The Borremose bodies are three bog bodies that were found in the Borremose peat bog in Himmerland , Denmark . Recovered between 1946 and 1948, the bodies of a man and two women have been dated to the Nordic Bronze Age . In 1891, the Gundestrup cauldron was found in a nearby bog.
124-504: In 1946, Borremose man was discovered by peat diggers in the southernmost part of the Borremose peat bog. First thought to be a murder victim, the body was later determined to be a bog body. The body was found a half metre down beneath a layer of birch sticks. The body was naked and two sheepskin coats and a woven cap lay beside it. Forensic analysis estimated the man's height at 1.55 m (5 ft 1 in) and carbon dating placed
248-422: A beta particle (an electron , e ) and an electron antineutrino ( ν e ), one of the neutrons in the C nucleus changes to a proton and the C nucleus reverts to the stable (non-radioactive) isotope N . During its life, a plant or animal is in equilibrium with its surroundings by exchanging carbon either with the atmosphere or through its diet. It will, therefore, have
372-435: A boundary marked in most places by a temperature inversion (i.e. a layer of relatively warm air above a colder one), and in others by a zone that is isothermal with height. Although variations do occur, the temperature usually declines with increasing altitude in the troposphere because the troposphere is mostly heated through energy transfer from the surface. Thus, the lowest part of the troposphere (i.e. Earth's surface)
496-527: A decade. It was revised again in the early 1960s to 5,730 ± 40 years, which meant that many calculated dates in papers published prior to this were incorrect (the error in the half-life is about 3%). For consistency with these early papers, it was agreed at the 1962 Radiocarbon Conference in Cambridge (UK) to use the "Libby half-life" of 5568 years. Radiocarbon ages are still calculated using this half-life, and are known as "Conventional Radiocarbon Age". Since
620-505: A factor of 1/ e (0.368) every 7.64 km (25,100 ft), (this is called the scale height ) -- for altitudes out to around 70 km (43 mi; 230,000 ft). However, the atmosphere is more accurately modeled with a customized equation for each layer that takes gradients of temperature, molecular composition, solar radiation and gravity into account. At heights over 100 km, an atmosphere may no longer be well mixed. Then each chemical species has its own scale height. In summary,
744-423: A few years, but the surface waters also receive water from the deep ocean, which has more than 90% of the carbon in the reservoir. Water in the deep ocean takes about 1,000 years to circulate back through surface waters, and so the surface waters contain a combination of older water, with depleted C , and water recently at the surface, with C in equilibrium with the atmosphere. Creatures living at
868-442: A fragment of bone, provides information that can be used to calculate when the animal or plant died. The older a sample is, the less C there is to be detected, and because the half-life of C (the period of time after which half of a given sample will have decayed) is about 5,730 years, the oldest dates that can be reliably measured by this process date to approximately 50,000 years ago (in this interval about 99.8% of
992-408: A given sample stopped exchanging carbon – the older the sample, the less C will be left. The equation governing the decay of a radioactive isotope is: N = N 0 e − λ t {\displaystyle N=N_{0}\,e^{-\lambda t}\,} where N 0 is the number of atoms of the isotope in the original sample (at time t = 0, when
1116-400: A higher δ C than one that eats food with lower δ C values. The animal's own biochemical processes can also impact the results: for example, both bone minerals and bone collagen typically have a higher concentration of C than is found in the animal's diet, though for different biochemical reasons. The enrichment of bone C also implies that excreted material
1240-514: A layer in which temperatures rise with increasing altitude. This rise in temperature is caused by the absorption of ultraviolet radiation (UV) from the Sun by the ozone layer, which restricts turbulence and mixing. Although the temperature may be −60 °C (−76 °F; 210 K) at the tropopause, the top of the stratosphere is much warmer, and may be near 0 °C. The stratospheric temperature profile creates very stable atmospheric conditions, so
1364-574: A mass of about 5.15 × 10 kg, three quarters of which is within about 11 km (6.8 mi; 36,000 ft) of the surface. The atmosphere becomes thinner with increasing altitude, with no definite boundary between the atmosphere and outer space . The Kármán line , at 100 km (62 mi) or 1.57% of Earth's radius, is often used as the border between the atmosphere and outer space. Atmospheric effects become noticeable during atmospheric reentry of spacecraft at an altitude of around 120 km (75 mi). Several layers can be distinguished in
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#17327976805621488-413: A mass of less than 1% of those on land and are not shown in the diagram. Accumulated dead organic matter, of both plants and animals, exceeds the mass of the biosphere by a factor of nearly 3, and since this matter is no longer exchanging carbon with its environment, it has a C / C ratio lower than that of the biosphere. The variation in the C / C ratio in different parts of
1612-617: A method for determining the age of an object containing organic material by using the properties of radiocarbon , a radioactive isotope of carbon . The method was developed in the late 1940s at the University of Chicago by Willard Libby , based on the constant creation of radiocarbon ( C ) in the Earth's atmosphere by the interaction of cosmic rays with atmospheric nitrogen . The resulting C combines with atmospheric oxygen to form radioactive carbon dioxide , which
1736-485: A million miles away, were found to be reflected light from ice crystals in the atmosphere. When light passes through Earth's atmosphere, photons interact with it through scattering . If the light does not interact with the atmosphere, it is called direct radiation and is what you see if you were to look directly at the Sun. Indirect radiation is light that has been scattered in the atmosphere. For example, on an overcast day when you cannot see your shadow, there
1860-641: A month and requires a sample about ten times as large as would be needed otherwise, but it allows more precise measurement of the C / C ratio in old material and extends the maximum age that can be reliably reported. Atmosphere of Earth The atmosphere of Earth is composed of a layer of gas mixture that surrounds the Earth 's planetary surface (both lands and oceans ), known collectively as air , with variable quantities of suspended aerosols and particulates (which create weather features such as clouds and hazes ), all retained by Earth's gravity . The atmosphere serves as
