Portal field news

Portal field news

in

🌏 | Humanity arrived in North America more than 2 years ago and found a footprint that overturned the conventional theory = US research team


写真 

Mankind arrived in North America more than 2 years ago and discovered a footprint that overturned the conventional theory = US research team

 
If you write the contents roughly
This means that old carbon can affect the results of radiocarbon dating in an aquatic environment, making the site look older than it really is.
 

A research team in New Mexico has recently been in the interior of the North American continent, 2 to 3000 years ago ... → Continue reading

 BBC NEWS JAPAN

From the news, readings, and feature articles of BBC journalists who interview in about 100 countries around the world, we select and deliver topics that are meaningful to Japanese users who are knowledgeable.


Wikipedia related words

If there is no explanation, there is no corresponding item on Wikipedia.

Radiocarbon dating

Radiocarbon dating(I'm sorry, I'm sorry,English: radiocarbon dating) Is naturalBiosphereWithinRadioisotopeIsCarbon-14 (14Based on the fact that the abundance ratio of C) is constant at the level of 1 per trillion.DatingIs the way[1]..The target is limited to the remains of animals and plants, and cannot be measured with inorganic substances and metals.

C14 datingIn addition to (Sea Fourteen)Carbon dating,Carbon-14 method,C14 methodAlso say.

Overview

In general, the abundance ratio of carbon-14 is almost constant in the living area of ​​the earth's nature.The abundance ratio inside animals and plants does not change until death, but after death, the supply of new carbon stops and the abundance ratio begins to decline.[1]..Dating is done by taking advantage of this property and the half-life of carbon-14 of 5730 years.[1]..Strictly speaking, the amount of carbon-14 produced is affected by fluctuations in the earth's magnetic field and solar activity, so the concentration in the atmosphere changes from year to year.In addition, the concentrations in the atmosphere are different between the northern hemisphere and the southern hemisphere.Radiocarbon dating is indicated by BP (Before Present or Before Physics), which is in the atmosphere.Nuclear testbyradiationNot much influenced by1950 Starting from, the actual age is indicated as how many years ago.

Origin of carbon-14

High-energy primary in the upper atmosphereCosmic rayIncluded in the secondary cosmic rays generated byneutronとnitrogenAtomic nucleus7.5 kg per year from the collision[2]Degree is generated.It is also released into the atmosphere through nuclear tests and reprocessing of nuclear fuel.[3]..The carbon-14 produced immediately combines with oxygen to form carbon dioxide, which diffuses into the atmosphere.However, although the annual fluctuation of the amount of production is estimated to be about 30%, it will be reduced to about 0.6% by exchanging with the ocean.[4].

Carbon-14 reduction

Carbon-14 (14C) is about 5730Half-lifeでBeta decaySince it has the property of decreasing, it is possible to estimate the age from the carbon isotope 12/14 ratio in the sample.If the measurement limit is about 1/1000 of the original, about 6 years ago will be the theoretical limit of the carbon-14 method (in actual measurement,Beta rayIn the case of the measurement method, the measurement limit is about 3-4 years, and in the AMS method, the measurement limit is about 4-5 years).

Moving to living things

Carbon-14 in carbon dioxide is taken up by plants by photosynthesis and spreads to animals in the food chain.Of living things細胞Carbon-14, which has settled inphotosynthesisIt is considered to decrease from the time when it was made in.That is, it is captured by photosynthesis.carbon dioxideReflects the amount of carbon-14 in the atmosphere, but no new carbon-14 is added after the inactivity of the organism.Therefore, when a sample is obtained from the remains of an organism and measured, it is possible to know when the carbon used in the cell was photosynthesized.For trees, insideAnnual ringsIs old and the outer annual rings are newly measured.

History

Measuring method

The first measurement method developed was to measure beta rays emitted when carbon-14 decays.Later, a method was developed to directly count carbon-14 in a sample.

Beta ray measurement method

It is called "gas proportional counting method" and "liquid scintillation counting method", and carbon-14 is used.ElectronicとAnti-electron neutrinoRelease nitrogen-14 (14N Beta rays emitted when decaying to the stable isotope nitrogen)ScintillatorIt is a method of detecting and counting by.Even 1 g of modern carbon breaks only once every 4-5 seconds, so measurement is time consuming and samples are required in grams.

