstone, the greatest concentrations of uranium occur at the top and / or bottom of the bed.

J.R. Gill and others in the year 1959 have studied uranium bearing lignite in South Dakota and Montana. They have reported some lignite deposits containing as much as 0.1% uranium.

Coal samples were analyzed for uranium concentration in the coals from the Western United States and approximately 300 coals from the Illinois Basin. In the majority of samples, concentrations of uranium fall in the range from slightly below 1 to 4 parts per million (ppm). Coals with more than 20 ppm uranium are rare in the United States (http://energy.er.usgs.gov/products/databases/ CoalQual/intro.htm).



Results for the uranium in world coals are as follows (Swaine,1990):

Australia- 0.01-4.5 ppm
Brazil- 2.7-19 ppm
Canada- 0.2-7.2 ppm
China- 0.16-21 ppm
Germany West- less than 1 – 13 ppm
India- 1.1-3.6 ppm.
New Zealand- 0.015-0.46 ppm
South Africa- 1.2- 7.3 ppm
Turkey- 1.4-6.4 ppm
UK- 1.1- 3.0 ppm.

Traces of uranium have been also found in the Permian coals of Jharkhand State of India. Areas are KDH, Dakra, Rohini, and Rai Bachra in the North Karanpura coalfield. Channeled samples were analyzed with the help of XRF instrument.

Occurrence of uranium in coals:

Three hypotheses advanced to explain the occurrence of uranium in some coals were described by Denson (1959) as follows.

1. Syngenetic: Uranium was deposited from surface waters by living plants or in dead organic matter in swamps prior to coalification.
2. Diagenetic: Uranium was introduced into the coal during coalification by waters bringing the uranium from areas marginal to the coal deposits or from the consolidating enclosing sediments.
3. Epigenetic: Uranium was introduced in the coal after coalification and after consolidation of the enclosing sediments by groundwater deriving uranium from hydrothermal sources or from unconformably overlying volcanic rocks.
Uranium is associated with clays, zircon and phosphates and may also be organically bound in coal. The accumulation of uranium in coal may vary markedly from place to place, and the occurrence of uranium in each deposit should be interpreted in relation to the geologic history of the region. Field evidence favors the epigenetic hypothesis of the origin of uranium in U.S. western coals. Secondary concentration of uranium in coal may occur when solution of small quantities of uranium by groundwater from overlying volcanic rocks is followed by downward percolation of these waters through previous strata until the uranium is taken up and retained by the highest of the underlying lignite beds. Application of this theory led to the discovery of uranium-bearing coal in Wyoming, Montana, Idaho and New Mexico.
Most thorium in coal is contained in common phosphate minerals such as monazite or apatite. In contrast, uranium is found in both the mineral and organic fractions of coal. Some uranium may be added slowly over geologic time because organic matter can extract dissolved uranium from ground water. In fly ash, the uranium is more concentrated in the finer sized particles. If during coal combustion some uranium is concentrated on ash surfaces as a condensate, then this surface-bound uranium is potentially more susceptible to leaching. However, no obvious evidence of surface enrichment of uranium has been found in the hundreds of fly ash particles examined by USGS researchers.
Most coal also contains potassium-40, lead-210, and radium-226. The total levels are generally about the same as in other rocks of the Earth's crust. Most emerge from a power station in the light flyash, which is fused and chemically stable, or the bottom ash. Some 99% of flyash is typically retained in a modern power station (90% is some older ones), and this is buried in an ash dam.
The amounts of radionuclides involved are noteworthy. In Victoria, 65 million tonnes of brown coal is burned annually for electricity production. This contains about 1.6 ppm uranium and 3.0-3.5 ppm thorium, hence about 100 tonnes of uranium and 200 tonnes of thorium is buried in landfill each year in the Latrobe Valley. Australia exports 235 Mt/yr of coal with 1 to 2 ppm uranium and about 3.5 ppm thorium in it, hence up to 400 tonnes of uranium and about 800 tonnes of thorium could conceivably be added to published export figures (http://www.world-nuclear.org/info/inf30.html).
Other coals are quoted as ranging up to 25 ppm U and 80 ppm Th. In the USA, ash from coal-fired power plants contains on average 1.3 ppm of uranium and 3.2 ppm of thorium, giving rise to 1200 tonnes of uranium and 3000 tonnes of thorium in ash each year (for 955 million tonnes of coal used for power generation). Applying these concentration figures to world coal consumption for power generation (7800 Mt/yr) gives 10,000 tonnes of uranium and 25,000 tonnes of thorium per year(http://www.world-nuclear.org/info/inf30.html).