1984-869: A paper in Science in 1947, in which the authors commented that their results implied it would be possible to date materials containing carbon of organic origin. Libby and James Arnold proceeded to test the radiocarbon dating theory by analyzing samples with known ages. For example, two samples taken from the tombs of two Egyptian kings, Zoser and Sneferu , independently dated to 2625 BC plus or minus 75 years, were dated by radiocarbon measurement to an average of 2800 BC plus or minus 250 years. These results were published in Science in December 1949. Within 11 years of their announcement, more than 20 radiocarbon dating laboratories had been set up worldwide. In 1960, Libby
2108-737: A protective buffer between the Earth's surface and outer space , shields the surface from most meteoroids and ultraviolet solar radiation , keeps it warm and reduces diurnal temperature variation (temperature extremes between day and night ) through heat retention ( greenhouse effect ), redistributes heat and moisture among different regions via air currents , and provides the chemical and climate conditions allowing life to exist and evolve on Earth. By mole fraction (i.e., by quantity of molecules ), dry air contains 78.08% nitrogen , 20.95% oxygen , 0.93% argon , 0.04% carbon dioxide , and small amounts of other trace gases . Air also contains
2232-629: A sample. More recently, accelerator mass spectrometry has become the method of choice; it counts all the C atoms in the sample and not just the few that happen to decay during the measurements; it can therefore be used with much smaller samples (as small as individual plant seeds), and gives results much more quickly. The development of radiocarbon dating has had a profound impact on archaeology . In addition to permitting more accurate dating within archaeological sites than previous methods, it allows comparison of dates of events across great distances. Histories of archaeology often refer to its impact as
2356-445: A variable amount of water vapor , on average around 1% at sea level, and 0.4% over the entire atmosphere. Air composition, temperature and atmospheric pressure vary with altitude . Within the atmosphere, air suitable for use in photosynthesis by terrestrial plants and respiration of terrestrial animals is found only within 12 kilometres (7.5 mi) from the ground. Earth's early atmosphere consisted of accreted gases from
2480-557: Is 14 °C (57 °F; 287 K) or 15 °C (59 °F; 288 K), depending on the reference. The average atmospheric pressure at sea level is defined by the International Standard Atmosphere as 101325 pascals (760.00 Torr ; 14.6959 psi ; 760.00 mmHg ). This is sometimes referred to as a unit of standard atmospheres (atm) . Total atmospheric mass is 5.1480×10 kg (1.135×10 lb), about 2.5% less than would be inferred from
2604-408: Is about 1.2 kg/m (1.2 g/L, 0.0012 g/cm ). Density is not measured directly but is calculated from measurements of temperature, pressure and humidity using the equation of state for air (a form of the ideal gas law ). Atmospheric density decreases as the altitude increases. This variation can be approximately modeled using the barometric formula . More sophisticated models are used to predict
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#17327976805622728-414: Is about 28.946 or 28.96 g/mol. This is decreased when the air is humid. The relative concentration of gases remains constant until about 10,000 m (33,000 ft). In general, air pressure and density decrease with altitude in the atmosphere. However, temperature has a more complicated profile with altitude and may remain relatively constant or even increase with altitude in some regions (see
2852-429: Is also referred to individually as a carbon exchange reservoir. The different elements of the carbon exchange reservoir vary in how much carbon they store, and in how long it takes for the C generated by cosmic rays to fully mix with them. This affects the ratio of C to C in the different reservoirs, and hence the radiocarbon ages of samples that originated in each reservoir. The atmosphere, which
2976-414: Is assumed to have originally had the same C / C ratio as the ratio in the atmosphere, and since the size of the sample is known, the total number of atoms in the sample can be calculated, yielding N 0 , the number of C atoms in the original sample. Measurement of N , the number of C atoms currently in the sample, allows the calculation of t , the age of the sample, using
3100-442: Is because clouds (H 2 O) are strong absorbers and emitters of infrared radiation. This is also why it becomes colder at night at higher elevations. The greenhouse effect is directly related to this absorption and emission effect. Some gases in the atmosphere absorb and emit infrared radiation, but do not interact with sunlight in the visible spectrum. Common examples of these are CO 2 and H 2 O. The refractive index of air
3224-1429: Is called paleoclimatology . The three major constituents of Earth's atmosphere are nitrogen , oxygen , and argon . Water vapor accounts for roughly 0.25% of the atmosphere by mass. The concentration of water vapor (a greenhouse gas) varies significantly from around 10 ppm by mole fraction in the coldest portions of the atmosphere to as much as 5% by mole fraction in hot, humid air masses, and concentrations of other atmospheric gases are typically quoted in terms of dry air (without water vapor). The remaining gases are often referred to as trace gases, among which are other greenhouse gases , principally carbon dioxide, methane, nitrous oxide, and ozone. Besides argon, other noble gases , neon , helium , krypton , and xenon are also present. Filtered air includes trace amounts of many other chemical compounds . Many substances of natural origin may be present in locally and seasonally variable small amounts as aerosols in an unfiltered air sample, including dust of mineral and organic composition, pollen and spores , sea spray , and volcanic ash . Various industrial pollutants also may be present as gases or aerosols, such as chlorine (elemental or in compounds), fluorine compounds and elemental mercury vapor. Sulfur compounds such as hydrogen sulfide and sulfur dioxide (SO 2 ) may be derived from natural sources or from industrial air pollution. Mole fraction
3348-447: Is close to, but just greater than, 1. Systematic variations in the refractive index can lead to the bending of light rays over long optical paths. One example is that, under some circumstances, observers on board ships can see other vessels just over the horizon because light is refracted in the same direction as the curvature of Earth's surface. The refractive index of air depends on temperature, giving rise to refraction effects when
3472-440: Is contaminated so that 1% of the sample is modern carbon, it will appear to be 600 years younger; for a sample that is 34,000 years old, the same amount of contamination would cause an error of 4,000 years. Contamination with old carbon, with no remaining C , causes an error in the other direction independent of age – a sample contaminated with 1% old carbon will appear to be about 80 years older than it truly is, regardless of
