{"id":1905,"date":"2026-09-16T15:10:55","date_gmt":"2026-09-16T15:10:55","guid":{"rendered":"https:\/\/physicsfundamentalsinfo.com\/blog\/?p=1905"},"modified":"2026-09-16T15:10:57","modified_gmt":"2026-09-16T15:10:57","slug":"carbon-dating","status":"publish","type":"post","link":"https:\/\/physicsfundamentalsinfo.com\/blog\/nuclear-physics\/carbon-dating\/","title":{"rendered":"Carbon Dating: The Physics Behind It"},"content":{"rendered":"\n<div class=\"pf-citation\"><div class=\"eyebrow\">Definition<\/div><p>\nCarbon dating is a method for working out when a once-living thing died, by measuring how much carbon-14 it still holds. A living organism keeps its carbon-14 topped up from the atmosphere. That exchange stops at death, and the isotope decays with a half-life near 5,700 years, so the surviving fraction fixes the age.\n<\/p><\/div>\n\n<p>A lump of charcoal from an old fire looks like any other lump of charcoal. Nothing about it announces its age. Yet a laboratory can take a few milligrams, count what is inside, and say roughly how long ago the tree that made it stopped growing.<\/p>\n\n<p>The trick is that every living thing carries a faint radioactive label it cannot switch off. While the organism is alive, that label is topped up continuously. The moment it dies the topping-up stops, and the label starts to fade on a schedule that has not changed in tens of thousands of years.<\/p>\n\n<h2>What Is Carbon Dating?<\/h2>\n\n<p>Carbon dating is the measurement of the carbon-14 left in once-living material, read against the level that material started with, to estimate how long ago it died.<\/p>\n\n<p>Notice what that sentence does not say. It does not say the method measures age. A laboratory measures a carbon-14 level; the age is what the decay law infers from that level, and the inference rests on assumptions you can state out loud and check.<\/p>\n\n<p>In a research paper the method is called radiocarbon dating, and the two names mean the same thing. &#8220;Carbon dating&#8221; is the everyday name; &#8220;radiocarbon&#8221; is what appears on the report a laboratory sends back.<\/p>\n\n<p>Three conditions have to hold before the method has anything at all to say.<\/p>\n\n<ul>\n<li><strong>The carbon must have been in circulation with the atmosphere.<\/strong> Wood, charcoal, bone, seeds, textiles, leather, shell and peat all qualify, because a living thing builds itself out of the carbon moving around it. Granite does not, and neither does a bronze blade or a clay pot, though charcoal trapped in the clay might.<\/li>\n<li><strong>That exchange must have stopped.<\/strong> For an organism, death is what stops it, and the stopping is the event the clock is timing \u2014 not the age of the object, but the moment the carbon stopped being refreshed.<\/li>\n<li><strong>The starting level must be known.<\/strong> The arithmetic compares what is left with what was there at the start, and getting that starting level right is the hardest part of the whole business.<\/li>\n<\/ul>\n\n<h2>The Carbon Dating Formula and How to Read It<\/h2>\n\n<p>Every radioactive isotope thins out by the same law, and carbon-14 is no exception. Turn that law around, solve for time rather than for the amount left, and you get the equation a dating laboratory actually uses.