Reference:
Berthoud, E.L. 1875. on the occurrence of uranium, silver, iron etc., in the Tertiary Formation of Colorado Territory. Proc. Nat. Acad. Sci., Philadelphia, 27, 363-365.
Breger, I.A., Deul, M. and Meyrowitz, R. 1955. Geochemistry and mineralogy of a uraniferous subbituminous coal. Econ. Geol., 50, 610-624.
Bouska, V. 1981. Geochemistry of Coal. Elsevier Scientific Publishing Company, New York.
Denson, N.M., 1959. Uranium in coal in the Western United States, U.S. Geological Survey Bull. 1055.
Gill, J.R. 1959. Reconnaissance for uranium in the Ekalaka Lignite field, Carter County, Montana. US Geological Survey, Bull. 1055.
Gott, G.B. 1952. Uranium in black shales, lignites and limestones in the United States. Selected papers on uranium deposits in the United States. U.S. Geological Survey, Circ.220,Washington. 31-35.
Swaine, D.J. 1990. Trace elements in coal. Butterworths, London.
Valkovic, V. 1983. Trace elements in coal. CRC Press, Inc. Florida.
Vine, J.D. 1956. Uranium-bearing coal in the United States. US Geol. Surv. Prof. Pap., No 300, 405-41.

Saturday, May 1, 2010

Noah's Ark Found in Turkey?

The expedition team is "99.9 percent" sure. Others, well, aren't.
compiled by
Dr. Nitish Priyadarshi
Near the top of Mount Ararat (seen from Armenia in a file photo) in Turkey, explorers claim to have found Noah's ark.
Photograph by Martin Gray, National Geographic
National Geographic News
Published April 28, 2010
A team of evangelical Christian explorers claim they've found the remains of Noah's ark beneath snow and volcanic debris on Turkey's Mount Ararat (map).
But some archaeologists and historians are taking the latest claim that Noah's ark has been found about as seriously as they have past ones—which is to say not very.
Turkish and Chinese explorers from a group called Noah's Ark Ministries International made the latest discovery claim Monday in Hong Kong, where the group is based.
"It's not 100 percent that it is Noah's ark, but we think it is 99.9 percent that this is it," Yeung Wing-cheung, a filmmaker accompanying the explorers, told The Daily Mail.
The team claims to have found in 2007 and 2008 seven large wooden compartments buried at 13,000 feet (4,000 meters) above sea level, near the peak of Mount Ararat. They returned to the site with a film crew in October 2009.
Many Christians believe the mountain in Turkey is the final resting place of Noah's ark, which the Bible says protected Noah, his family, and pairs of every animal species on Earth during a divine deluge that wiped out most of humanity.
"The structure is partitioned into different spaces," said Noah's Ark Ministries International team member Man-fai Yuen in a statement. "We believe that the wooden structure we entered is the same structure recorded in historical accounts. ... "
The team says radiocarbon-dated wood taken from the discovery site—whose location they're keeping secret for now—shows the purported ark is about 4,800 years old, which coincides roughly with the time of Noah's flood implied by the Bible.
On its Web site, Noah's Ark Ministries International says the Turkish government plans to apply to the United Nations to put the Noah's ark discovery site on the UNESCO World Heritage list, a designation given to places of special cultural or physical significance.
Noah's Ark is the vessel which, according to the Book of Genesis, was built by Noah at God's command to save himself, his family, and the world's animals from a worldwide deluge. The Ark features in the traditions of a number of Abrahamic religions, including Judaism, Christianity, Islam, and others.
The Book of Genesis, chapters 6-9, tells how God sends a great flood to destroy the earth because of man's wickedness and because the earth is corrupt. God tells Noah, the righteous man in his generation, to build a large vessel to save his family and a representation of the world's animals. God gives detailed instructions for the Ark and, after its completion, sends the animals to Noah. God then sends the Flood, which rises until all the mountains are covered, and most living things died, except the fish. Then "God remembered Noah," the waters abate, and dry land reappears. Noah, his family, and the animals leave the Ark, and God vowed to never again send a flood to destroy the Earth.