3596-428: Is depleted in C because of the marine effect, C is removed from the southern atmosphere more quickly than in the north. The effect is strengthened by strong upwelling around Antarctica. If the carbon in freshwater is partly acquired from aged carbon, such as rocks, then the result will be a reduction in the C / C ratio in the water. For example, rivers that pass over limestone , which
3720-400: Is depleted in C relative to the diet. Since C makes up about 1% of the carbon in a sample, the C / C ratio can be accurately measured by mass spectrometry . Typical values of δ C have been found by experiment for many plants, as well as for different parts of animals such as bone collagen , but when dating a given sample it is better to determine
3844-426: Is done by calibration curves (discussed below), which convert a measurement of C in a sample into an estimated calendar age. The calculations involve several steps and include an intermediate value called the "radiocarbon age", which is the age in "radiocarbon years" of the sample: an age quoted in radiocarbon years means that no calibration curve has been used − the calculations for radiocarbon years assume that
Borremose bodies - Misplaced Pages Continue
3968-409: Is incorporated into plants by photosynthesis ; animals then acquire C by eating the plants. When the animal or plant dies, it stops exchanging carbon with its environment, and thereafter the amount of C it contains begins to decrease as the C undergoes radioactive decay . Measuring the proportion of C in a sample from a dead plant or animal, such as a piece of wood or
4092-459: Is less CO 2 available for the photosynthetic reactions. Under these conditions, fractionation is reduced, and at temperatures above 14 °C (57 °F) the δ C values are correspondingly higher, while at lower temperatures, CO 2 becomes more soluble and hence more available to marine organisms. The δ C value for animals depends on their diet. An animal that eats food with high δ C values will have
4216-477: Is mainly composed of extremely low densities of hydrogen, helium and several heavier molecules including nitrogen, oxygen and carbon dioxide closer to the exobase. The atoms and molecules are so far apart that they can travel hundreds of kilometres without colliding with one another. Thus, the exosphere no longer behaves like a gas, and the particles constantly escape into space . These free-moving particles follow ballistic trajectories and may migrate in and out of
4340-415: Is mostly composed of calcium carbonate , will acquire carbonate ions. Similarly, groundwater can contain carbon derived from the rocks through which it has passed. These rocks are usually so old that they no longer contain any measurable C , so this carbon lowers the C / C ratio of the water it enters, which can lead to apparent ages of thousands of years for both the affected water and
4464-445: Is no direct radiation reaching you, it has all been scattered. As another example, due to a phenomenon called Rayleigh scattering , shorter (blue) wavelengths scatter more easily than longer (red) wavelengths. This is why the sky looks blue; you are seeing scattered blue light. This is also why sunsets are red. Because the Sun is close to the horizon, the Sun's rays pass through more atmosphere than normal before reaching your eye. Much of
4588-419: Is now used to convert a given measurement of radiocarbon in a sample into an estimate of the sample's calendar age. Other corrections must be made to account for the proportion of C in different types of organisms (fractionation), and the varying levels of C throughout the biosphere (reservoir effects). Additional complications come from the burning of fossil fuels such as coal and oil, and from
4712-513: Is so tenuous that some scientists consider it to be part of interplanetary space rather than part of the atmosphere). It extends from the thermopause (also known as the "exobase") at the top of the thermosphere to a poorly defined boundary with the solar wind and interplanetary medium . The altitude of the exobase varies from about 500 kilometres (310 mi; 1,600,000 ft) to about 1,000 kilometres (620 mi) in times of higher incoming solar radiation. The upper limit varies depending on
4836-456: Is sometimes called) percolates into the rest of the reservoir. Photosynthesis is the primary process by which carbon moves from the atmosphere into living things. In photosynthetic pathways C is absorbed slightly more easily than C , which in turn is more easily absorbed than C . The differential uptake of the three carbon isotopes leads to C / C and C / C ratios in plants that differ from
4960-481: Is sometimes referred to as volume fraction ; these are identical for an ideal gas only. ppm: parts per million by molecular count The concentration of CO 2 has been increasing in recent decades , as has that of CH 4 . Water vapor is about 0.25% by mass over full atmosphere Water vapor varies significantly locally The average molecular weight of dry air, which can be used to calculate densities or to convert between mole fraction and mass fraction,
5084-461: Is the lowest layer of Earth's atmosphere. It extends from Earth's surface to an average height of about 12 km (7.5 mi; 39,000 ft), although this altitude varies from about 9 km (5.6 mi; 30,000 ft) at the geographic poles to 17 km (11 mi; 56,000 ft) at the Equator , with some variation due to weather. The troposphere is bounded above by the tropopause ,
Borremose bodies - Misplaced Pages Continue
5208-453: Is the main pathway by which C is created: n + 7 N → 6 C + p where n represents a neutron and p represents a proton . Once produced, the C quickly combines with the oxygen ( O ) in the atmosphere to form first carbon monoxide ( CO ), and ultimately carbon dioxide ( CO 2 ). C + O 2 → CO + O CO + OH → CO 2 + H Carbon dioxide produced in this way diffuses in
5332-412: Is too low to conduct a significant amount of energy to or from the skin. This layer is completely cloudless and free of water vapor. However, non-hydrometeorological phenomena such as the aurora borealis and aurora australis are occasionally seen in the thermosphere. The International Space Station orbits in this layer, between 350 and 420 km (220 and 260 mi). It is this layer where many of
5456-479: Is typically the warmest section of the troposphere. This promotes vertical mixing (hence, the origin of its name in the Greek word τρόπος, tropos , meaning "turn"). The troposphere contains roughly 80% of the mass of Earth's atmosphere. The troposphere is denser than all its overlying layers because a larger atmospheric weight sits on top of the troposphere and causes it to be most severely compressed. Fifty percent of