In the gas proportional counting method, carbon-14 is converted into carbon dioxide gas and beta rays are measured.

Accelerator mass spectrometry (AMS) method

An analytical method developed in the late 1970s.acceleratorHow to count carbon-14 directly with AMS(Accelerator Mass Spectrometer) has significantly improved the required sample amount (about 1 mg) and measurement time (about 30 minutes-1 hour), and is more accurate and more efficient than the beta ray measurement method. It was made.In addition, it became possible to measure until about 6 years ago.With the miniaturization of the equipment, it has become available at many facilities.

Age error

Willard Libby, who discovered this measurement principle, reduced the half-life of carbon-14 to 5568 years.[Note 1]It is calculated as.In addition, when a plant fixes carbon, a phenomenon called isotope selection occurs, and the carbon-14 concentration and age of the sample differ depending on the plant species, so correction is necessary.The difference in carbon-14 concentration due to isotope selection can be achieved by accurately measuring the carbon-13 concentration, and the maximum correction amount is about 400 years.In other words, accurate identification of the age of paleontology also requires accurate understanding of modern isotope selections of the same species.

Age calibration

The amount of carbon-14 in the atmosphere has fluctuated, reflecting changes in cosmic rays and carbon release incidents accumulated in the ocean.Therefore, an error occurs in the measurement result.See belowVarve depositsandDendrochronologyThe age is calibrated by.In the dendrochronology, a correspondence table of radiocarbon dating (BP) up to about 12600 and the actual age is made.[5]..The old age, which is less than the annual ring age, was until about 24,000 years ago.CoralU / Th (uranium / thorium) It is collated with the age.

The age value calibrated using the calibration curve, that is, the carbon-14 age was calibrated (corrected against the standard) to the actual age, and the number of years starting from 1950 AD is calibrated. It is represented by "calBP" with "cal" meaning.Alternatively, when based on the Christian era, it is expressed as "calBC" or "calAD".The calibration age, also known as the calendar year, means "actual age."By the way, in the 14's of carbon,14It becomes "C BP".

In recent years, the probability method (High) is to obtain a more detailed probability distribution between the 13% probability and the 95.4% probability by performing mathematical statistical processing on the BP age value after isotope fractionation by δ68.2C. -A technique called Probability density range) is also used.

Marine reservoir effect

The carbon-14 concentration distribution in the atmosphere and hydrosphere is heterogeneous due to the effects of diffusion, circulation, and equilibrium.The surface seawater in the mid-latitude region is more than 400 years older than the atmosphere, and the deep seawater is more than 700 to 1000 years old.Furthermore, the age difference fluctuates depending on the times and regions.In addition, the atmosphere in the Southern Hemisphere is 40 years older than that in the Northern Hemisphere.In other words, in the case of organic matter originating from the atmosphere of the Southern Hemisphere, it is necessary to uniformly deduct 40 years.

Even in Japan, it has been found that the start time of the Yayoi period and the Kofun period is estimated to be older than the actual age by radiocarbon dating.This was clarified by making a calibration line by comparing with the dating of domestic annual rings and excavated materials.Especially for earthenware, it should be noted that since salt, which is a marine product, is indispensable for food storage and cooking, it is estimated to be up to several hundred years old due to the reservoir effect of marine products attached to the earthenware.[6].

Varve deposits

Of the striped patterns of material deposited on the calm bottom (freshwater and seawater), those deposited with a constant stratification year by yearVarveSedimentIt is called and can determine the exact age.The main collection sites are as follows.

Specific fluctuation

As mentioned above, the amount of carbon-14 produced varies depending on the amount of high-energy primary cosmic rays incident.Therefore, if the amount of cosmic rays incident increases for some reason, a large amount of carbon-14 will also be generated.[7]..If the amount of cosmic rays incident on the earth has increased in the past, the measurement results will be older than the actual age because the specimens that survived before the increase originally contained less carbon-14.Traces of such fluctuations were logged in 1956YakusugiIt has been discovered from the analysis of.According to the research group of Nagoya University, which discovered it, there was a rapid increase from 774 to 775 AD, which is more than 20 times the fluctuation associated with normal solar activity, and is the largest increase in the past 3000 years. Was showing[8]..In addition, a sharp increase is recorded in 994 AD.[7].