Monday, April 19, 2010

What is Mass Extinction? Are we heading towards other extinction?

Climate change was at the root of some of the major extinction events of the past.
by
Dr. Nitish Priyadarshi

Presently environmentalists are concerned about the imbalance caused by human activity and industrial growth in the ecosystem, as it is slowly inundating the forest cover, thereby reducing considerably the area of natural habitat of animal and plant life. It is also affecting adversely the human community in general as it disturbs the natural cycles of critical materials such as water, oxygen, nitrogen or carbon dioxide. Biocide is occurring at an alarming rate. Experts say that at least half of the world’s current species will be completely gone by the end of the century. Wild plant-life is also disappearing. Most biologists say that we are in the midst of an anthropogenic mass extinction. Numerous scientific studies confirm that this phenomenon is real and happening right now. Should anyone really care? Will it impact individuals on a personal level? Scientists say, “Yes!”
Are we heading towards other extinction as it happened in geological past?

Two main sorts of extinction are recognized – background extinction and mass extinction. The focus here is on mass extinction, observed at intervals throughout Phanerozoic history.

Embedded in the fossil record is a story of adaptation and recovery following catastrophic episodes in which many species become extinct within a geologically short time. Such episodes are called mass extinctions. Most people are aware that the dinosaurs became extinct about 65 million years ago, at the boundary between the Cretaceous (K) and Tertiary (T) periods. But many are not aware that other animal and plant species were also affected. Approximately one-quarter of all known animal families living at the time, including marine and land dwelling species, became extinct at the end of the Cretaceous period. This mass disappearance of species is clearly evident in the fossil record. It is the reason that early paleontologists selected this particular stratigraphic horizon to represent a major boundary in the geological timescale.

The great K-T extinction is not unique, nor was it the most dramatic of such occurrences. There have been at least 5 and possibly as many as 12 mass extinctions during the past 250 million years. The most devastating of these occurred 245 million years ago at the end of the Permian period, when as many as 96 percent of all species died out. Another great extinction occurred at the end of the Triassic period, and several earlier extinctions affected marine organisms.

What causes mass extinctions? Some evidence suggests that the K-T extinction may have been caused by a giant meteorite impact. If an extraterrestrial body such as a meteorite or a comet 10 km in diameter struck the Earth, it could cause massive environmental devastation. The effects could include earthquakes, tsunamis, widespread fires, acid rain, atmospheric particulates that might cause global darkness, and intense climate changes. Evidence for these and related effects has been found in the K-T boundary. Throughout the world the boundary is also marked by a thin layer of clay that is rich in the element iridium (Ir). This is consistent with an influx of extraterrestrial material, because meteorites contain a great deal of iridium compared to the amount contained in terrestrial rocks.

It is possible that a meteorite impact caused the K-T extinction, but the causes of other major extinctions are not as clear. Many scientists feel that some extinctions-particularly the great marine extinctions of the Paleozoic era-were more likely caused by climatic or other environmental changes than by catastrophic events such as meteorite impacts.

The first event recognized by at least some paleontologists as mass extinction actually occurred in Precambrian time. Its exact timing is uncertain, but it happened near the very end of the Proterozoic era. The organisms most notably involved were the soft bodied Ediacarans, although some species of algae seem to disappear at about the same time. If such an event occurred, what was it cause? Sediments from this time period have been examined carefully for excess Ir, which might record an impact, but none has been found. With the available (admittedly scanty) evidence, the best explanation seems to be that the preferred habitat of the Ediacaran animals- shallow water environments-was drastically reduced in amount because of falling sea levels. Analysis of the sediments still preserved from late in Precambrian time suggest that there were repeated cycles of rising and lowering water levels. One of the largest lowerings, also known as regression, during this time appears to coincide with the extinction of the Ediacarans.

