Dating фа

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This website was inspired by an episode of Fat Friends, the TV series. It was the one where Jamie meets up with a lady, after seeing her advert on an online singles dating website. Needless to say things got very hot!

It's free to search members photo's and profiles. Find friendship, romance, marriage or just some excitement. It's free, simple, confidential and quick to place your own personals advert.

Fat Friends Dating. It's free! Fat Friends - Fat Dating to Meet Fat Singles and BBW BHM FA FFA. Search members photo's, profiles and personals adverts. Great for fat people who are single and who want to meet fat friends and find relationships.

Find friendship, romance, love, marriage or just some excitement. Great for fat women, fat girls and fat men. Are you chubby, big, weight, fat, large, bbw, fatter, large's, fattest, fat's, bbw's, well-made, heavy, large, obese, oversize, paunchy, plump, portly, solid, stout, thickset or just a lttle bit tubby? Fat Friends Dating. It's free to search members photo's and profiles. It's free to place your own personals advert.

Are you looking for friendship, romance, love, marriage or just some excitement. Great for fat women, fat girls and fat men. Great for fat people who are single and who want to meet fat friends and find relationships. Are you chubby, big, well-made, heavy, large, obese, oversize, paunchy, plump, portly, solid, stout, thickset or tubby?

Dating for mжnd og kvinder over 40 еr

Opret en datingprofil

Din datingprofil skal vжre жrlig og du skal tжnke godt over, hvad du egentlig шnsker af din kommende partner, ligesom det er vigtigt at du tжnker over hvad du kan give en kжreste. Du skal vжre modig og ikke lade dig begrжnse af hvad andre tжnker. Det er meget vigtigt at du er dig selv - dit kommende forhold skulle jo gerne vare ved.

Nеr du opretter dig skal du vжlge et brugernavn, og her er det vigtigt at du finder noget sжrligt, og meget gerne noget, som du har et forhold til. ”Storbycowboy” siger noget mere (og andet) end ”Sшd fyr”, ligesom ”Kunstnerpigen” siger mere end ”Sшd tшs”.

Nеr du laver din beskrivelse, skal du undgе klichйer som ”jeg elsker naturen”. Beskriv i stedet, hvad du elsker ved naturen, og gшr dig umage for at lave en profil, som fortжller hvem du er, og hvad du kan tilbyde. Tжnk pе, at din drшmmemand eller drшmmekvinde skal blive interesseret i at lжre dig bedre at kende. Det mеl opnеr du bedst ved at lave en profil, som beskriver dine interesser, dit livssyn og dine vжrdier. Forelskelsen kan i det smе opstе allerede ved lжsningen af profilen, og mеlet med din profil er jo at komme pе date.

Et billede siger mere end 1000 ord, og dit profilbillede er meget vigtigt! Fе en god ven eller veninde til at tage et rigtig godt billede af dig, i de omgivelser du gerne vil forbindes med.

» Er du klar til at oprette en profil. Sе klik her!

Dating

En ting er at skrive og chatte pе nettet, en anden er at mшdes i virkeligheden. Nеr I mшdes, sе vжr dig selv, og lad vжre med at skrue forventningerne op. Det er sjжldent at mшde sin kommende livsledsager ved fшrste mшde, men han eller hun skal nok dukke op! Det er en god idй at mшdes pе neutral grund, f. eks. et sted hvor man kan gе en tur og snakke i fred og ro. Det er vigtigt at I kan koncentrere jer om hinanden, ogsе selv om det mеske ikke lige er det helt store.

Lad fordommene blive hjemme. Hvis han eller hun fortжller med begejstring om en fodboldkamp, sе lжg mжrke til begejstringen, selvom du egentlig havde foretrukket at snakke om opera. Det er helt klart vigtigt, at I har nogle fжlles interesser og vжrdier, men det er ogsе vigtigt at I begge er klar til at give hindanden plads og acceptere hinandens forskelligheder.

Nеr man er over 40 еr gammel kan mеlet med dating i DK vжre at finde en kжreste for resten af livet, og et godt parforhold er givende pе sе mange omrеder at det er vжrd at kжmpe for. Lad vжre med at give op, blot fordi du efter nogle dates endnu ikke har mшdt nogen du blev forelsket i: Han eller hun findes derude, og du skal nok finde den rigtige!

Netdating tager tid, man skriver og chatter, og sе afhжnger det hele alligevel af det fшrste mшde. Et godt alternativ kan vжre at deltage i singlefester eller singlerejser, hvor du fra dag 1 mшder andre som ogsе savner en kжreste, og deltager med samme mеl som dig: At finde den eneste ene. Det er derfor, vi ogsе har en afdeling pе siden med de bedste single arrangementer for folk over 40.