<\/p>\n\n<div class=\"pf-formula\">t = (t\u00bd \/ ln 2) \u00b7 ln(N<sub>0<\/sub> \/ N)<\/div>\n\n<div class=\"pf-table-scroll\" style=\"display:block;width:100%;max-width:100%;overflow-x:auto;-webkit-overflow-scrolling:touch;margin:1.5em 0;\">\n<table style=\"width:100%;border-collapse:collapse;word-break:break-word;\">\n<thead>\n<tr>\n<th style=\"text-align:left;padding:8px;border-bottom:2px solid #D9CFB8;\">Symbol<\/th>\n<th style=\"text-align:left;padding:8px;border-bottom:2px solid #D9CFB8;\">Quantity<\/th>\n<th style=\"text-align:left;padding:8px;border-bottom:2px solid #D9CFB8;\">Unit<\/th>\n<th style=\"text-align:left;padding:8px;border-bottom:2px solid #D9CFB8;\">Notes<\/th>\n<\/tr>\n<\/thead>\n<tbody>\n<tr><td style=\"padding:8px;border-bottom:1px solid #D9CFB8;\">t<\/td><td style=\"padding:8px;border-bottom:1px solid #D9CFB8;\">elapsed time since death<\/td><td style=\"padding:8px;border-bottom:1px solid #D9CFB8;\">years<\/td><td style=\"padding:8px;border-bottom:1px solid #D9CFB8;\">reported as radiocarbon years before 1950, not as a calendar date<\/td><\/tr>\n<tr><td style=\"padding:8px;border-bottom:1px solid #D9CFB8;\">t\u00bd<\/td><td style=\"padding:8px;border-bottom:1px solid #D9CFB8;\">half-life of carbon-14<\/td><td style=\"padding:8px;border-bottom:1px solid #D9CFB8;\">years<\/td><td style=\"padding:8px;border-bottom:1px solid #D9CFB8;\">three values are in circulation: 5,568, 5,700 and 5,730 years. Say which one you used<\/td><\/tr>\n<tr><td style=\"padding:8px;border-bottom:1px solid #D9CFB8;\">N<sub>0<\/sub><\/td><td style=\"padding:8px;border-bottom:1px solid #D9CFB8;\">carbon-14 level at death<\/td><td style=\"padding:8px;border-bottom:1px solid #D9CFB8;\">percent of the modern standard<\/td><td style=\"padding:8px;border-bottom:1px solid #D9CFB8;\">the atmospheric level when the organism died; usually assumed to be 100<\/td><\/tr>\n<tr><td style=\"padding:8px;border-bottom:1px solid #D9CFB8;\">N<\/td><td style=\"padding:8px;border-bottom:1px solid #D9CFB8;\">carbon-14 level measured today<\/td><td style=\"padding:8px;border-bottom:1px solid #D9CFB8;\">percent of the modern standard<\/td><td style=\"padding:8px;border-bottom:1px solid #D9CFB8;\">what the instrument reports, written pMC<\/td><\/tr>\n<tr><td style=\"padding:8px;border-bottom:1px solid #D9CFB8;\">\u03bb<\/td><td style=\"padding:8px;border-bottom:1px solid #D9CFB8;\">decay constant<\/td><td style=\"padding:8px;border-bottom:1px solid #D9CFB8;\">per year<\/td><td style=\"padding:8px;border-bottom:1px solid #D9CFB8;\">\u03bb = ln 2 \/ t\u00bd, which is 0.00012160 per year at 5,700 years<\/td><\/tr>\n<tr><td style=\"padding:8px;border-bottom:1px solid #D9CFB8;\">\u03c4<\/td><td style=\"padding:8px;border-bottom:1px solid #D9CFB8;\">mean lifetime<\/td><td style=\"padding:8px;border-bottom:1px solid #D9CFB8;\">years<\/td><td style=\"padding:8px;border-bottom:1px solid #D9CFB8;\">\u03c4 = t\u00bd \/ ln 2 = 8,223.3617 years at 5,700 years; the constant that turns a percentage into years<\/td><\/tr>\n<\/tbody>\n<\/table>\n<\/div>\n\n<p>Run the same law forwards and it describes the fading itself, which is the form you meet first in a textbook:<\/p>\n\n<div class=\"pf-formula\">N = N<sub>0<\/sub> \u00b7 e<sup>-\u03bbt<\/sup>, with \u03bb = ln 2 \/ t\u00bd<\/div>\n\n<p>The <a href=\"https:\/\/physicsfundamentalsinfo.com\/blog\/nuclear-physics\/half-life-physics\/\">half-life<\/a> is the only property of the isotope in either equation. Everything else is bookkeeping: divide the measured level by the starting level, take a logarithm, multiply by a constant.<\/p>\n\n<p>You do not have to work that logarithm by hand. Our <a href=\"https:\/\/physicsfundamentalsinfo.com\/calculators\/half-life\">half-life calculator<\/a> solves exactly this equation \u2014 set N<sub>0<\/sub> = 100, set N to the measured percentage of modern carbon, type in the half-life you have chosen, and solve for elapsed time. Its own default is the 5,730-year value, so change that field if you want the 5,700-year figure used throughout this article: the 5,730-year and 5,568-year settings differ by 2.9095 %, the ratio 5730\/5568, on every reading you put in.