Indeed, it is widely believed that sea level change, particularly the lowering of sea level, was a major factor in many of the extinctions in the geologic record. Biological activity is typically high in shallow seas, and times of high sea level provide abundant habitats for marine life, but when the seas withdraw, many of these organisms become extinct. The total range of sea level fluctuations over the past six hundred million years appears to have been very large, at least 200 meters.

The spectacular nature of events at the Cretaceous-Tertiary boundary has tended to obscure the overwhelming importance of the Permian-Triassic extinctions, which saw the end of most of the species then existing in the oceans. The devastation on land was only moderately less extreme. The nature of life on earth was radically changed, and the effects are with us today in the form of all living plants and animals. The cause of this event – or events- are unclear, but it is generally acknowledged that rather severe conditions would have been required to exterminate such a large fraction of life on earth.

The picture that seems to be emerging from Permian-Triassic studies is very different from that of the K-T boundary. The Permian-Triassic record is one of complex extinction patterns in the face of complex and partly interrelated environmental change. No heat, clear-cut culprit has been identified, but much has been learned about the mechanisms of extinction. Nevertheless, the links between cause and effect are still quite tenuous.

The Permian–Triassic (P–Tr) extinction event, informally known as the Great Dying, was an extinction event that occurred 251.4 million years ago, forming the boundary between the Permian and Triassic geologic periods. It was the Earth's most severe extinction event, with up to 96 percent of all marine species and 70 percent of terrestrial vertebrate species becoming extinct; it is the only known mass extinction of insects. Fifty-seven percent of all families and 83% of all genera were killed. Because so much biodiversity was lost, the recovery of life on earth took significantly longer than after other extinction events. This event has been described as the "mother of all mass extinctions". The pattern of extinction is still disputed, as different studies suggest one to three different pulses. There are several proposed mechanisms for the extinctions; the earlier peak was likely due to gradualistic environmental change, while the latter was probably due to a catastrophic event. Possible mechanisms for the latter include large or multiple bolide impact events, increased volcanism, or sudden release of methane hydrates from the sea floor; gradual changes include sea-level change, anoxia, increasing aridity, and a shift in ocean circulation driven by climate change.
Triassic–Jurassic extinction event - 205 Ma at the Triassic-Jurassic transition. About 23% of all families and 48% of all genera (20% of marine families and 55% of marine genera) went extinct. Most non-dinosaurian archosaurs, most therapsids, and most of the large amphibians were eliminated, leaving dinosaurs with little terrestrial competition. Non-dinosaurian archosaurs continued to dominate aquatic environments, while non-archosaurian diapsids continued to dominate marine environments. The Temnospondyl lineage of large amphibians also survived until the Cretaceous in Australia (e.g., Koolasuchus).
At least half of the species now known to have been living on Earth at that time went extinct. This event vacated ecological niches, allowing the dinosaurs to assume the dominant roles in the Jurassic period. This event happened in less than 10,000 years and occurred just before Pangaea started to break apart.
Statistical analysis of marine losses at this time suggests that the decrease in diversity was caused more by a decrease in speciation than by an increase in extinctions.
Several explanations for this event have been suggested, but all have unanswered challenges:
1.
Gradual climate change or sea-level fluctuations during the late Triassic. However, this does not explain the suddenness of the extinctions in the marine realm.
2. Asteroid impact, but no impact crater has been dated to coincide with the Triassic–Jurassic boundary (the impact responsible for the annular Manicouagan Reservoir occurred about 12 million years before the extinction event).
3. Massive volcanic eruptions, specifically the flood basalts of the Central Atlantic Magmatic Province, would release carbon dioxide or sulfur dioxide and aerosols, which would cause either intense global warming (from the former) or cooling (from the latter).