» Hvis du vil ind og kigge, sе klik her for at oprette profil. Det er gratis.

40plus – dating og venskaber for voksne

Nеr du opretter en profil pе www.40plus. dk opnеr du en lang rжkke fordele i kunsten at finde kжrligheden. Du kan oprette dig gratis, og med over 50.000 aktive profiler skulle det vжre mжrkeligt, om ikke du ogsе kan finde din kжreste her.

40plus blev grundlagt i 2006 med шnsket om at hjжlpe med at skabe fжllesskaber, bеde i kжrligheden, men ogsе blandt folk over fyrre med samme hobby eller interesse. Det mе her i 2014 siges at vжre en sucess: Vi fеr hver dag tilbagemeldinger fra glade 40plus'ere, der har fundet kжrlighed og nye venskaber her pе 40plus.

40plus er i dag Danmarks stшrste mшdested for folk over 40 еr - det er derfor vi med stolthed har valgt mottoet:

40plus - hvor voksne mшdes!

Dating

Dating is a ritualized courting process that developed in the twentieth century as a means for adolescents to engage in approved heterosexual activities. It emerged first in the United States in response to significant social and gender changes in schooling and work, family life, and recreational activities. During the twentieth century, dating spread to other Westernized societies, although it has become increasingly attenuated in the context of the revolution in premarital sexual behavior after the 1960s.

In the early modern world most courtship was supervised by family or other adult community institutions. Formally arranged marriage was never the dominant practice among most Americans, as it was among the European aristocracy and upper middle class, but informal arrangements existed which directed young people's desires toward suitable partners who remained within racial, class, and other boundaries. Most young people did not have either the time or the privacy to engage widely in experimental activities, and the importance of chastity for women among respectable people meant that girls and young women did not venture very far on their own without adult chaperones. These informal controls were able to adapt initially to the emergence in the nineteenth century of the ideal of romantic LOVE and to companionship as a replacement for patriarchy in marital values. More challenging were the dramatic dislocations that accompanied the urban and industrial transformations of the second half of the nineteenth century.

Among the wealthy elite, well-orchestrated rituals surrounding elaborate debutante balls and coming-out ceremonies largely assured that family choices would continue to define the horizons of adolescents and young adults as they moved toward a season of courtship. Thus eighteen - and nineteen-year-old girls were introduced to the proper society from among whom they could choose and be chosen. But among others, especially the large and growing middle class and the respectable working class, the fact that young men and women spent more time away from the watchful guidance of parents became a source of considerable cultural concern and anxiety in the late nineteenth and early twentieth century, a concern most effectively articulated by social reformer J ANE A DDAMS in The Spirit of Youth in the City Streets. Especially problematic was the new freedom of young women. Both boys and girls were now more often found mixing promiscuously in unsupervised work and play environments as adolescent girls went out to work in factories, shops, and offices. These young people often spent their money and free time in unsupervised commercial recreations such as MOVIES . dance halls, and amusement parks. Both male and female adolescents were also staying in school longer as new school attendance laws began to include more older children. The schools, pressed to engage their charges, provided more opportunities for socializing as they searched for ways to keep older and recalcitrant student populations at school. As schools became the arenas for extracurricular clubs, SPORTS . PROMS . and other events, they also became the site for spontaneous heterosexual socializing. Young people developed dating in these new work and educational contexts as a means to order mate selection and to contain the erotic possibilities that the new freedom from adult supervision made possible.

The apparent freedom of dating and its association with out-of-home and paired activities made the new practice seem risqué and daring in the early twentieth century. By the 1920s, however, it had become generally regarded as a legitimate means of interaction between young men and women during later adolescence and young adulthood. Some immigrant and religious groups still resisted and were appalled by the freedom that dating permitted between strangers, but most native white young people understood that while dating was not supervised by adults it nevertheless had clearly established boundaries enforced by peers that regulated respectability, eligibility, and the routines of sexual access. Moreover, the young not only defined what was attractive, permissible, and popular, but continued to maintain clear class, racial, and ethnic boundaries.

The vast extension of schooling between the world wars to the majority of adolescents (including immigrants) in public HIGH SCHOOLS . and to a substantial minority in colleges and universities, made these new peer definitions possible. The long hours at school and the shift of authority from home and work to youth-based institutions, along with the coeducational nature of the great majority of these institutions, made peer standards in dating dominant. At schools, a complex social system that included extracurricular activities, sports competitions, fraternities and sororities, literary activities, beauty contests, and other means to define identity and popularity regulated dating behavior. But the system was not closed since the young drew on nonschool institutions for inspiration in setting new nonfamily-based fads and fashions. These relied on both the heterogeneity of populations at school and the enormous expansion of popular culture, especially via movies, popular music, and sports, that provided sources and models for approved behavior, appearance, style, language, dress, and beliefs around which standards of popularity and datability revolved. In expanding the vocabulary of acceptable and proper behavior, popular culture idols helped the young redefine eligibility and expand the limits on sexual propriety in their dating behavior toward more liberated forms.