<\/p>\n\n<p>The lab below lets you drive the same arithmetic by hand. You set what the instrument measured, what the atmosphere held when the organism died, and how precise the measurement was; the readouts report the radiocarbon age, its range, and what the same reading would give under the other two half-lives.<\/p>\n\n<p>Two things are worth watching for. The uncertainty slider never moves the age itself, only the width of the bar around it \u2014 and switching half-life changes the age while leaving the measured fraction exactly where it was.<\/p>\n\n<div class=\"pf-sim-slot\"><div class=\"pf-sim-slot-header\"><span class=\"icon-dot\"><\/span><span class=\"label\">Carbon Dating Lab<\/span><\/div><div class=\"pf-sim-slot-body\"><style>.pf-sim-frame{width:100%;border:none;height:600px}@media(max-width:760px){.pf-sim-frame{height:1040px}}<\/style><iframe src=\"\/labs\/carbon-dating.html?embed=1\" class=\"pf-sim-frame\" loading=\"lazy\"><\/iframe><\/div><\/div>\n\n<h2>Where the Carbon-14 Comes From, and Why It Stops<\/h2>\n\n<p>Where does the carbon-14 come from in the first place, and what exactly stops? Carbon-14 is manufactured high in the atmosphere. Cosmic rays produce neutrons there, and a neutron that has slowed down can strike a nitrogen-14 nucleus and knock a proton out of it. The nucleus keeps its mass number of 14 but loses a unit of charge, so it is now carbon rather than nitrogen.<\/p>\n\n<p>That fresh carbon-14 oxidises, joins the vast reservoir of carbon dioxide in the air and mixes around the globe. Plants take it up when they photosynthesise. Animals take it up when they eat plants, or eat animals that ate plants. Every living thing therefore sits at roughly the same carbon-14 level as the air around it.<\/p>\n\n<p>Carbon-14 is unstable, and it goes by <a href=\"https:\/\/physicsfundamentalsinfo.com\/blog\/nuclear-physics\/beta-decay\/\">beta-minus decay<\/a>: a neutron inside the nucleus turns into a proton, emitting an electron and an <a href=\"https:\/\/physicsfundamentalsinfo.com\/blog\/modern-physics\/neutrino-ghost-particle\/\">antineutrino<\/a>. The nucleus becomes nitrogen-14 again, which is where the carbon came from in the first place.<\/p>\n\n<p>The decay leaves the daughter nucleus in its ground state, so no <a href=\"https:\/\/physicsfundamentalsinfo.com\/blog\/nuclear-physics\/gamma-rays-properties-uses\/\">gamma rays<\/a> come out of it. All a detector has to work with is one low-energy electron, and that constraint has shaped how carbon-14 has been measured ever since.<\/p>\n\n<p>While the organism lives, decay and replacement balance each other and the level holds steady. Death breaks the balance. Nothing new comes in, decay carries on regardless, and from that moment the carbon-14 level falls along a curve that depends only on how long the organism has been dead.<\/p>\n\n<figure style=\"margin:32px auto;max-width:720px;text-align:center;\">\n  <img src=\"https:\/\/physicsfundamentalsinfo.com\/blog\/wp-content\/uploads\/2026\/09\/carbon-dating-diagram-01-768x564.jpg\" srcset=\"https:\/\/physicsfundamentalsinfo.com\/blog\/wp-content\/uploads\/2026\/09\/carbon-dating-diagram-01-768x564.jpg 768w, https:\/\/physicsfundamentalsinfo.com\/blog\/wp-content\/uploads\/2026\/09\/carbon-dating-diagram-01.jpg 1240w\" sizes=\"auto, (max-width: 760px) 100vw, 720px\" width=\"1240\" height=\"910\" alt=\"Two panels comparing the same organism alive and dead. In the left panel, cosmic rays make carbon-14 in the atmosphere and two gold arrows run both ways between the atmosphere box and a living plant or animal, labelled takes carbon in and gives carbon back, so the level holds steady and no clock is running yet. In the right panel the same two arrows are greyed and dashed and a wine-coloured cross is drawn over them, labelled death cuts the exchange; the organism box reads dead tissue, sealed off, carbon-14 only decays away, and the clock starts here. A dark band along the bottom reads: carbon dating measures the carbon-14 that is left, and dates the moment the exchange stopped.