The Late Devonian extinction was one of five major extinction events in the history of the Earth's biota. A major extinction occurred at the boundary that marks the beginning of the last phase of the Devonian period, the Famennian faunal stage, (the Frasnian-Famennian boundary), about 364 million years ago, when nearly all of the fossil agnathan fishes suddenly disappeared.
A second strong pulse closed the Devonian period. Overall, 19% of all families and 50% of all genera went extinct. Although it is clear that there was a massive loss of biodiversity towards the end of the Devonian, the extent of time during which these events took place is uncertain, with estimates ranging from 500,000 to 15 million years, the latter being the full length of the Famennian. Nor is it clear whether it concerned two sharp mass extinctions or a series of smaller extinctions, though the latest research suggests multiple causes and a series of distinct extinction pulses through an interval of some three million years. Some consider the extinction to be as many as seven distinct events, spread over about 25 million years, including particularly notable extinctions at the ends of the Givetian, Frasnian, and Famennian stages.
By the late Devonian, there were plants, insects, and amphibians on land, fish in the seas, and huge reefs built by corals and stromatoporoids. The extinction seems to have only affected marine life. The causes of these extinctions are unclear. The leading theories suggest that changes in sea level and ocean anoxia, possibly triggered by global cooling or oceanic volcanism, were most likely responsible, although the impact of an extraterrestrial body such as a comet has also been considered. Some statistical analysis suggests that the decrease in diversity was caused more by a decrease in speciation than by an increase in extinctions.
The Ordovician–Silurian extinction event or quite commonly the Ordovician extinction, was the third-largest of the five major extinction events in Earth's history in terms of percentage of genera that went extinct and second largest overall in the overall loss of life. Between about 450 Ma to 440 Ma, two bursts of extinction, separated by one million years, appear to have happened . This was the second biggest extinction of marine life, ranking only below the Permian extinction. At the time, all known life was confined to the seas and oceans More than 60 per cent of marine invertebrates died including two-thirds of all brachiopod and bryozoan families. Particularly affected were brachiopods, bivalves, echinoderms, bryozoans, and corals. The immediate cause of extinction appears to have been the continental drift of a significant landmass into the south polar region, causing a global temperature drop, glaciation, and consequent lowering of the sea level, which destroyed species' habitats around the continental shelves. Evidence for this was found through deposits in the Sahara Desert. When Gondwana passed over the south pole in the Ordovician, global climatic cooling occurred to such a degree that there was widespread continental glaciation. This glaciation event also caused a lowering of sea level worldwide as large amounts of water became tied up in ice sheets. A combination of this lowering of sea level, reducing ecospace on continental shelves, in conjunction with the cooling caused by the glaciation itself are likely driving agents for the Ordovician mass extinction. These extinctions are currently being intensively studied; the most commonly accepted theory is that they were triggered by the onset of a long ice age, perhaps the most severe glacial age.
There was other theory too regarding extinction. Scientists from the University of Kansas and NASA have suggested that the initial extinctions could have been caused by a gamma ray burst originating from an hypernova within 6,000 light years of Earth (within a nearby arm of the Milky Way Galaxy). A ten-second burst would have stripped the Earth's atmosphere of half of its ozone almost immediately, causing surface-dwelling organisms, including those responsible for planetary photosynthesis, to be exposed to high levels of ultraviolet radiation. This would have killed many species and caused a drop in temperatures. While plausible, there is no unambiguous evidence that such a nearby gamma ray burst has ever actually occurred.
New Theory On Largest Known Mass Extinction In Earth's History:
The largest mass extinction in the history of the earth could have been triggered off by giant salt lakes, whose emissions of halogenated gases changed the atmospheric composition so dramatically that vegetation was irretrievably damaged. An international team of scientists has reported in the most recent edition of the Proceedings of the Russian Academy of Sciences (Dokladi Earth Sciences). At the Permian/Triassic boundary, 250 million years ago, about 90 percent of the animal and plant species ashore became extinct. Previously it was thought that volcanic eruptions, the impacts of asteroids, or methane hydrate were instigating causes.
The new theory is based on a comparison with today's biochemical and atmospheric chemical processes. According to Dr. Ludwig Weißflog from the Helmholtz-Center for Environmental Research (UFZ) "Our calculations show that airborne pollutants from giant salt lakes like the Zechstein Sea must have had catastrophic effects at that time".