Starting in the 1920s, a date usually involved one or two couples going out together to a movie, a dance, a soda shop, or a roadside restaurant. In places outside of large cities, this increasingly relied on access to an automobile and became dependent on the outlay of significant amounts of cash to ensure that the treat for the afternoon or evening was acceptable to the dating partner. Commercial considerations were thus embedded into the very structure of the dating relationship, which required that the male treat the female to a good time. Women too were required to expend money on their appearance, wearing fashionable clothes and stylish hairdos, and relying on beauty treatments and up-to-date cosmetics. These consumer-based standards became crucial to the evaluations that each side made of the prospective date and the subsequent decisions about whether dating would continue. They were the basis for at least initial conclusions before other, more subtle, considerations could intervene.

In the 1920s and 1930s, exclusivity was not considered either essential to dating or its only necessary result. Instead, a dating-and-rating syndrome sometimes overwhelmed the long-term courtship objectives of dating, as young men and women of the middle class engaged in a whirl of heterosexual social activities which defined their status in a complex hierarchy of popularity and desirability. Class differences also surfaced, particularly in high school, with working-class youth more likely to see dating as part of marriage-partner selection, while middle-class youth engaged in dating more in terms of entertainment. At the same time, both dating which led to exclusive attachments and dating which was part of a busy social life included a variety of erotic practices that became a standard part of the expected sexual initiation of twentieth-century youth before the premarital sexual revolution of the late 1960s and 1970s.

Some historians have argued that in return for the expenses incurred by the male dating partner some sexual compensation was expected from the female. Whether the exchange was quite so direct and calculated or evolved from a set of expanded possibilities for intimacy and graduated expectations, dating certainly resulted in mutual sexual experimentation. In most cases, these activities fell short of intercourse, involving instead an elaborate pattern of sexual play that included hand-holding, kissing, petting, and fondling. It was well understood that within this evolving pattern women would define the limits of acceptable behavior, while men would try to push those boundaries as far as possible. Most studies of the 1920s and 1930s show that among those whose dating had become exclusive, especially those who were engaged to marry, intercourse would become an occasional or regular part of the dating relationship for about half of these couples. This was usually rationalized as a legitimate expression of the commitment to a long-lasting loving relationship oriented to marriage.

These newly established dating rituals were disrupted by America's entry into World War II, when dating was largely suspended for older couples in the context of a national emergency which emptied schools, colleges, factories, and offices of eligible young men. The war also encouraged more rapid sexual involvement and a rush to marriage. In a related way, war often led to short-term casual sex that some young women saw as their contribution to the war effort, but that seemed to liberate others from the artificial standards that had previously been in place. Among these were thousands of VICTORY GIRLS . urban camp followers who catered to men on short-term leave, and whom the army targeted as potential carriers of VENEREAL DISEASE .

Adolescents, though not so clearly affected by the war, were not entirely shielded from its effects, especially since older adolescents might be inducted as the war accelerated draft call-ups. More significantly, the war changed the pattern of delayed marriage that had become common for all classes and groups during the Depression of the 1930s and the postponement of first conception that had a longer twentieth-century history. After the war, the trend toward early marriage continued and in the 1950s a dramatic baby boom altered American family life in significant ways. While peacetime conditions allowed a return to earlier dating behavior, that behavior had now become more than in the past a matter of adult concern and intervention. It was also shorter since women now married younger than at any time in American history and began to contemplate the road to marriage throughout adolescence. Dating as a route to marriage became both more serious and more hurried. Younger adolescents and even preteens began to appropriate some of their older brothers' and sisters' behaviors, while serious relations became more common earlier in the dating process. Pinning (wearing the fraternity or club pin of a boyfriend), wearing a love anklet, and going steady became regular rituals of 1950s and 1960s dating behavior.

At the same time, adults became more clearly involved in these behaviors. The most obvious form this took was in the elaboration of advice in newspapers, TEEN MAGAZINES . and manuals for adolescents. Adult family and relationship experts, who drew on the increasing American infatuation with the science of psychology as a guide to daily life, intervened in this as in many other arenas of child rearing and self-development. But popular culture too began to reflect new concerns about dating, and a whole genre of movies, including films such as the teen classics Where the Boys Are, and Splendor in the Grass, were based on the erotic charge that resulted from breaking dating taboos.

