Dating радио

I. The Radiocarbon Revolution

Since its development by Willard Libby in the 1940s, radiocarbon (14C) dating has become one of the most essential tools in archaeology. Radiocarbon dating was the first chronometric technique widely available to archaeologists and was especially useful because it allowed researchers to directly date the panoply of organic remains often found in archaeological sites including artifacts made from bone, shell, wood, and other carbon based materials. In contrast to relative dating techniques whereby artifacts were simply designated as "older" or "younger" than other cultural remains based on the presence of fossils or stratigraphic position, 14C dating provided an easy and increasingly accessible way for archaeologists to construct chronologies of human behavior and examine temporal changes through time at a finer scale than what had previously been possible. The application of Accelerator Mass Spectrometry (AMS) for radiocarbon dating in the late 1970s was also a major achievement. Compared to conventional radiocarbon techniques such as Libby's solid carbon counting, the gas counting method popular in the mid-1950s, or liquid scintillation (LS) counting, AMS permitted the dating of much smaller sized samples with even greater precision.

Regardless of the particular 14C technique used, the value of this tool for archaeology has clearly been appreciated. Desmond Clark (1979:7) observed that without radiocarbon dating "we would still be foundering in a sea of imprecisions sometime bred of inspired guesswork but more often of imaginative speculation." And as Colin Renfrew (1973) aptly noted over 30 years ago, the "Radiocarbon Revolution" transformed how archaeologists could interpret the past and track cultural changes through a period in human history where we see among other things the massive migration of peoples settling virtually every major region of the world, the transition from hunting and gathering to more intensive forms of food production, and the rise of city-states.

However, as with any dating technique there are limits to the kinds of things that can be satisfactorily dated, levels of precision and accuracy, age range constraints, and different levels of susceptibility to contamination. Radiocarbon dating is especially good for determining the age of sites occupied within the last 26,000 years or so (but has the potential for sites over 50,000), can be used on carbon-based materials (organic or inorganic), and can be accurate to within ±30-50 years. Probably the most important factor to consider when using radiocarbon dating is if external factors, whether through artificial contamination, animal disturbance, or human negligence, contributed to any errors in the determinations. For example, rootlet intrusion, soil type (e. g. limestone carbonates), and handling of the specimens in the field or lab (e. g. accidental introduction of tobacco ash, hair, or fibers) can all potentially affect the age of a sample. Bioturbation by crabs, rodents, and other animals can also cause samples to move between strata leading to age reversals. Shell may succumb to isotopic exchange if it interacts with carbon from percolating ground acids or recrystallization when shell aragonite transforms to calcite and involves the exchange of modern calcite.

The surrounding environment can also influence radiocarbon ages. The introduction of "old" or "artificial" carbon into the atmosphere (i. e. the "Suess Effect" and "Atom Bomb Effect", respectively) can influence the ages of dates making them appear older or younger than they actually are. This is a major concern for bone dates where pretreatment procedures must be employed to isolate protein or a specific amino acid such as hydroxyproline (known to occur almost exclusively in bone collagen) to ensure accurate age assessments of bone specimens. Alone, or in concert, these factors can lead to inaccuracies and misinterpretations by archaeologists without proper investigation of the potential problems associated with sampling and dating.

To help resolve these issues, radiocarbon laboratories have conducted inter-laboratory comparison exercises (see for example, the August 2003 special issue of Radiocarbon), devised rigorous pretreatment procedures to remove any carbon-containing compounds unrelated to the actual sample being dated, and developed calibration methods for terrestrial and marine carbon. Shells of known age collected prior to nuclear testing have also been dated (http://radiocarbon. pa. qub. ac. uk/marine ) to ascertain the effects of old carbon (i. e. local marine reservoir effects).

II. What can we date with radiocarbon dating?

Radiocarbon dating can be used on either organic or inorganic carbonate materials. However, the most common materials dated by archaeologists are wood charcoal, shell, and bone. Radiocarbon analyses are carried out at specialized laboratories around the world (see a list of labs at: http://www. radiocarbon. org/Info/index. html#labs ).

III. How do we measure 14C?

In brief, radiocarbon dating measures the amount of radioactive carbon 14 (14C) in a sample. When a biological organism dies, the radioactive carbon in its body begins to break down or decay. This process of decay occurs at a regular rate and can be measured. By comparing the amount of carbon 14 remaining in a sample with a modern standard, we can determine when the organism died, as for example, when a shellfish was collected or a tree cut down.

However, there are a number of other factors that can affect the amount of carbon present in a sample and how that information is interpreted by archaeologists. Thus a great deal of care is taken in securing and processing samples and multiple samples are often required if we want to be confident about assigning a date to a site, feature, or artifact (read more about the radiocarbon dating technique at: http://www. c14dating. com/int. html ).