Based on the findings the researchers were able to form their new hypothesis: At the end of the Permian Age the emissions of halogenated gases from the Zechstein Sea and other salt seas were responsible in a complex chain of events for the world's largest mass extinction in the history of the earth, in which about 90 percent of the animal and plant species of that time became extinct.

The Holocene extinction is the widespread, ongoing extinction of species during the present Holocene epoch. The large number of extinctions span numerous families of plants and animals including mammals, birds, amphibians, reptiles and arthropods; a sizeable fraction of these extinctions are occurring in the rainforests. Between 1500 and 2009 CE, 875 extinctions have been documented by the International Union for Conservation of Nature and Natural Resources However, since most extinctions go undocumented, scientists estimate that during the 20th century, between 20,000 and two million species actually became extinct, but the precise total cannot be determined more accurately within the limits of present knowledge. Up to 140,000 species per year (based on Species-area theory) may be the present rate of extinction based upon upper bound estimating.
In broad usage, Holocene extinction includes the notable disappearance of large mammals, known as megafauna, starting 10,000 years ago as humans developed and spread. Such disappearances have normally been considered as either a response to climate change, a result of the proliferation of modern humans, or both.
Over 10,000 scientists in the World Conservation Union have compiled data showing that currently 51 per cent of known reptiles, 52 per cent of known insects, and 73 per cent of known flowering plants are in danger along with many mammals, birds and amphibians. It is likely that some species will become extinct before they are even discovered, before any medicinal use or other important features can be assessed. A new study suggests that global warming could threaten one-fourth of the world's plant and vertebrate animal species with extinction by 2050.

The causes of biocide are a hodge-podge of human environmental “poisons” which often work synergistically, including a vast array of pollutants, pesticides, a thinning ozone layer which increases ultra-violet radiation, human induced climate change, habitat loss from agriculture and urban sprawl, invasions of exotic species introduced by humans, illegal and legal wildlife trade, light pollution, and man-made borders among other many other causes.

There is considerable circumstantial evidence that climate change was at the root of some of the major extinction events of the past. Competition, especially competition for food, is another reason for extinction, although it is unlikely to be a dominant one in mass extinctions. It has been argued that competition was responsible for the minor role played by mammals during the Mesozoic.

The list of possible agents of mass extinction is quite long. It contains mechanisms ranging from the exotic to the ordinary; some examples are explosion of a nearby Supernova, which would have bathed the earth in lethal radiation, the effects of plate tectonics moving continents into and out of favorable climatic belts, and the rise and fall of sea level.

Summary:

Major Extinction Events
1.
488 million years ago : a series of mass extinctions at the Cambrian-Ordovician transition (the Cambrian-Ordovician extinction events) eliminated many brachiopods and conodonts and severely reduced the number of trilobite species.
2. 444 million years ago : at the Ordovician-Silurian transition two Ordovician-Silurian extinction events occurred, and togther these are ranked by many scientists as the second largest of the five major extinctions in Earth's history in terms of percentage of genera that went extinct.
3. 360 million years ago : near the Devonian-Carboniferous transition (the Late Devonian extinction) a prolonged series of extinctions led to the elimination of about 70% of all species. This was not a sudden event the period of decline lasted perhaps as long as 20 million years, and there is evidence for a series of extinction pulses within this period.
4. 251 million years ago : at the Permian-Triassic transition Earth's worst mass extinction (the P/Tr or Permian-Triassic extinction event) killed 53% of marine families, 84% of marine genera, about 96% of all marine species and an estimated 70% of land species (including plants, insects, and vertebrate animals). The "Great Dying" had enormous evolutionary significance: on land it ended the dominance of the mammal-like reptiles and created the opportunity for archosaurs and then dinosaurs to become the dominant land vertebrates; in the seas the percentage of animals that were sessile dropped from 67% to 50%. The whole of the late Permian was a difficult time for at least marine life - even before the "Great Dying", the diagram shows a late-Permian level of extinction large enough to qualify for inclusion in the "Big Five".
5. 200 million years ago : at the Triassic-Jurassic transition (the Triassic-Jurassic extinction event) about 20% of all marine families as well as most non-dinosaurian archosaurs, most therapsids, and the last of the large amphibians were eliminated.
6. 65 million years ago : at the Cretaceous-Paleogene transition (the K/T or Cretaceous-Tertiary extinction event) about 50% of all species became extinct. It has great significance for humans because it ended the reign of the dinosaurs and opened the way for mammals to become the dominant land vertebrates; and in the seas it reduced the percentage of sessile animals again, to about 33%. The K/T extinction was rather uneven some groups of organisms became extinct, some suffered heavy losses and some appear to have got off relatively lightly.
7. Present day : the Holocene extinction event. A 1998 survey by the American Museum of Natural History found that 70% of biologists view the present era as part of a mass extinction event, possibly one of the fastest ever. Some, such as E. O. Wilson of Harvard University, predict that man's destruction of the biosphere could cause the extinction of one-half of all species in the next 100 years. Research and conservation efforts, such as the IUCN's annual "Red List" of threatened species, all point to an ongoing period of enhanced extinction, though some offer much lower rates and hence longer time scales before the onset of catastrophic damage. The extinction of many megafauna near the end of the most recent ice age is also sometimes considered a part of the Holocene extinction event.