Systematic error

Contamination(pollution)
  • When collecting and storing samples, products of other ages may be mixed.[9]In addition, changes over time due to organisms during sample storage have been pointed out.[10].
  1. Natural factors: seawater origin around the sample (excavation), limestone, soil-derived organic acids, roots of other plants.
  2. Anthropogenic factors: Labeling directly on samples with marine products, carbon-containing markers, etc., pesticides, tobacco ash, packing with paper.
  • The content of decontamination work affects the measurement accuracy.
The sample itself is contaminated
  • Especially, it is said that carbon dating contains old carbon.Fossil fuel[Note 2]Plants that have absorbed the exhaust gas of automobiles using the car may indicate an era that is not possible in the first place.[Source required]The situation cannot be judged mechanically, and the possibility of arbitrariness and bias of the parties concerned cannot be ruled out.[Source required]

実 例

An example of an early measurement of a Japanese sample1950 -1955 Was investigated byNatsushima shell mound OfJomon PeriodWith oyster shells excavated from the early layerscharcoalThere is. In March and June 1959,University of MichiganからSosuke SugiharaIt was reported that the age values ​​by the carbon-14 dating method were shell BP9450 ± 400 and charcoal BP9240 ± 500.As a result, the early Jomon period was measured for the first time as 9500 years ago.Jomon potteryIt was pointed out that is the oldest pottery culture in the world.This surprised many Japanese archaeologists.Also requested measurementChosuke SerizawaAnd others claim that it was 3000 years ago from the age of the relics excavated on the continent.Sugao YamanouchiThere is a dispute with.

Higashitsugaru-gun, Aomori PrefectureSotogahama Town OfOhira Yamamoto I RuinsIt was announced in April 4500 that the pottery production period of the early Jomon period was 1 years ago (earlier), which is 6500 years older than the conventional wisdom.This real age isUniversity of WashingtonNora uses the international calibration curve (INTCAL 14), which converts the carbon-98 dating into calendar years using dendrochronological and coral dating.again,Yayoi PeriodThe beginning of the period was, according to popular wisdom, around the 5th century BC--around the 4th century BC, but in March 2003.National Museum of History and FolkloreAccording to the announcement, about 500 years old (early) about 3000 years ago (around the end of the 10th century BC, that is, the early Yayoi period in northern Kyushu is from 949 BC-915 BC, the early period is from about 810 BC, and the middle period is about 350 BC. The results go back to each of them.)

After that, it was found that the domestic calibration curve was different from the international calibration curve, and it was also found that the age was estimated to be older than the actual age due to the reservoir effect due to the salt content derived from seawater adhering to earthenware, etc., so the Jomon period began. There is still debate about when.

Source

Comparing these climatic events, which appear to be cold, with each of the Nordic Dryas seasons, they appear to be 2,000 to 3,000 years earlier.

footnote

[How to use footnotes]

注 釈

  1. ^ The true value is 5730.
  2. ^ Oil, coal, gas, etc.

Source

  1. ^ a b c Allison 2011 p.71
  2. ^ Allison 2011 pp.70-71
  3. ^ Carbon-14 Nuclear Materials Information Room
  4. ^ ICRR News No.41 2000.8.1 University of Tokyo Institute for Cosmic Ray Research (PDF)
  5. ^ a b Varve of Lake Suigetsu: Standard clock for the past 7 years (PDF) Japan Geoscience Union Newsletter. November, 2010. Vol.6. No.4. November 2010, 11
  6. ^ Livelihood from the viewpoint of pottery usage during the Yayoi migration period National Museum of Japanese History and Folklore Research Report Vol. 185 February 2014
  7. ^ a b Fusa Miyake, Kimiaki Masuda, etc.Sudden cosmic ray event engraved on tree rings Nagoya University Accelerator Mass Spectrometer Performance Report. V.25, 2014, p.137-143
  8. ^ Traces of increased cosmic rays in 774-775 AD during the annual rings of Japanese trees Nagoya University (PDF)
  9. ^ Sample contamination and removal of contamination by pretreatment Beta Analytical Radiocarbon Dating Laboratory
  10. ^ Hiroshi Takahashi, Sorako Handa, Masayo Minami, etc.Storage of groundwater samples and changes in carbon isotope ratio over time Japan Geoscience Union 2015 AHW24-P07 (PDF)

References

Related item

外部 リンク


 

Back to Top
Close