\" loading=\"lazy\" decoding=\"async\" style=\"width:100%;height:auto;border-radius:4px;\">\n  <figcaption style=\"font-size:13px;color:#1F2E47;font-style:italic;margin-top:8px;\">Figure 1. The exchange that makes carbon dating possible, and the event that ends it. While the organism is alive its carbon-14 is renewed from the air as fast as it decays. Death cuts the link, and only then does the clock start.<\/figcaption>\n<\/figure>\n\n<h2>Reading an Age From a Measurement<\/h2>\n\n<p>Laboratories do not report a raw count. They report percent modern carbon, written pMC: the sample&#8217;s carbon-14 level as a percentage of an agreed 1950 standard. Because it is a ratio, no activity constant and no absolute count ever needs to appear in the arithmetic.<\/p>\n\n<p>A reading of 50.0 pMC means half the original carbon-14 has gone, which is one half-life. A reading of 25.0 pMC is two half-lives, 12.5 pMC is three, and so on down. Between those landmarks the logarithm does the work.<\/p>\n\n<p>Plot the level on a logarithmic axis and something useful happens: the curve straightens out. Equal steps down the axis are equal steps in time, so the half-life ladder becomes a set of evenly spaced rungs rather than a curve that flattens out and becomes hard to read.<\/p>\n\n<figure style=\"margin:32px auto;max-width:720px;text-align:center;\">\n  <img src=\"https:\/\/physicsfundamentalsinfo.com\/blog\/wp-content\/uploads\/2026\/09\/carbon-dating-diagram-02-768x577.jpg\" srcset=\"https:\/\/physicsfundamentalsinfo.com\/blog\/wp-content\/uploads\/2026\/09\/carbon-dating-diagram-02-768x577.jpg 768w, https:\/\/physicsfundamentalsinfo.com\/blog\/wp-content\/uploads\/2026\/09\/carbon-dating-diagram-02.jpg 1240w\" sizes=\"auto, (max-width: 760px) 100vw, 720px\" width=\"1240\" height=\"932\" alt=\"Graph of the percentage of modern carbon left in a sample against radiocarbon years before 1950. The horizontal axis runs from 0 to 60,000 years with ticks every 10,000 years; the vertical axis is logarithmic and runs from 0.1 to 100 percent with gridlines at 0.1, 1, 10 and 100. Because the axis is logarithmic the decay is a single straight gold line falling from 100 percent at zero years to 0.1 percent near 56,800 years. Four ringed points mark the half-life ladder: 50 percent left at 5,700 years, 25 percent at 11,400, 12.5 percent at 17,100 and 6.25 percent at 22,800, each joined to both axes by dotted guide lines. A fifth ringed point marks 0.3 percent at 47,770 years. A mist-coloured band covers everything beyond 50,000 years and is labelled beyond the method.\" loading=\"lazy\" decoding=\"async\" style=\"width:100%;height:auto;border-radius:4px;\">\n  <figcaption style=\"font-size:13px;color:#1F2E47;font-style:italic;margin-top:8px;\">Figure 2. Carbon-14 remaining against radiocarbon age, on a logarithmic vertical axis and at a half-life of 5,700 years. The evenly spaced rungs at 50 %, 25 %, 12.5 % and 6.25 % are the successive half-lives. A mist band covers everything past 50,000 years, where the reading runs into laboratory background.<\/figcaption>\n<\/figure>\n\n<p>The table reads that same line off at nine levels, all at a half-life of 5,700 years and all assuming the organism started at the 1950 standard. Column three tells you how many half-lives deep a reading is, which is the quickest way to place it; column four carries the age itself, and it is the one to quote.