Reference:

Bambach, R.K.; Knoll, A.H.; Wang, S.C. (December 2004). "Origination, extinction, and mass depletions of marine diversity". Paleobiology 30 (4): 522–542.

Barry, Patrick L. (January 28, 2002). "The Great Dying". Science@NASA. Science and Technology Directorate, Marshall Space Flight Center, NASA.

Bowring SA, Erwin DH, Jin YG, Martin MW, Davidek K, Wang W (1998). "U/Pb Zircon Geochronology and Tempo of the End-Permian Mass Extinction". Science 280 (1039): 1039–1045.

Cloud, P. 1987. Oasis in space, earth history from beginning. W.W. Norton & Company, New York.

Jin YG, Wang Y, Wang W, Shang QH, Cao CQ, Erwin DH (2000). "Pattern of Marine Mass Extinction Near the Permian–Triassic Boundary in South China". Science 289 (5478): 432–436.

Jr. Dickey, J. S. 1996. On the rocks. John Wiley & Sons, Inc. New York.

Labandeira CC, Sepkoski JJ (1993). "Insect diversity in the fossil record". Science 261 (5119): 310–5.
Macdougall, J.D. 1996. A short history of planet earth, mountains, mammals, fire, and ice. John Wiley & Sons, Inc. New York.

Sole, R. V., and Newman, M., 2002. "Extinctions and Biodiversity in the Fossil Record - Volume Two, The earth system: biological and ecological dimensions of global environment change" pp. 297-391, Encyclopedia of Global Enviromental Change John Wiley & Sons.

Wanjek, Christopher (April 6, 2005). "Explosions in Space May Have Initiated Ancient Extinction on Earth". NASA. http://www.nasa.gov/vision/universe/starsgalaxies/gammaray_extinction.html. Retrieved 2008-04-30.

http://science.nasa.gov/headlines/y2002/28jan_extinction.htm. Retrieved March 26, 2009.
http://en.wikipedia.org/wiki/Extinction_event
http://en.wikipedia.org/wiki/Permian%E2%80%93Triassic_extinction_event
http://en.wikipedia.org/wiki/Late_Devonian_extinction
http://en.wikipedia.org/wiki/Ordovician%E2%80%93Silurian_extinction_event
http://www.sciencedaily.com/releases/2009/03/090330102659.htm
http://news.nationalgeographic.com/news/2006/04/0412_060412_global_warming.html
http://en.wikipedia.org/wiki/Triassic%E2%80%93Jurassic_extinction_event
http://www.dailygalaxy.com/my_weblog/2008/02/the-6th-great-m.html
http://en.wikipedia.org/wiki/Holocene_extinction
http://www.newscientist.com/article/dn4797-earth-faces-sixth-mass-extinction.html
http://life7.beyondgenes.com/