5580-565: Is usually needed to determine the size of the offset, for example by comparing the radiocarbon age of deposited freshwater shells with associated organic material. Volcanic eruptions eject large amounts of carbon into the air. The carbon is of geological origin and has no detectable C , so the C / C ratio in the vicinity of the volcano is depressed relative to surrounding areas. Dormant volcanoes can also emit aged carbon. Plants that photosynthesize this carbon also have lower C / C ratios: for example, plants in
5704-399: Is where C is generated, contains about 1.9% of the total carbon in the reservoirs, and the C it contains mixes in less than seven years. The ratio of C to C in the atmosphere is taken as the baseline for the other reservoirs: if another reservoir has a lower ratio of C to C , it indicates that the carbon is older and hence that either some of
5828-402: The C has decayed, or the reservoir is receiving carbon that is not at the atmospheric baseline. The ocean surface is an example: it contains 2.4% of the carbon in the exchange reservoir, but there is only about 95% as much C as would be expected if the ratio were the same as in the atmosphere. The time it takes for carbon from the atmosphere to mix with the surface ocean is only
5952-526: The C will have decayed), although special preparation methods occasionally make an accurate analysis of older samples possible. In 1960, Libby received the Nobel Prize in Chemistry for his work. Research has been ongoing since the 1960s to determine what the proportion of C in the atmosphere has been over the past 50,000 years. The resulting data, in the form of a calibration curve ,
6076-489: The C / C ratio in the atmosphere. This increase in C concentration almost exactly cancels out the decrease caused by the upwelling of water (containing old, and hence C -depleted, carbon) from the deep ocean, so that direct measurements of C radiation are similar to measurements for the rest of the biosphere. Correcting for isotopic fractionation, as is done for all radiocarbon dates to allow comparison between results from different parts of
6200-404: The δ C value for that sample directly than to rely on the published values. The carbon exchange between atmospheric CO 2 and carbonate at the ocean surface is also subject to fractionation, with C in the atmosphere more likely than C to dissolve in the ocean. The result is an overall increase in the C / C ratio in the ocean of 1.5%, relative to
6324-582: The F-layer of the ionosphere where they encounter enough atmospheric drag to require reboosts every few months, otherwise, orbital decay will occur resulting in a return to Earth. Depending on solar activity, satellites can experience noticeable atmospheric drag at altitudes as high as 700–800 km. The division of the atmosphere into layers mostly by reference to temperature is discussed above. Temperature decreases with altitude starting at sea level, but variations in this trend begin above 11 km, where
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#17327976805626448-588: The infrared to around 1100 nm. There are also infrared and radio windows that transmit some infrared and radio waves at longer wavelengths. For example, the radio window runs from about one centimetre to about eleven-metre waves. Emission is the opposite of absorption, it is when an object emits radiation. Objects tend to emit amounts and wavelengths of radiation depending on their " black body " emission curves, therefore hotter objects tend to emit more radiation, with shorter wavelengths. Colder objects emit less radiation, with longer wavelengths. For example,
6572-433: The magnetosphere or the solar wind. Every second, the Earth loses about 3 kg of hydrogen, 50 g of helium, and much smaller amounts of other constituents. The exosphere is too far above Earth for meteorological phenomena to be possible. However, Earth's auroras —the aurora borealis (northern lights) and aurora australis (southern lights)—sometimes occur in the lower part of the exosphere, where they overlap into
6696-402: The mesopause that marks the top of this middle layer of the atmosphere. It is the coldest place on Earth and has an average temperature around −85 °C (−120 °F ; 190 K ). Just below the mesopause, the air is so cold that even the very scarce water vapor at this altitude can condense into polar-mesospheric noctilucent clouds of ice particles. These are the highest clouds in
6820-451: The solar nebula , but the atmosphere changed significantly over time, affected by many factors such as volcanism , impact events , weathering and the evolution of life (particularly the photoautotrophs ). Recently, human activity has also contributed to atmospheric changes , such as climate change (mainly through deforestation and fossil fuel -related global warming ), ozone depletion and acid deposition . The atmosphere has
6944-428: The temperature section). Because the general pattern of the temperature/altitude profile, or lapse rate , is constant and measurable by means of instrumented balloon soundings , the temperature behavior provides a useful metric to distinguish atmospheric layers. This atmospheric stratification divides the Earth's atmosphere into five main layers: The exosphere is the outermost layer of Earth's atmosphere (though it
7068-511: The tropopause . This layer extends from the top of the troposphere at roughly 12 km (7.5 mi; 39,000 ft) above Earth's surface to the stratopause at an altitude of about 50 to 55 km (31 to 34 mi; 164,000 to 180,000 ft). The atmospheric pressure at the top of the stratosphere is roughly 1/1000 the pressure at sea level . It contains the ozone layer , which is the part of Earth's atmosphere that contains relatively high concentrations of that gas. The stratosphere defines
7192-677: The "radiocarbon revolution". Radiocarbon dating has allowed key transitions in prehistory to be dated, such as the end of the last ice age , and the beginning of the Neolithic and Bronze Age in different regions. In 1939, Martin Kamen and Samuel Ruben of the Radiation Laboratory at Berkeley began experiments to determine if any of the elements common in organic matter had isotopes with half-lives long enough to be of value in biomedical research. They synthesized C using
7316-573: The Kármán line, significant atmospheric effects such as auroras still occur. Meteors begin to glow in this region, though the larger ones may not burn up until they penetrate more deeply. The various layers of Earth's ionosphere , important to HF radio propagation, begin below 100 km and extend beyond 500 km. By comparison, the International Space Station and Space Shuttle typically orbit at 350–400 km, within
7440-459: The Sun is approximately 6,000 K (5,730 °C ; 10,340 °F ), its radiation peaks near 500 nm, and is visible to the human eye. Earth is approximately 290 K (17 °C; 62 °F), so its radiation peaks near 10,000 nm, and is much too long to be visible to humans. Because of its temperature, the atmosphere emits infrared radiation. For example, on clear nights Earth's surface cools down faster than on cloudy nights. This