<\/p>\n\n<div class=\"pf-table-scroll\" style=\"display:block;width:100%;max-width:100%;overflow-x:auto;-webkit-overflow-scrolling:touch;margin:1.5em 0;\">\n<table style=\"width:100%;border-collapse:collapse;word-break:break-word;\">\n<thead>\n<tr>\n<th style=\"text-align:left;padding:8px;border-bottom:2px solid #D9CFB8;\">Measured level (pMC)<\/th>\n<th style=\"text-align:right;padding:8px;border-bottom:2px solid #D9CFB8;\">Fraction left<\/th>\n<th style=\"text-align:right;padding:8px;border-bottom:2px solid #D9CFB8;\">Half-lives elapsed<\/th>\n<th style=\"text-align:right;padding:8px;border-bottom:2px solid #D9CFB8;\">Radiocarbon age (years BP)<\/th>\n<\/tr>\n<\/thead>\n<tbody>\n<tr><td style=\"padding:8px;border-bottom:1px solid #D9CFB8;\">100<\/td><td style=\"text-align:right;padding:8px;border-bottom:1px solid #D9CFB8;\">1.00000<\/td><td style=\"text-align:right;padding:8px;border-bottom:1px solid #D9CFB8;\">0.0000<\/td><td style=\"text-align:right;padding:8px;border-bottom:1px solid #D9CFB8;\">0<\/td><\/tr>\n<tr><td style=\"padding:8px;border-bottom:1px solid #D9CFB8;\">90<\/td><td style=\"text-align:right;padding:8px;border-bottom:1px solid #D9CFB8;\">0.90000<\/td><td style=\"text-align:right;padding:8px;border-bottom:1px solid #D9CFB8;\">0.1520<\/td><td style=\"text-align:right;padding:8px;border-bottom:1px solid #D9CFB8;\">870<\/td><\/tr>\n<tr><td style=\"padding:8px;border-bottom:1px solid #D9CFB8;\">75<\/td><td style=\"text-align:right;padding:8px;border-bottom:1px solid #D9CFB8;\">0.75000<\/td><td style=\"text-align:right;padding:8px;border-bottom:1px solid #D9CFB8;\">0.4150<\/td><td style=\"text-align:right;padding:8px;border-bottom:1px solid #D9CFB8;\">2,370<\/td><\/tr>\n<tr><td style=\"padding:8px;border-bottom:1px solid #D9CFB8;\">50<\/td><td style=\"text-align:right;padding:8px;border-bottom:1px solid #D9CFB8;\">0.50000<\/td><td style=\"text-align:right;padding:8px;border-bottom:1px solid #D9CFB8;\">1.0000<\/td><td style=\"text-align:right;padding:8px;border-bottom:1px solid #D9CFB8;\">5,700<\/td><\/tr>\n<tr><td style=\"padding:8px;border-bottom:1px solid #D9CFB8;\">25<\/td><td style=\"text-align:right;padding:8px;border-bottom:1px solid #D9CFB8;\">0.25000<\/td><td style=\"text-align:right;padding:8px;border-bottom:1px solid #D9CFB8;\">2.0000<\/td><td style=\"text-align:right;padding:8px;border-bottom:1px solid #D9CFB8;\">11,400<\/td><\/tr>\n<tr><td style=\"padding:8px;border-bottom:1px solid #D9CFB8;\">12.5<\/td><td style=\"text-align:right;padding:8px;border-bottom:1px solid #D9CFB8;\">0.12500<\/td><td style=\"text-align:right;padding:8px;border-bottom:1px solid #D9CFB8;\">3.0000<\/td><td style=\"text-align:right;padding:8px;border-bottom:1px solid #D9CFB8;\">17,100<\/td><\/tr>\n<tr><td style=\"padding:8px;border-bottom:1px solid #D9CFB8;\">6.25<\/td><td style=\"text-align:right;padding:8px;border-bottom:1px solid #D9CFB8;\">0.06250<\/td><td style=\"text-align:right;padding:8px;border-bottom:1px solid #D9CFB8;\">4.0000<\/td><td style=\"text-align:right;padding:8px;border-bottom:1px solid #D9CFB8;\">22,800<\/td><\/tr>\n<tr><td style=\"padding:8px;border-bottom:1px solid #D9CFB8;\">1<\/td><td style=\"text-align:right;padding:8px;border-bottom:1px solid #D9CFB8;\">0.01000<\/td><td style=\"text-align:right;padding:8px;border-bottom:1px solid #D9CFB8;\">6.6439<\/td><td style=\"text-align:right;padding:8px;border-bottom:1px solid #D9CFB8;\">37,870<\/td><\/tr>\n<tr><td style=\"padding:8px;border-bottom:1px solid #D9CFB8;\">0.3<\/td><td style=\"text-align:right;padding:8px;border-bottom:1px solid #D9CFB8;\">0.00300<\/td><td style=\"text-align:right;padding:8px;border-bottom:1px solid #D9CFB8;\">8.3808<\/td><td style=\"text-align:right;padding:8px;border-bottom:1px solid #D9CFB8;\">47,770<\/td><\/tr>\n<\/tbody>\n<\/table>\n<\/div>\n\n<p>Every age in that last column is rounded to the nearest ten years, which is the convention for reported radiocarbon ages. Carry the unrounded figures through your own working and round once, at the end \u2014 rounding the number of half-lives first and then multiplying will shift the answer by a decade or more.