This whole structure was fundamentally weakened in the late 1960s and 1970s when the rapid legitimization of premarital sexuality removed some of the need for dating etiquette, at least among young adults. For adolescents, too, the more open sexuality that developed during this period made dating rules far less stringent and enforceable. While dating certainly continued and continues to define many heterosexual relationships, the rules became much more flexible (and included the possibility of same-sex dating). The effective use of BIRTH CONTROL and the availability of abortion, even for adolescents, after the 1970s meant that rules which had been in place for most of the century and whose objective was always to maintain social standing during a life-cycle phase marked by sexual desire, were hardly as necessary any-more.

While dating has by no means disappeared even in the twenty-first century as adolescents and young adults seek to define just what is permissible and what is not in their mating behavior as they move toward adult life, it now coexists with a range of other activities. Some of these are less dependent on isolated pairing and include group activities associated with alcohol, DRUGS . and music. Matchmaking and dating services–many newly dependent on computers and the Internet–have also become much more common and acceptable. Dating has in the meantime shifted to older people, many of whom seek companionship and remarriage after divorce. Dating has become less obviously part of adolescence as age of marriage has once again shifted upward and taboos against premarital sexuality have become less harsh and judgmental.

BIBLIOGRAPHY

Addams, Jane. 1972 [1909]. The Spirit of Youth in the City Streets. Urbana: University of Illinois Press.

Bailey, Beth L. 1988. From Front Porch to Back Seat: Courtship ind Twentieth-Century America. Baltimore, MD: Johns Hopkins University Press.

Bailey, Beth L. 1999. Sex in the Heartland. Cambridge, MA: Harvard University Press.

Fass, Paula S. 1977. The Damned and the Beautiful: American Youth in the 1920s. New York: Oxford University Press.

Glenn, Susan A. 1990. Daughters of the Shtetl: Life and Labor in the Immigrant Generation. Ithaca, NY: Cornell University Press.

Hine, Thomas. 1999. The Rise and Fall of the American Teenager: A New History of the American Adolescent Experience. New York: Bard.

Modell, John. 1989. Into One's Own: From Youth to Adulthood in the United States, 1920–1975. Berkeley and Los Angeles: University of California Press.

Peiss, Kathy. 1987. Cheap Amusements: Working Women and Leisure in Turn of the Century New York. Philadelphia: Temple University Press.

Rothman, Ellen K. 1984. Hands and Hearts: A History of Courtship in America. New York: Basic Books.

Tentler, Leslie Woodcock. 1979. Wage-Earning Women: Industrial Work and Family Life in the United States, 1900–1930. New York: Oxford University Press.

Circular Reasoning or Reliable Tools?

Overview

Introduction

his document discusses the way radiometric dating and stratigraphic principles are used to establish the conventional geological time scale. It is not about the theory behind radiometric dating methods, it is about their application . and it therefore assumes the reader has some familiarity with the technique already (refer to "Other Sources" for more information). As an example of how they are used, radiometric dates from geologically simple, fossiliferous Cretaceous rocks in western North America are compared to the geological time scale. To get to that point, there is also a historical discussion and description of non-radiometric dating methods.

The example used here contrasts sharply with the way conventional scientific dating methods are characterized by some critics (for example, refer to discussion in "Common Creationist Criticisms of Mainstream Dating Methods " in the Age of the Earth FAQ and Isochron Dating FAQ ). A common form of criticism is to cite geologically complicated situations where the application of radiometric dating is very challenging. These are often characterised as the norm, rather than the exception. I thought it would be useful to present an example where the geology is simple, and unsurprisingly, the method does work well, to show the quality of data that would have to be invalidated before a major revision of the geologic time scale could be accepted by conventional scientists. Geochronologists do not claim that radiometric dating is foolproof (no scientific method is), but it does work reliably for most samples. It is these highly consistent and reliable samples, rather than the tricky ones, that have to be falsified for "young Earth" theories to have any scientific plausibility, not to mention the need to falsify huge amounts of evidence from other techniques.

This document is partly based on a prior posting composed in reply to Ted Holden. My thanks to both him and other critics for motivating me.

Background

Stratigraphic Principles and Relative Time

Much of the Earth's geology consists of successional layers of different rock types, piled one on top of another. The most common rocks observed in this form are sedimentary rocks (derived from what were formerly sediments), and extrusive igneous rocks (e. g. lavas, volcanic ash, and other formerly molten rocks extruded onto the Earth's surface). The layers of rock are known as "strata", and the study of their succession is known as "stratigraphy". Fundamental to stratigraphy are a set of simple principles, based on elementary geometry, empirical observation of the way these rocks are deposited today, and gravity. Most of these principles were formally proposed by Nicolaus Steno (Niels Steensen, Danish), in 1669, although some have an even older heritage that extends as far back as the authors of the Bible. A few principles were recognized and specified later. An early summary of them is found in Charles Lyell's Principles of Geology. published in 1830-32, and does not differ greatly from a modern formulation:

The principle of superposition - in a vertical sequence of sedimentary or volcanic rocks, a higher rock unit is younger than a lower one. "Down" is older, "up" is younger.