7564-399: The above-ground nuclear tests performed in the 1950s and 1960s. Because the time it takes to convert biological materials to fossil fuels is substantially longer than the time it takes for its C to decay below detectable levels, fossil fuels contain almost no C . As a result, beginning in the late 19th century, there was a noticeable drop in the proportion of C in
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#17327976805627688-549: The acidic peat. A leather cord with an amber bead and bronze plate was around the neck. The skull was crushed and the right leg was broken below the knee. The bones of an infant and a ceramic jar were lying nearby. Because the body was largely decayed, further forensic analysis was hampered. Later carbon dating placed the age of the remains to about 400 BCE. 56°47′36″N 9°34′55″E / 56.79333°N 9.58194°E / 56.79333; 9.58194 The body of another woman (known as Borremose III or Borremose Woman )
7812-399: The actual calendar date, both because it uses the wrong value for the half-life of C , and because no correction (calibration) has been applied for the historical variation of C in the atmosphere over time. Carbon is distributed throughout the atmosphere, the biosphere, and the oceans; these are referred to collectively as the carbon exchange reservoir, and each component
7936-404: The age of the body at c. 700 BC. Borremose Man was found with a 36-centimetre (14 in) rope with a slipknot around his neck indicating death by strangulation. However, examination also revealed a crushing blow to the back of the skull and the right femur had been broken. 56°47′23″N 9°34′11″E / 56.78972°N 9.56972°E / 56.78972; 9.56972 In 1947, a body
8060-418: The appropriate correction for the location of their samples. The effect also applies to marine organisms such as shells, and marine mammals such as whales and seals, which have radiocarbon ages that appear to be hundreds of years old. The northern and southern hemispheres have atmospheric circulation systems that are sufficiently independent of each other that there is a noticeable time lag in mixing between
8184-420: The aptly-named thermosphere above 90 km. Because in an ideal gas of constant composition the speed of sound depends only on temperature and not on pressure or density, the speed of sound in the atmosphere with altitude takes on the form of the complicated temperature profile (see illustration to the right), and does not mirror altitudinal changes in density or pressure. The density of air at sea level
8308-421: The atmosphere also cools by emitting radiation, as discussed below. The combined absorption spectra of the gases in the atmosphere leave "windows" of low opacity , allowing the transmission of only certain bands of light. The optical window runs from around 300 nm ( ultraviolet -C) up into the range humans can see, the visible spectrum (commonly called light), at roughly 400–700 nm and continues to
8432-399: The atmosphere and may be visible to the naked eye if sunlight reflects off them about an hour or two after sunset or similarly before sunrise. They are most readily visible when the Sun is around 4 to 16 degrees below the horizon. Lightning-induced discharges known as transient luminous events (TLEs) occasionally form in the mesosphere above tropospheric thunderclouds . The mesosphere is also
8556-457: The atmosphere as the carbon dioxide generated from burning fossil fuels began to accumulate. Conversely, nuclear testing increased the amount of C in the atmosphere, which reached a maximum in about 1965 of almost double the amount present in the atmosphere prior to nuclear testing. Measurement of radiocarbon was originally done with beta-counting devices, which counted the amount of beta radiation emitted by decaying C atoms in
8680-489: The atmosphere based on characteristics such as temperature and composition, namely the troposphere , stratosphere , mesosphere , thermosphere (formally the ionosphere ) and exosphere . The study of Earth's atmosphere and its processes is called atmospheric science (aerology), and includes multiple subfields, such as climatology and atmospheric physics . Early pioneers in the field include Léon Teisserenc de Bort and Richard Assmann . The study of historic atmosphere
8804-438: The atmosphere might be expected to decrease over thousands of years, but C is constantly being produced in the lower stratosphere and upper troposphere , primarily by galactic cosmic rays , and to a lesser degree by solar cosmic rays. These cosmic rays generate neutrons as they travel through the atmosphere which can strike nitrogen-14 ( N ) atoms and turn them into C . The following nuclear reaction
8928-547: The atmosphere, is dissolved in the ocean, and is taken up by plants via photosynthesis . Animals eat the plants, and ultimately the radiocarbon is distributed throughout the biosphere . The ratio of C to C is approximately 1.25 parts of C to 10 parts of C . In addition, about 1% of the carbon atoms are of the stable isotope C . The equation for the radioactive decay of C is: 6 C → 7 N + e + ν e By emitting
9052-421: The atmospheric C / C ratio has not changed over time. Calculating radiocarbon ages also requires the value of the half-life for C . In Libby's 1949 paper he used a value of 5720 ± 47 years, based on research by Engelkemeir et al. This was remarkably close to the modern value, but shortly afterwards the accepted value was revised to 5568 ± 30 years, and this value was in use for more than
9176-637: The average sea level pressure and Earth's area of 51007.2 megahectares, this portion being displaced by Earth's mountainous terrain. Atmospheric pressure is the total weight of the air above unit area at the point where the pressure is measured. Thus air pressure varies with location and weather . If the entire mass of the atmosphere had a uniform density equal to sea level density (about 1.2 kg per m ) from sea level upwards, it would terminate abruptly at an altitude of 8.50 km (27,900 ft). Air pressure actually decreases exponentially with altitude, dropping by half every 5.6 km (18,000 ft) or by
9300-425: The biosphere, gives an apparent age of about 400 years for ocean surface water. Libby's original exchange reservoir hypothesis assumed that the C / C ratio in the exchange reservoir is constant all over the world, but it has since been discovered that there are several causes of variation in the ratio across the reservoir. The CO 2 in the atmosphere transfers to the ocean by dissolving in
9424-414: The blue light has been scattered out, leaving the red light in a sunset. Different molecules absorb different wavelengths of radiation. For example, O 2 and O 3 absorb almost all radiation with wavelengths shorter than 300 nanometres . Water (H 2 O) absorbs at many wavelengths above 700 nm. When a molecule absorbs a photon, it increases the energy of the molecule. This heats the atmosphere, but