<\/p>\n\n<p>How the level is measured has changed. Early work counted the <a href=\"https:\/\/physicsfundamentalsinfo.com\/blog\/nuclear-physics\/types-of-radiation-physics\/\">beta particles<\/a> coming out of a sample and needed grams of material and days of counting. Accelerator mass spectrometry counts carbon-14 atoms directly, which is why a few milligrams now suffice.<\/p>\n\n<p>The uncertainty behaves in a way most people find surprising. A measurement precise to \u00b1 0.5 % of the reading gives \u00b1 41 years at 5,700 years old, and the same \u00b1 41 years at 37,870 years old. The error bar in years depends only on the relative precision and the mean lifetime, not on the age.<\/p>\n\n<p>Why do old dates feel less precise, then? Because the relative precision itself gets worse. There is so little carbon-14 left in a very old sample that counting it well becomes genuinely hard, and it is that, not the arithmetic, that widens the bar.<\/p>\n\n<h2>Why Ages Are Given in Radiocarbon Years BP<\/h2>\n\n<p>A radiocarbon age is not a calendar age, and the difference is not a technicality. What the equation returns is a count of <em>radiocarbon years before present<\/em>, where &#8220;present&#8221; is fixed at 1950, and the count assumes the atmosphere always held the 1950 carbon-14 level.<\/p>\n\n<p>It did not. Atmospheric carbon-14 has wandered, and it has wandered in both directions within living memory.<\/p>\n\n<ul>\n<li><strong>Down, through the industrial period.<\/strong> Burning coal and oil releases carbon that is far too old to hold any carbon-14 at all, so the fossil carbon diluted the atmosphere. This is the Suess effect, and it makes wood grown in the early twentieth century read slightly older than it is.<\/li>\n<li><strong>Up, and sharply, after 1950.<\/strong> Above-ground nuclear weapons testing roughly doubled atmospheric carbon-14 by the early 1960s. The level has been falling back ever since, which is why anything grown in the second half of the twentieth century can read as a negative radiocarbon age.<\/li>\n<\/ul>\n\n<p>Because of that wandering, turning radiocarbon years into a calendar date needs a published calibration curve \u2014 a record built from material whose true age is known independently. This article does not carry one, and no page on this site converts a radiocarbon age into a calendar year.<\/p>\n\n<p>So read a figure like &#8220;11,400 radiocarbon years BP&#8221; for what it is: the answer the decay equation gives, on a stated half-life, before calibration. It is a real, reproducible number. It is just not a date.<\/p>\n\n<h2>The Three Half-Lives, and Why Reported Ages Still Use 5,568 Years<\/h2>\n\n<p>Ask what the half-life of carbon-14 is and you will be given one of three answers, all of them defensible. The currently recommended value is about 5,700 years. An older and still widely quoted measurement, the Cambridge value, is 5,730 years \u2014 the default on our own half-life calculator. The original Libby value is 5,568 years.<\/p>\n\n<p>Here is the part that surprises people: reported radiocarbon ages are still computed with the Libby figure, by convention, even though it is not the best measurement. That is deliberate. Keeping one agreed constant means an age published decades ago and an age published this year can be compared directly, and the calibration step absorbs the difference afterwards.