The principle of original horizontality - rock layers were originally deposited close to horizontal.

The principle of original lateral extension - A rock unit continues laterally unless there is a structure or change to prevent its extension.

The principle of cross-cutting relationships - a structure that cuts another is younger than the structure that is cut.

The principle of inclusion - a structure that is included in another is older than the including structure.

The principle of "uniformitarianism" - processes operating in the past were constrained by the same "laws of physics" as operate today.

Note that these are principles . In no way are they meant to imply there are no exceptions. For example, the principle of superposition is based, fundamentally, on gravity. In order for a layer of material to be deposited, something has to be beneath it to support it. It can't float in mid-air, particularly if the material involved is sand, mud, or molten rock. The principle of superposition therefore has a clear implication for the relative age of a vertical succession of strata. There are situations where it potentially fails -- for example, in cave deposits. In this situation, the cave contents are younger than both the bedrock below the cave and the suspended roof above. However, note that because of the "principle of cross-cutting relationships". careful examination of the contact between the cave infill and the surrounding rock will reveal the true relative age relationships, as will the "principle of inclusion" if fragments of the surrounding rock are found within the infill. Cave deposits also often have distinctive structures of their own (e. g. spelothems like stalactites and stalagmites), so it is not likely that someone could mistake them for a successional sequence of rock units.

These geological principles are not assumptions either. Each of them is a testable hypothesis about the relationships between rock units and their characteristics. They are applied by geologists in the same sense that a "null hypothesis" is in statistics -- not necessarily correct, just testable. In the last 200 or more years of their application, they are often valid, but geologists do not assume they are. They are the "initial working hypotheses" to be tested further by data.

Using these principles, it is possible to construct an interpretation of the sequence of events for any geological situation, even on other planets (e. g. a crater impact can cut into an older, pre-existing surface, or craters may overlap, revealing their relative ages). The simplest situation for a geologist is a "layer cake" succession of sedimentary or extrusive igneous rock units arranged in nearly horizontal layers. In such a situation, the "principle of superposition" is easily applied, and the strata towards the bottom are older, those towards the top are younger.

Figure 1. Sedimentary beds in outcrop, a graphical plot of a stratigraphic section, and a "way up" indicator example: wave ripples.

This orientation is not an assumption, because in virtually all situations, it is also possible to determine the original "way up" in the stratigraphic succession from "way up indicators". For example, wave ripples have their pointed crests on the "up" side, and more rounded troughs on the "down" side. Many other indicators are commonly present, including ones that can even tell you the angle of the depositional surface at the time ("geopetal structures"), "assuming" that gravity was "down" at the time, which isn't much of an assumption :-).

In more complicated situations, like in a mountain belt, there are often faults, folds, and other structural complications that have deformed and "chopped up" the original stratigraphy. Despite this, the "principle of cross cutting relationships" can be used to determine the sequence of deposition, folds, and faults based on their intersections -- if folds and faults deform or cut across the sedimentary layers and surfaces, then they obviously came after deposition of the sediments. You can't deform a structure (e. g. bedding) that is not there yet! Even in complex situations of multiple deposition, deformation, erosion, deposition, and repeated events, it is possible to reconstruct the sequence of events. Even if the folding is so intense that some of the strata is now upside down, this fact can be recognized with "way up" indicators.

No matter what the geologic situation, these basic principles reliably yield a reconstructed history of the sequence of events, both depositional, erosional, deformational, and others, for the geology of a region. This reconstruction is tested and refined as new field information is collected, and can be (and often is) done completely independently of anything to do with other methods (e. g. fossils and radiometric dating). The reconstructed history of events forms a "relative time scale", because it is possible to tell that event A occurred prior to event B, which occurred prior to event C, regardless of the actual duration of time between them. Sometimes this study is referred to as "event stratigraphy", a term that applies regardless of the type of event that occurs (biologic, sedimentologic, environmental, volcanic, magnetic, diagenetic, tectonic, etc.).

These simple techniques have widely and successfully applied since at least the early 1700s, and by the early 1800s, geologists had recognized that many obvious similarities existed in terms of the independently-reconstructed sequence of geologic events observed in different parts of the world. One of the earliest (1759) relative time scales based upon this observation was the subdivision of the Earth's stratigraphy (and therefore its history), into the "Primary", "Secondary", "Tertiary", and later (1854) "Quaternary" strata based mainly on characteristic rock types in Europe. The latter two subdivisions, in an emended form, are still used today by geologists. The earliest, "Primary" is somewhat similar to the modern Paleozoic and Precambrian, and the "Secondary" is similar to the modern Mesozoic. Another observation was the similarity of the fossils observed within the succession of strata, which leads to the next topic.