9548-454: The calibration curve (IntCal) also reports past atmospheric C concentration using this conventional age, any conventional ages calibrated against the IntCal curve will produce a correct calibrated age. When a date is quoted, the reader should be aware that if it is an uncalibrated date (a term used for dates given in radiocarbon years) it may differ substantially from the best estimate of
9672-435: The carbon exchange reservoir means that a straightforward calculation of the age of a sample based on the amount of C it contains will often give an incorrect result. There are several other possible sources of error that need to be considered. The errors are of four general types: In the early years of using the technique, it was understood that it depended on the atmospheric C / C ratio having remained
9796-500: The carbon exchange reservoir, but because of the long delay in mixing with the deep ocean, the actual effect is a 3% reduction. A much larger effect comes from above-ground nuclear testing, which released large numbers of neutrons into the atmosphere, resulting in the creation of C . From about 1950 until 1963, when atmospheric nuclear testing was banned , it is estimated that several tonnes of C were created. If all this extra C had immediately been spread across
9920-435: The date of the sample. Samples for dating need to be converted into a form suitable for measuring the C content; this can mean conversion to gaseous, liquid, or solid form, depending on the measurement technique to be used. Before this can be done, the sample must be treated to remove any contamination and any unwanted constituents. This includes removing visible contaminants, such as rootlets that may have penetrated
10044-415: The definition. Various authorities consider it to end at about 10,000 kilometres (6,200 mi) or about 190,000 kilometres (120,000 mi)—about halfway to the moon, where the influence of Earth's gravity is about the same as radiation pressure from sunlight. The geocorona visible in the far ultraviolet (caused by neutral hydrogen) extends to at least 100,000 kilometres (62,000 mi). This layer
10168-494: The early 20th century hence gives an apparent date older than the true date. For the same reason, C concentrations in the neighbourhood of large cities are lower than the atmospheric average. This fossil fuel effect (also known as the Suess effect, after Hans Suess, who first reported it in 1955) would only amount to a reduction of 0.2% in C activity if the additional carbon from fossil fuels were distributed throughout
10292-401: The entire carbon exchange reservoir, it would have led to an increase in the C / C ratio of only a few per cent, but the immediate effect was to almost double the amount of C in the atmosphere, with the peak level occurring in 1964 for the northern hemisphere, and in 1966 for the southern hemisphere. The level has since dropped, as this bomb pulse or "bomb carbon" (as it
10416-424: The equation above. The half-life of a radioactive isotope (usually denoted by t 1/2 ) is a more familiar concept than the mean-life, so although the equations above are expressed in terms of the mean-life, it is more usual to quote the value of C 's half-life than its mean-life. The currently accepted value for the half-life of C is 5,700 ± 30 years. This means that after 5,700 years, only half of
10540-471: The errors caused by the variation over time in the C / C ratio. These curves are described in more detail below . Coal and oil began to be burned in large quantities during the 19th century. Both are sufficiently old that they contain little or no detectable C and, as a result, the CO 2 released substantially diluted the atmospheric C / C ratio. Dating an object from
10664-908: The former is much easier to measure, and the latter can be easily derived: the depletion of C relative to C is proportional to the difference in the atomic masses of the two isotopes, so the depletion for C is twice the depletion of C . The fractionation of C , known as δ C , is calculated as follows: δ C 13 = ( ( C 13 C 12 ) sample ( C 13 C 12 ) standard − 1 ) × 1000 {\displaystyle \delta {\ce {^{13}C}}=\left({\frac {\left({\frac {{\ce {^{13}C}}}{{\ce {^{12}C}}}}\right)_{\text{sample}}}{\left({\frac {{\ce {^{13}C}}}{{\ce {^{12}C}}}}\right)_{\text{standard}}}}-1\right)\times 1000} ‰ where
10788-434: The gas molecules are so far apart that its temperature in the usual sense is not very meaningful. The air is so rarefied that an individual molecule (of oxygen , for example) travels an average of 1 kilometre (0.62 mi; 3300 ft) between collisions with other molecules. Although the thermosphere has a high proportion of molecules with high energy, it would not feel hot to a human in direct contact, because its density
10912-454: The initial C will remain; a quarter will remain after 11,400 years; an eighth after 17,100 years; and so on. The above calculations make several assumptions, such as that the level of C in the atmosphere has remained constant over time. In fact, the level of C in the atmosphere has varied significantly and as a result, the values provided by the equation above have to be corrected by using data from other sources. This
11036-404: The inner tree rings do not get their C replenished and instead only lose C through radioactive decay. Hence each ring preserves a record of the atmospheric C / C ratio of the year it grew in. Carbon-dating the wood from the tree rings themselves provides the check needed on the atmospheric C / C ratio: with a sample of known date, and a measurement of
11160-673: The laboratory's cyclotron accelerator and soon discovered that the atom's half-life was far longer than had been previously thought. This was followed by a prediction by Serge A. Korff , then employed at the Franklin Institute in Philadelphia , that the interaction of thermal neutrons with N in the upper atmosphere would create C . It had previously been thought that C would be more likely to be created by deuterons interacting with C . At some time during World War II, Willard Libby , who
11284-403: The layer where most meteors burn up upon atmospheric entrance. It is too high above Earth to be accessible to jet-powered aircraft and balloons, and too low to permit orbital spacecraft. The mesosphere is mainly accessed by sounding rockets and rocket-powered aircraft . The stratosphere is the second-lowest layer of Earth's atmosphere. It lies above the troposphere and is separated from it by
11408-482: The mass of Earth's atmosphere is distributed approximately as follows: By comparison, the summit of Mount Everest is at 8,848 m (29,029 ft); commercial airliners typically cruise between 10 and 13 km (33,000 and 43,000 ft) where the lower density and temperature of the air improve fuel economy; weather balloons reach 30.4 km (100,000 ft) and above; and the highest X-15 flight in 1963 reached 108.0 km (354,300 ft). Even above
