SUMMARY / RELATED TOPICS

Population

In biology a population is all the organisms of the same group or species, which live in a particular geographical area. The area of a sexual population is the area where inter-breeding is possible between any pair within the area, where the probability of interbreeding is greater than the probability of cross-breeding with individuals from other areas. In sociology, population refers to a collection of their entire race. Demography is a social science. Population, in a more simple term, is the number of people in a city or town, country or world. In population genetics a sex population is a set of organisms in which any pair of members can breed together; this means that they can exchange gametes to produce normally-fertile offspring, such a breeding group is known therefore as a Gamo deme. This implies that all members belong to the same species. If the Gamo deme is large, all gene alleles are uniformly distributed by the gametes within it, the Gamo deme is said to be panmictic. Under this state, allele frequencies can be converted to genotype frequencies by expanding an appropriate quadratic equation, as shown by Sir Ronald Fisher in his establishment of quantitative genetics.

This occurs in Nature: localization of gamete exchange – through dispersal limitations, preferential mating, cataclysm, or other cause – may lead to small actual Gamo demes which exchange gametes reasonably uniformly within themselves but are separated from their neighboring Gamo demes. However, there may be low frequencies of exchange with these neighbors; this may be viewed as the breaking up of a large sexual population into smaller overlapping sexual populations. This failure of panmixia leads to two important changes in overall population structure: the component Gamo demos vary in their allele frequencies when compared with each other and with the theoretical panmictic original; the overall rise in homozygosity is quantified by the inbreeding coefficient. Note that all homozygotes are increased in frequency – both the deleterious and the desirable; the mean phenotype of the Gamo demes collection is lower than that of the panmictic original –, known as inbreeding depression. It is most important to note, that some dispersion lines will be superior to the panmictic original, while some will be about the same, some will be inferior.

The probabilities of each can be estimated from those binomial equations. In plant and animal breeding, procedures have been developed which deliberately utilize the effects of dispersion, it can be shown that dispersion-assisted selection leads to the greatest genetic advance, is much more powerful than selection acting without attendant dispersion. This is so for both autogamous Gamo demes. In ecology, the population of some certain species in a certain area can be estimated using the Lincoln Index. According to the United States Census Bureau the world's population was about 7.55 billion in 2019 and that the 7 billion number was surpassed on 12 March 2012. According to a separate estimate by the United Nations, Earth's population exceeded seven billion in October 2011, a milestone that offers unprecedented challenges and opportunities to all of humanity, according to UNFPA. According to papers published by the United States Census Bureau, the world population hit 6.5 billion on 24 February 2006.

The United Nations Population Fund designated 12 October 1999 as the approximate day on which world population reached 6 billion. This was about 12 years after the world population reached 5 billion in 1987, six years after the world population reached 5.5 billion in 1993. The population of countries such as Nigeria is not known to the nearest million, so there is a considerable margin of error in such estimates. Researcher Carl Haub calculated that a total of over 100 billion people have been born in the last 2000 years. Population growth increased as the Industrial Revolution gathered pace from 1700 onwards; the last 50 years have seen a yet more rapid increase in the rate of population growth due to medical advances and substantial increases in agricultural productivity beginning in the 1960s, made by the Green Revolution. In 2017 the United Nations Population Division projected that the world's population will reach about 9.8 billion in 2050 and 11.2 billion in 2100. In the future, the world's population is expected to peak, after which it will decline due to economic reasons, health concerns, land exhaustion and environmental hazards.

According to one report, it is likely that the world's population will stop growing before the end of the 21st century. Further, there is some likelihood that population will decline before 2100. Population has declined in the last decade or two in Eastern Europe, the Baltics and in the Commonwealth of Independent States; the population pattern of less-developed regions of the world in recent years has been marked by increasing birth rates. These followed an earlier sharp reduction in death rates; this transition from high birth and death rates to low birth and death rates is referred to as the demographic transition. Human population control

Absolute dating

Absolute dating is the process of determining an age on a specified chronology in archaeology and geology. Some scientists prefer the terms chronometric or calendar dating, as use of the word "absolute" implies an unwarranted certainty of accuracy. Absolute dating provides a numerical age or range in contrast with relative dating which places events in order without any measure of the age between events. In archaeology, absolute dating is based on the physical and life properties of the materials of artifacts, buildings, or other items that have been modified by humans and by historical associations with materials with known dates. Techniques include tree rings in timbers, radiocarbon dating of wood or bones, trapped-charge dating methods such as thermoluminescence dating of glazed ceramics. Coins found in excavations may have their production date written on them, or there may be written records describing the coin and when it was used, allowing the site to be associated with a particular calendar year.

In historical geology, the primary methods of absolute dating involve using the radioactive decay of elements trapped in rocks or minerals, including isotope systems from young to systems such as uranium–lead dating that allow acquisition of absolute ages for some of the oldest rocks on Earth. Radiometric dating is based on the known and constant rate of decay of radioactive isotopes into their radiogenic daughter isotopes. Particular isotopes are suitable for different applications due to the types of atoms present in the mineral or other material and its approximate age. For example, techniques based on isotopes with half lives in the thousands of years, such as carbon-14, cannot be used to date materials that have ages on the order of billions of years, as the detectable amounts of the radioactive atoms and their decayed daughter isotopes will be too small to measure within the uncertainty of the instruments. One of the most used and well-known absolute dating techniques is carbon-14 dating, used to date organic remains.