As geologists continued to reconstruct the Earth's geologic history in the 1700s and early 1800s, they quickly recognized that the distribution of fossils within this history was not random -- fossils occurred in a consistent order. This was true at a regional, and even a global scale. Furthermore, fossil organisms were more unique than rock types, and much more varied, offering the potential for a much more precise subdivision of the stratigraphy and events within it.

The recognition of the utility of fossils for more precise "relative dating" is often attributed to William Smith, a canal engineer who observed the fossil succession while digging through the rocks of southern England. But scientists like Albert Oppel hit upon the same principles at about about the same time or earlier. In Smith's case, by using empirical observations of the fossil succession, he was able to propose a fine subdivision of the rocks and map out the formations of southern England in one of the earliest geological maps (1815). Other workers in the rest of Europe, and eventually the rest of the world, were able to compare directly to the same fossil succession in their areas, even when the rock types themselves varied at finer scale. For example, everywhere in the world, trilobites were found lower in the stratigraphy than marine reptiles. Dinosaurs were found after the first occurrence of land plants, insects, and amphibians. Spore-bearing land plants like ferns were always found before the occurrence of flowering plants. And so on.

The observation that fossils occur in a consistent succession is known as the "principle of faunal (and floral) succession". The study of the succession of fossils and its application to relative dating is known as "biostratigraphy". Each increment of time in the stratigraphy could be characterized by a particular assemblage of fossil organisms, formally termed a biostratigraphic "zone" by the German paleontologists Friedrich Quenstedt and Albert Oppel. These zones could then be traced over large regions, and eventually globally. Groups of zones were used to establish larger intervals of stratigraphy, known as geologic "stages" and geologic "systems". The time corresponding to most of these intervals of rock became known as geologic "ages" and "periods", respectively. By the end of the 1830s, most of the presently-used geologic periods had been established based on their fossil content and their observed relative position in the stratigraphy (e. g. Cambrian (1835), Ordovician (1879), Silurian (1835), Devonian (1839), Carboniferous (1822), Permian (1841), Triassic (1834), Jurassic (1829), Cretaceous (1823), Tertiary (1759), and Pleistocene (1839)). These terms were preceded by decades by other terms for various geologic subdivisions, and although there was subsequent debate over their exact boundaries (e. g. between the Cambrian and Silurian Periods, which was resolved by proposal of the Ordovician Period between them), the historical descriptions and fossil succession would be easily recognizable today.

By the 1830s, fossil succession had been studied to an increasing degree, such that the broad history of life on Earth was well understood, regardless of the debate over the names applied to portions of it, and where exactly to make the divisions. All paleontologists recognized unmistakable trends in morphology through time in the succession of fossil organisms. This observation led to attempts to explain the fossil succession by various mechanisms. Perhaps the best known example is Darwin's theory of evolution by natural selection. Note that chronologically, fossil succession was well and independently established long before Darwin's evolutionary theory was proposed in 1859. Fossil succession and the geologic time scale are constrained by the observed order of the stratigraphy -- basically geometry -- not by evolutionary theory.

Radiometric Dating: Calibrating the Relative Time Scale

For almost the next 100 years, geologists operated using relative dating methods, both using the basic principles of geology and fossil succession (biostratigraphy). Various attempts were made as far back as the 1700s to scientifically estimate the age of the Earth, and, later, to use this to calibrate the relative time scale to numeric values (refer to "Changing views of the history of the Earth" by Richard Harter and Chris Stassen). Most of the early attempts were based on rates of deposition, erosion, and other geological processes, which yielded uncertain time estimates, but which clearly indicated Earth history was at least 100 million or more years old. A challenge to this interpretation came in the form of Lord Kelvin's (William Thomson's) calculations of the heat flow from the Earth, and the implication this had for the age -- rather than hundreds of millions of years, the Earth could be as young as tens of million of years old. This evaluation was subsequently invalidated by the discovery of radioactivity in the last years of the 19th century, which was an unaccounted for source of heat in Kelvin's original calculations. With it factored in, the Earth could be vastly older. Estimates of the age of the Earth again returned to the prior methods.