In addition, click here to see short movie clips on how radiocarbon is produced in the atmosphere, a decay profile, and how it is analyzed by a lab:

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Radiometric dating

Radiometric dating (often called radioactive dating ) is a technique used to date materials such as rocks or carbon, usually based on a comparison between the observed abundance of a naturally occurring radioactive isotope and its decay products, using known decay rates. [ 1 ] The use of radiometric dating was first published in 1907 by Bertram Boltwood [ 2 ] and is now the principal source of information about the absolute age of rocks and other geological features, including the age of the Earth itself, and can be used to date a wide range of natural and man-made materials. Together with stratigraphic principles. radiometric dating methods are used in geochronology to establish the geological time scale. [ 3 ] Among the best-known techniques are radiocarbon dating. potassium-argon dating and uranium-lead dating. By allowing the establishment of geological timescales, it provides a significant source of information about the ages of fossils and the deduced rates of evolutionary change. Radiometric dating is also used to date archaeological materials, including ancient artifacts.

Different methods of radiometric dating vary in the timescale over which they are accurate and the materials to which they can be applied.

Radioactive decay [ edit ]

Example of a radioactive decay chain from lead-212 ( 212 Pb) to lead-208 ( 208 Pb). Each parent nuclide spontaneously decays into a daughter nuclide (the decay product ) via an ? decay or a ? ? decay. The final decay product, lead-208 ( 208 Pb), is stable and can no longer undergo spontaneous radioactive decay.

All ordinary matter is made up of combinations of chemical elements. each with its own atomic number. indicating the number of protons in the atomic nucleus. Additionally, elements may exist in different isotopes. with each isotope of an element differing in the number of neutrons in the nucleus. A particular isotope of a particular element is called a nuclide. Some nuclides are inherently unstable. That is, at some point in time, an atom of such a nuclide will undergo radioactive decay and spontaneously transform into a different nuclide. This transformation may be accomplished in a number of different ways, including alpha decay (emission of alpha particles ) and beta decay (electron emission, positron emission, or electron capture ). Another possibility is spontaneous fission into two or more nuclides.

For most radioactive nuclides, the half-life depends solely on nuclear properties and is essentially a constant. It is not affected by external factors such as temperature. pressure. chemical environment, or presence of a magnetic or electric field. [ 4 ] [ 5 ] [ 6 ] The only exceptions are nuclides that decay by the process of electron capture. such as beryllium-7. strontium-85. and zirconium-89. whose decay rate may be affected by local electron density. For all other nuclides, the proportion of the original nuclide to its decay products changes in a predictable way as the original nuclide decays over time. This predictability allows the relative abundances of related nuclides to be used as a clock to measure the time from the incorporation of the original nuclides into a material to the present.

GeekWire Radio: The story of Siren, the new dating app that empowers women

We delve into the world of modern dating this week with our guest, Susie Lee, creator of the new app Siren for the iPhone, which aims to improve the dating experience by empowering women to decide who can see their profile and interact with them.

Susie Lee of the Siren dating app in the KIRO studios. (Erynn Rose Photo)

Lee, a contemporary digital artist, came up with the idea for Siren after getting a smartphone and realizing that existing dating apps didn’t facilitate the type of “unexpected and constructive flirting” that can often lead to successful matches in the real world. Features of Siren include a “Question of the Day” designed to elicit responses that shed light on users’ personalities more effectively than filling out a profile page.

“Think about the dynamic between a man and a woman when they first have chemistry,” explains Lee. “She can give you the signals that she’s actually interested in talking with you.” That’s what Siren is aiming to recreate in the new app.

The app is free to download, but you’ll need an invite code that you can request from Lee at susie@siren. mobi. An Android version is set to debut in October.

The conversation with Lee begins in the second segment of the show, at 9:30. Listen via this MP3 file or the audio player below. We also explain why the picture of Lee in this post is in black and white, and how that relates to the app.

The show begins with our weekly news roundup, as GeekWire’s John Cook calls in with a report from Portland’s TechFestNW. We also talk about Seattle’s efforts to attract a big tech company to the Yesler Terrace redevelopment .

Plus, the answer to last week’s Name that Tech Tune challenge and an App of the Week created by Tom Hanks .

GeekWire airs on KIRO Radio in Seattle (97.3 FM) at 7 p. m. Saturdays and 1 p. m. Sundays, except when pre-empted by live sports. The show runs every weekend on GeekWire. com. Get every episode using this RSS feed. or subscribe in iTunes . Also find us on SoundCloud and Stitcher .

Todd Bishop is GeekWire's co-founder and editor, covering subjects including smartphones, tablets, PCs, video games, and tech giants such as Amazon, Apple, Microsoft and Google. Follow him @toddbishop and email todd@geekwire. com .

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