11532-612: The neck prevented the detection of strangulation. Re-examination showed that the damage to the skull had happened after death and was caused by demineralization of the bones as well as pressure from the peat. Carbon dating set the body's age to ca. 770 (+/-100) BCE. In 1984, a forensic examination of Borremose Woman was undertaken by Andersen and Geert Inger and Elisabeth Munksgaard of the Natural History Museum in Copenhagen. Their examination confirmed that damage to
11656-510: The neighbourhood of the Furnas caldera in the Azores were found to have apparent ages that ranged from 250 years to 3320 years. Any addition of carbon to a sample of a different age will cause the measured date to be inaccurate. Contamination with modern carbon causes a sample to appear to be younger than it really is: the effect is greater for older samples. If a sample that is 17,000 years old
11780-420: The ocean surface have the same C ratios as the water they live in, and as a result of the reduced C / C ratio, the radiocarbon age of marine life is typically about 400 years. Organisms on land are in closer equilibrium with the atmosphere and have the same C / C ratio as the atmosphere. These organisms contain about 1.3% of the carbon in the reservoir; sea organisms have
11904-514: The orbital decay of satellites. The average mass of the atmosphere is about 5 quadrillion (5 × 10 ) tonnes or 1/1,200,000 the mass of Earth. According to the American National Center for Atmospheric Research , "The total mean mass of the atmosphere is 5.1480 × 10 kg with an annual range due to water vapor of 1.2 or 1.5 × 10 kg, depending on whether surface pressure or water vapor data are used; somewhat smaller than
12028-635: The organism from which the sample was taken died), and N is the number of atoms left after time t . λ is a constant that depends on the particular isotope; for a given isotope it is equal to the reciprocal of the mean-life – i.e. the average or expected time a given atom will survive before undergoing radioactive decay. The mean-life, denoted by τ , of C is 8,267 years, so the equation above can be rewritten as: t = ln ( N 0 / N ) ⋅ 8267 years {\displaystyle t=\ln(N_{0}/N)\cdot {\text{8267 years}}} The sample
12152-440: The plants and freshwater organisms that live in it. This is known as the hard water effect because it is often associated with calcium ions, which are characteristic of hard water; other sources of carbon such as humus can produce similar results, and can also reduce the apparent age if they are of more recent origin than the sample. The effect varies greatly and there is no general offset that can be applied; additional research
12276-413: The pre-existing Egyptian chronology nor the new radiocarbon dating method could be assumed to be accurate, but a third possibility was that the C / C ratio had changed over time. The question was resolved by the study of tree rings : comparison of overlapping series of tree rings allowed the construction of a continuous sequence of tree-ring data that spanned 8,000 years. (Since that time
12400-526: The previous estimate. The mean mass of water vapor is estimated as 1.27 × 10 kg and the dry air mass as 5.1352 ±0.0003 × 10 kg." Solar radiation (or sunlight) is the energy Earth receives from the Sun . Earth also emits radiation back into space, but at longer wavelengths that humans cannot see. Part of the incoming and emitted radiation is absorbed or reflected by the atmosphere. In May 2017, glints of light, seen as twinkling from an orbiting satellite
12524-405: The ratios in the atmosphere. This effect is known as isotopic fractionation. To determine the degree of fractionation that takes place in a given plant, the amounts of both C and C isotopes are measured, and the resulting C / C ratio is then compared to a standard ratio known as PDB. The C / C ratio is used instead of C / C because
12648-415: The same over the preceding few thousand years. To verify the accuracy of the method, several artefacts that were datable by other techniques were tested; the results of the testing were in reasonable agreement with the true ages of the objects. Over time, however, discrepancies began to appear between the known chronology for the oldest Egyptian dynasties and the radiocarbon dates of Egyptian artefacts. Neither
12772-456: The same proportion of C as the atmosphere, or in the case of marine animals or plants, with the ocean. Once it dies, it ceases to acquire C , but the C within its biological material at that time will continue to decay, and so the ratio of C to C in its remains will gradually decrease. Because C decays at a known rate, the proportion of radiocarbon can be used to determine how long it has been since
12896-520: The same thickness. The skull was fractured and the brain was visible. The upper torso was naked while the lower body was covered by a cloak made of a four-layered twill fabric and a fringed shawl. These two articles of clothing are now on display at the National Museum of Denmark in Copenhagen. It is uncertain if the body had been clothed at the time it had been deposited because the clothing from plant materials such as flax fibers can be passed in
13020-412: The sample since its burial. Alkali and acid washes can be used to remove humic acid and carbonate contamination, but care has to be taken to avoid removing the part of the sample that contains the carbon to be tested. Particularly for older samples, it may be useful to enrich the amount of C in the sample before testing. This can be done with a thermal diffusion column. The process takes about
13144-422: The satellites orbiting the Earth are present. The mesosphere is the third highest layer of Earth's atmosphere, occupying the region above the stratosphere and below the thermosphere. It extends from the stratopause at an altitude of about 50 km (31 mi; 160,000 ft) to the mesopause at 80–85 km (50–53 mi; 260,000–280,000 ft) above sea level. Temperatures drop with increasing altitude to
13268-401: The scalp had not occurred before death. The scientists were unable to make any conclusion as to the cause of death whether by murder, suicide, accident or natural causes. 56°47′40″N 9°34′32″E / 56.79444°N 9.57556°E / 56.79444; 9.57556 Radiocarbon dating Radiocarbon dating (also referred to as carbon dating or carbon-14 dating ) is
13392-447: The stratosphere lacks the weather-producing air turbulence that is so prevalent in the troposphere. Consequently, the stratosphere is almost completely free of clouds and other forms of weather. However, polar stratospheric or nacreous clouds are occasionally seen in the lower part of this layer of the atmosphere where the air is coldest. The stratosphere is the highest layer that can be accessed by jet-powered aircraft . The troposphere
13516-401: The surface water as carbonate and bicarbonate ions; at the same time the carbonate ions in the water are returning to the air as CO 2 . This exchange process brings C from the atmosphere into the surface waters of the ocean, but the C thus introduced takes a long time to percolate through the entire volume of the ocean. The deepest parts of the ocean mix very slowly with