The discovery of radioactivity also had another side effect, although it was several more decades before its additional significance to geology became apparent and the techniques became refined. Because of the chemistry of rocks, it was possible to calculate how much radioactive decay had occurred since an appropriate mineral had formed, and how much time had therefore expired, by looking at the ratio between the original radioactive isotope and its product, if the decay rate was known. Many geological complications and measurement difficulties existed, but initial attempts at the method clearly demonstrated that the Earth was very old. In fact, the numbers that became available were significantly older than even some geologists were expecting -- rather than hundreds of millions of years, which was the minimum age expected, the Earth's history was clearly at least billions of years long.

Radiometric dating provides numerical values for the age of an appropriate rock, usually expressed in millions of years. Therefore, by dating a series of rocks in a vertical succession of strata previously recognized with basic geologic principles (see Stratigraphic principles and relative time ), it can provide a numerical calibration for what would otherwise be only an ordering of events -- i. e. relative dating obtained from biostratigraphy (fossils), superpositional relationships, or other techniques. The integration of relative dating and radiometric dating has resulted in a series of increasingly precise "absolute" (i. e. numeric) geologic time scales, starting from about the 1910s to 1930s (simple radioisotope estimates) and becoming more precise as the modern radiometric dating methods were employed (starting in about the 1950s). 1

A Theoretical Example

To show how relative dating and numeric/absolute dating methods are integrated, it is useful to examine a theoretical example first. Given the background above, the information used for a geologic time scale can be related like this:

Figure 2. How relative dating of events and radiometric (numeric) dates are combined to produce a calibrated geological time scale. In this example, the data demonstrates that "fossil B time" was somewhere between 151 and 140 million years ago, and that "fossil A time" is older than 151 million years ago. Note that because of the position of the dated beds, there is room for improvement in the time constraints on these fossil-bearing intervals (e. g. you could look for a datable volcanic ash at 40-45m to better constrain the time of first appearance of fossil B).

A continuous vertical stratigraphic section will provide the order of occurrence of events (column 1 of Figure 2 ). These are summarized in terms of a "relative time scale" (column 2 of Figure 2 ). Geologists can refer to intervals of time as being "pre-first appearance of species A" or "during the existence of species A", or "after volcanic eruption #1" (at least six subdivisions are possible in the example in Figure 2 ). For this type of "relative dating" to work it must be known that the succession of events is unique (or at least that duplicate events are recognized -- e. g. the "first ash bed" and "second ash bed") and roughly synchronous over the area of interest. Unique events can be biological (e. g. the first appearance of a particular species of organisms) or non-biological (e. g. the deposition of a volcanic ash with a unique chemistry and mineralogy over a wide area), and they will have varying degrees of lateral extent. Ideally, geologists are looking for events that are unmistakably unique, in a consistent order, and of global extent in order to construct a geological time scale with global significance. Some of these events do exist. For example, the boundary between the Cretaceous and Tertiary periods is recognized on the basis of the extinction of a large number of organisms globally (including ammonites, dinosaurs, and others), the first appearance of new types of organisms, the presence of geochemical anomalies (notably iridium), and unusual types of minerals related to meteorite impact processes (impact spherules and shocked quartz). These types of distinctive events provide confirmation that the Earth's stratigraphy is genuinely successional on a global scale. Even without that knowledge, it is still possible to construct local geologic time scales.

Although the idea that unique physical and biotic events are synchronous might sound like an "assumption", it is not. It can, and has been, tested in innumerable ways since the 19th century, in some cases by physically tracing distinct units laterally for hundreds or thousands of kilometres and looking very carefully to see if the order of events changes. Geologists do sometimes find events that are "diachronous" (i. e. not the same age everywhere), but despite this deserved caution, after extensive testing, it is obvious that many events really are synchronous to the limits of resolution offered by the geological record.

Because any newly-studied locality will have independent fossil, superpositional, or radiometric data that have not yet been incorporated into the global geological time scale, all data types serve as both an independent test of each other (on a local scale), and of the global geological time scale itself. The test is more than just a "right" or "wrong" assessment, because there is a certain level of uncertainty in all age determinations. For example, an inconsistency may indicate that a particular geological boundary occurred 76 million years ago, rather than 75 million years ago, which might be cause for revising the age estimate, but does not make the original estimate flagrantly "wrong". It depends upon the exact situation, and how much data are present to test hypotheses (e. g. could the range of a fossil be a bit different from what was thought previously, or could the boundary between two time periods be a slightly different numerical age?). Whatever the situation, the current global geological time scale makes predictions about relationships between relative and absolute age-dating at a local scale, and the input of new data means the global geologic time scale is continually refined and is known with increasing precision. This trend can be seen by looking at the history of proposed geologic time scales (described in the first chapter of [Harland et al, 1982, p.4-5]. and see below).

Circularity?

The unfortunate part of the natural process of refinement of time scales is the appearance of circularity if people do not look at the source of the data carefully enough. Most commonly, this is characterised by oversimplified statements like:

"The fossils date the rock, and the rock dates the fossils."