This is a radiometric technique. Cosmic radiation entering the earth’s atmosphere produces carbon-14, plants take in carbon-14 as they fix carbon dioxide. Carbon-14 moves up the food chain as predators eat other animals. With death, the uptake of carbon-14 stops, it takes 5,730 years for half the carbon-14 to change to nitrogen. After another 5,730 years only one-quarter of the original carbon-14 will remain. After yet another 5,730 years only one-eighth will be left. By measuring the carbon-14 in organic material, scientists can determine the date of death of the organic matter in an artifact or ecofact; the short half-life of carbon-14, 5,730 years, makes dating reliable only up to about 50,000 years. The technique cannot pinpoint the date of an archeological site better than historic records, but is effective for precise dates when calibrated with other dating techniques such as tree-ring dating. An additional problem with carbon-14 dates from archeological sites is known as the "old wood" problem.

It is possible in dry, desert climates, for organic materials such as from dead trees to remain in their natural state for hundreds of years before people use them as firewood or building materials, after which they become part of the archaeological record. Thus dating that particular tree does not indicate when the fire burned or the structure was built. For this reason, many archaeologists prefer to use samples from short-lived plants for radiocarbon dating; the development of accelerator mass spectrometry dating, which allows a date to be obtained from a small sample, has been useful in this regard. Other radiometric dating techniques are available for earlier periods. One of the most used is potassium–argon dating. Potassium-40 is a radioactive isotope of potassium that decays into argon-40; the half-life of potassium-40 is 1.3 billion years, far longer than that of carbon-14, allowing much older samples to be dated. Potassium is common in rocks and minerals, allowing many samples of geochronological or archeological interest to be dated.

Argon, a noble gas, is not incorporated into such samples except when produced in situ through radioactive decay. The date measured reveals the last time that the object was heated past the closure temperature at which the trapped argon can escape the lattice. K–Ar dating was used to calibrate the geomagnetic polarity time scale. Thermoluminescence testing dates items to the last time they were heated; this technique is based on the principle. This process frees electrons within minerals. Heating an item to 500 degrees Celsius or higher releases the trapped electrons, producing light; this light can be measured to determine the last time. Radiation levels do not remain constant over time. Fluctuating levels can skew results – for example, if an item went through several high radiation eras, thermoluminescence will return an older date for the item. Many factors can spoil the sample before testing as well, exposing the sample to heat or direct light may cause some of the electrons to dissipate, causing the item to date younger.

Because of these and other factors, Thermoluminescence is at the most about 15% accurate. It cannot be used to date a site on its own. However, it can be used to confirm the antiquity of an item. Optically stimulated luminescence dating constrains the time at which sediment was last exposed to light. During sediment transport, exposure to s

Archie W. Dunham

Archie W. Dunham is the former Chairman Emeritus and former Independent Non-executive Chairman of Chesapeake Energy in Oklahoma City, he served as President and Chief Executive Officer of Conoco Inc. from January 1996 to August 2002 as Chairman of ConocoPhillips, following the merger of Conoco Inc. and Phillips Petroleum Company, until his retirement on September 30, 2004. Dunham grew up in Oklahoma. After earning a bachelor's degree in Geological Engineering from the University of Oklahoma in 1960, he was commissioned as a second lieutenant in the United States Marine Corps. Dunham served four years in the Marines returned to the University of Oklahoma to complete an MBA in 1966. Dunham joined Conoco Inc. in 1966 and subsequently held a number of commercial and managerial positions within Conoco and E. I. du Pont de Nemours and Company. Dunham served as senior vice president of polymers and executive vice president of E. I. du Pont de Nemours and Company, Conoco's former parent, from 1995 to October 1998.

Dunham served as executive vice president of exploration production and executive vice president of refining, marketing and transportation for Conoco. He served as chairman, CEO of Conoco Inc. from August 1999 to August 2002 and served as chairman of ConocoPhillips from August 2002, following the merger of Conoco Inc. and Phillips Petroleum Company, until his retirement on September 30, 2004. Dunham was a board director of DuPont, Phelps Dodge, Pride International, Union Pacific and Louisiana-Pacific, he was past Chairman of the United States Energy Association, the National Petroleum Council and the National Association of Manufacturers. Dunham is a member of the board of visitors at the University of Oklahoma, he was a director of the American Petroleum Institute, the U. S.–Russia Business Council and the Greater Houston Partnership. He served on the board of the Memorial Hermann Healthcare System in Houston, the board of visitors of M. D. Anderson Cancer Center, the board of trustees of the Houston Symphony, the George Bush Presidential Library, the Smithsonian Institution.

He served as a trustee of Houston Grand Opera and was a member of The Business Council and The Business Roundtable. He was a former member of the Deutsche Bank advisory board of directors. In 2012, Dunham was appointed Independent Non-executive Chairman of Chesapeake Energy as part of changes to the board of directors following concerns about loans and other corporate governance issues made under the watch of former CEO and chairman Aubrey McClendon; as of 12/21/18, he is the largest non-institutional owner of Chesapeake Energy shares, with a portfolio totaling 9,347,375 shares. On 10/12/15, current Chesapeake former Saks Inc.. Chief Executive Brad Martin was named Non-executive Chairman of its board, succeeding Dunham, who became Chairman Emeritus. Dunham retired from the Chesapeake Energy board on May 17, 2019. Archie and Linda Dunham married in 1960; the couple has three children: Steven and Cary. 1996: Inducted into the University of Oklahoma College of Engineering's Distinguished Graduates Society 1998 Community Partners Houston Father of the Year.

1998: Inducted into Oklahoma Hall of Fame. 1999: Honorary Doctorate in humane letters from the University of Oklahoma. 2000: New York Mercantile Exchange award for CEO of the Year for Global Vision in Energy. 2000: International Achievement Award by B'nai B'rith. 2001: Horatio Alger Association of Distinguished Americans 2001: Ellis Island Medal of Honor. 2004: Greater Houston Partnership International Executive of the Year. 2005: John Rogers Award 2006: Inducted into Offshore Energy Center Hall of Fame. 2011: Houston Baptist University Spirit of Excellence Award