13640-590: The surface waters, and as a result water from some deep ocean areas has an apparent radiocarbon age of several thousand years. Upwelling mixes this "old" water with the surface water, giving the surface water an apparent age of about several hundred years (after correcting for fractionation). This effect is not uniform – the average effect is about 400 years, but there are local deviations of several hundred years for areas that are geographically close to each other. These deviations can be accounted for in calibration, and users of software such as CALIB can provide as an input
13764-422: The surface waters, and the mixing is uneven. The main mechanism that brings deep water to the surface is upwelling, which is more common in regions closer to the equator. Upwelling is also influenced by factors such as the topography of the local ocean bottom and coastlines, the climate, and wind patterns. Overall, the mixing of deep and surface waters takes far longer than the mixing of atmospheric CO 2 with
13888-444: The temperature stabilizes over a large vertical distance through the rest of the troposphere. In the stratosphere , starting above about 20 km, the temperature increases with height, due to heating within the ozone layer caused by the capture of significant ultraviolet radiation from the Sun by the dioxygen and ozone gas in this region. Still another region of increasing temperature with altitude occurs at very high altitudes, in
14012-442: The thermopause varies considerably due to changes in solar activity. Because the thermopause lies at the lower boundary of the exosphere, it is also referred to as the exobase . The lower part of the thermosphere, from 80 to 550 kilometres (50 to 342 mi) above Earth's surface, contains the ionosphere . The temperature of the thermosphere gradually increases with height and can rise as high as 1500 °C (2700 °F), though
14136-429: The thermosphere. The exosphere contains many of the artificial satellites that orbit Earth. The thermosphere is the second-highest layer of Earth's atmosphere. It extends from the mesopause (which separates it from the mesosphere) at an altitude of about 80 km (50 mi; 260,000 ft) up to the thermopause at an altitude range of 500–1000 km (310–620 mi; 1,600,000–3,300,000 ft). The height of
14260-419: The total mass of the atmosphere is located in the lower 5.6 km (3.5 mi; 18,000 ft) of the troposphere. Nearly all atmospheric water vapor or moisture is found in the troposphere, so it is the layer where most of Earth's weather takes place. It has basically all the weather-associated cloud genus types generated by active wind circulation, although very tall cumulonimbus thunder clouds can penetrate
14384-478: The tree-ring data series has been extended to 13,900 years.) In the 1960s, Hans Suess was able to use the tree-ring sequence to show that the dates derived from radiocarbon were consistent with the dates assigned by Egyptologists. This was possible because although annual plants, such as corn, have a C / C ratio that reflects the atmospheric ratio at the time they were growing, trees only add material to their outermost tree ring in any given year, while
14508-430: The tropopause from below and rise into the lower part of the stratosphere. Most conventional aviation activity takes place in the troposphere, and it is the only layer accessible by propeller-driven aircraft . Within the five principal layers above, which are largely determined by temperature, several secondary layers may be distinguished by other properties: The average temperature of the atmosphere at Earth's surface
14632-404: The two. The atmospheric C / C ratio is lower in the southern hemisphere, with an apparent additional age of about 40 years for radiocarbon results from the south as compared to the north. This is because the greater surface area of ocean in the southern hemisphere means that there is more carbon exchanged between the ocean and the atmosphere than in the north. Since the surface ocean
14756-434: The value of N (the number of atoms of C remaining in the sample), the carbon-dating equation allows the calculation of N 0 – the number of atoms of C in the sample at the time the tree ring was formed – and hence the C / C ratio in the atmosphere at that time. Equipped with the results of carbon-dating the tree rings, it became possible to construct calibration curves designed to correct
14880-497: The ‰ sign indicates parts per thousand . Because the PDB standard contains an unusually high proportion of C , most measured δ C values are negative. For marine organisms, the details of the photosynthesis reactions are less well understood, and the δ C values for marine photosynthetic organisms are dependent on temperature. At higher temperatures, CO 2 has poor solubility in water, which means there
15004-411: Was awarded the Nobel Prize in Chemistry for this work. In nature, carbon exists as three isotopes . Carbon-12 ( C ) and carbon-13 ( C ) are stable and nonradioactive; carbon-14 ( C ), also known as "radiocarbon", is radioactive. The half-life of C (the time it takes for half of a given amount of C to decay ) is about 5,730 years, so its concentration in
15128-465: Was discovered in the Borremose bog about one kilometre away from the Borremose Man. The corpse is believed to be female, although decomposition made it difficult to be sure. The bog body was lying face down 60 cm (24 in) deep on a base of birch bark. In the immediate vicinity were birch branches; directly on the body were three approximately 10-centimetre-long (3.9 in) birch poles of
15252-465: Was recovered in 1948, approximately 400 metres (1,300 ft) south from Borremose man. Her approximate age range at the time of death was 20–35 years old. Borremose Woman was found lying face down, the body wrapped in a woollen garment. The scalp and hair on one side of the head had been separated; however, this was believed to be damage caused by the shovels of the peat diggers, not a cause of her death. The skull and face were crushed, and deterioration of
15376-785: Was then at Berkeley, learned of Korff's research and conceived the idea that it might be possible to use radiocarbon for dating. In 1945, Libby moved to the University of Chicago , where he began his work on radiocarbon dating. He published a paper in 1946 in which he proposed that the carbon in living matter might include C as well as non-radioactive carbon. Libby and several collaborators proceeded to experiment with methane collected from sewage works in Baltimore, and after isotopically enriching their samples they were able to demonstrate that they contained C . By contrast, methane created from petroleum showed no radiocarbon activity because of its age. The results were summarized in
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