Even some geologists have stated this misconception (in slightly different words) in seemingly authoritative works (e. g. Rastall, 1956 ), so it is persistent, even if it is categorically wrong (refer to Harper (1980). p.246-247 for a thorough debunking, although it is a rather technical explanation).

When a geologist collects a rock sample for radiometric age dating, or collects a fossil, there are independent constraints on the relative and numerical age of the resulting data. Stratigraphic position is an obvious one, but there are many others. There is no way for a geologist to choose what numerical value a radiometric date will yield, or what position a fossil will be found at in a stratigraphic section. Every piece of data collected like this is an independent check of what has been previously studied. The data are determined by the rocks . not by preconceived notions about what will be found. Every time a rock is picked up it is a test of the predictions made by the current understanding of the geological time scale. The time scale is refined to reflect the relatively few and progressively smaller inconsistencies that are found. This is not circularity, it is the normal scientific process of refining one's understanding with new data. It happens in all sciences.

If an inconsistent data point is found, geologists ask the question: "Is this date wrong, or is it saying the current geological time scale is wrong?" In general, the former is more likely, because there is such a vast amount of data behind the current understanding of the time scale, and because every rock is not expected to preserve an isotopic system for millions of years. However, this statistical likelihood is not assumed, it is tested . usually by using other methods (e. g. other radiometric dating methods or other types of fossils), by re-examining the inconsistent data in more detail, recollecting better quality samples, or running them in the lab again. Geologists search for an explanation of the inconsistency, and will not arbitrarily decide that, "because it conflicts, the data must be wrong."

If it is a small but significant inconsistency, it could indicate that the geological time scale requires a small revision. This happens regularly. The continued revision of the time scale as a result of new data demonstrates that geologists are willing to question it and change it. The geological time scale is far from dogma.

If the new data have a large inconsistency (by "large" I mean orders of magnitude), it is far more likely to be a problem with the new data, but geologists are not satisfied until a specific geological explanation is found and tested. An inconsistency often means something geologically interesting is happening, and there is always a tiny possibility that it could be the tip of a revolution in understanding about geological history. Admittedly, this latter possibility is VERY unlikely. There is almost zero chance that the broad understanding of geological history (e. g. that the Earth is billions of years old) will change. The amount of data supporting that interpretation is immense, is derived from many fields and methods (not only radiometric dating), and a discovery would have to be found that invalidated practically all previous data in order for the interpretation to change greatly. So far, I know of no valid theory that explains how this could occur, let alone evidence in support of such a theory, although there have been highly fallacious attempts (e. g. the classic "moon dust". "decay of the Earth's magnetic field" and "salt in the oceans" claims).

Specific Examples: When Radiometric Dating "Just Works" (or not)

A poor example

There are many situations where radiometric dating is not possible, or where a dating attempt will be fraught with difficulty. This is the inevitable nature of rocks that have experienced millions of years of history: not all of them will preserve their age of origin intact, not every rock will have appropriate chemistry and mineralogy, no sample is perfect, and there is no dating method that can effectively date rocks of any age or rock type. For example, methods with very slow decay rates will be poor for extremely young rocks, and rocks that are low in potassium (K) will be inappropriate for K/Ar dating. The real question is what happens when conditions are ideal, versus when they are marginal, because ideal samples should give the most reliable dates. If there are good reasons to expect problems with a sample, it is hardly surprising if there are!

For example, in the "Dating Game" appendix of his "Bones of Contention" book (1992). Marvin Lubenow provided an example of what happens when a geologically complicated sample is dated -- it can be very difficult to analyze. He discussed the "KBS tuff" near Lake Turkana in Africa, which is a redeposited volcanic ash. It contains a mixture of minerals from a volcanic eruption and detrital mineral grains eroded from other, older rocks. It is also a comparatively "young" sample, approaching the practical limit of the radiometric methods employed (conventional K/Ar dating), particularly at the time of the initial dating attempts in 1969. If the age of this unit were not so crucial to important associated hominid fossils, it probably would not have been dated at all because of the potential problems. After some initial and prolonged troubles over many years, the bed was eventually dated successfully by careful sample preparation that eliminated the detrital minerals. Lubenow's work is fairly unique in characterising the normal scientific process of refining a difficult date as an arbitrary and inappropriate "game", and documenting the history of the process in some detail, as if such problems were typical. Another example is "John Woodmorappe's" paper on radiometric dating (1979). which adopts a "compilation" approach, and gives only superficial treatment to the individual dates. Among other problems documented in an FAQ by Steven Schimmrich. many of Woodmorappe's examples neglect the geological complexities that are expected to cause problems for some radiometrically-dated samples.

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