<\/p>\n\n<figure style=\"margin:32px auto;max-width:720px;text-align:center;\">\n  <img src=\"https:\/\/physicsfundamentalsinfo.com\/blog\/wp-content\/uploads\/2026\/09\/carbon-dating-diagram-03-768x441.jpg\" srcset=\"https:\/\/physicsfundamentalsinfo.com\/blog\/wp-content\/uploads\/2026\/09\/carbon-dating-diagram-03-768x441.jpg 768w, https:\/\/physicsfundamentalsinfo.com\/blog\/wp-content\/uploads\/2026\/09\/carbon-dating-diagram-03.jpg 1240w\" sizes=\"auto, (max-width: 760px) 100vw, 720px\" width=\"1240\" height=\"712\" alt=\"Three horizontal bars drawn to the same scale, all from one measurement of 25.0 percent modern carbon. The scale runs from 0 to 12,000 radiocarbon years before 1950 with ticks every 3,000 years. The Libby 5,568-year half-life, labelled the convention for reported ages, gives 11,140 years, written on the bar as 11,140 reported and 11,136 unrounded; the current 5,700-year value, labelled the best modern value, gives 11,400 years; the Cambridge 5,730-year value, labelled our half-life calculator default, gives 11,460 years. Dotted lines from the shortest and the longest bar end mark the gap between the unrounded ages, labelled 324 years.\" loading=\"lazy\" decoding=\"async\" style=\"width:100%;height:auto;border-radius:4px;\">\n  <figcaption style=\"font-size:13px;color:#1F2E47;font-style:italic;margin-top:8px;\">Figure 3. One measurement of 25.0 pMC, read with each of the three half-lives. The bars are drawn to the same scale, and to the unrounded ages 11,136, 11,400 and 11,460 years; the gap between the shortest and the longest is 11,460 &#8211; 11,136 = 324 years, or 2.9095 % of the Libby age, and that same percentage applies at every reading.<\/figcaption>\n<\/figure>\n\n<div class=\"pf-table-scroll\" style=\"display:block;width:100%;max-width:100%;overflow-x:auto;-webkit-overflow-scrolling:touch;margin:1.5em 0;\">\n<table style=\"width:100%;border-collapse:collapse;word-break:break-word;\">\n<thead>\n<tr>\n<th style=\"text-align:left;padding:8px;border-bottom:2px solid #D9CFB8;\">Half-life<\/th>\n<th style=\"text-align:left;padding:8px;border-bottom:2px solid #D9CFB8;\">Name<\/th>\n<th style=\"text-align:left;padding:8px;border-bottom:2px solid #D9CFB8;\">What it is used for<\/th>\n<th style=\"text-align:right;padding:8px;border-bottom:2px solid #D9CFB8;\">Age from 25.0 pMC<\/th>\n<th style=\"text-align:right;padding:8px;border-bottom:2px solid #D9CFB8;\">Against the Libby age<\/th>\n<\/tr>\n<\/thead>\n<tbody>\n<tr><td style=\"padding:8px;border-bottom:1px solid #D9CFB8;\">5,568 years<\/td><td style=\"padding:8px;border-bottom:1px solid #D9CFB8;\">Libby<\/td><td style=\"padding:8px;border-bottom:1px solid #D9CFB8;\">the convention for reported radiocarbon ages, kept so that old and new dates stay comparable<\/td><td style=\"text-align:right;padding:8px;border-bottom:1px solid #D9CFB8;\">11,140 (11,136 unrounded)<\/td><td style=\"text-align:right;padding:8px;border-bottom:1px solid #D9CFB8;\">reference<\/td><\/tr>\n<tr><td style=\"padding:8px;border-bottom:1px solid #D9CFB8;\">5,700 years<\/td><td style=\"padding:8px;border-bottom:1px solid #D9CFB8;\">currently recommended<\/td><td style=\"padding:8px;border-bottom:1px solid #D9CFB8;\">the best modern value, and the default in the lab above and everywhere in this article<\/td><td style=\"text-align:right;padding:8px;border-bottom:1px solid #D9CFB8;\">11,400<\/td><td style=\"text-align:right;padding:8px;border-bottom:1px solid #D9CFB8;\">+ 2.3707 %<\/td><\/tr>\n<tr><td style=\"padding:8px;border-bottom:1px solid #D9CFB8;\">5,730 years<\/td><td style=\"padding:8px;border-bottom:1px solid #D9CFB8;\">Cambridge<\/td><td style=\"padding:8px;border-bottom:1px solid #D9CFB8;\">common in textbooks, and the default on our half-life calculator<\/td><td style=\"text-align:right;padding:8px;border-bottom:1px solid #D9CFB8;\">11,460<\/td><td style=\"text-align:right;padding:8px;border-bottom:1px solid #D9CFB8;\">+ 2.9095 %<\/td><\/tr>\n<\/tbody>\n<\/table>\n<\/div>\n\n<p>The last column is worked from the unrounded Libby age, because the reported ages have already been rounded to the nearest ten years: 11,400 \/ 11,136 = 1.023707, which is + 2.3707 %, and 11,460 \/ 11,136 = 1.0290948, which is + 2.9095 %. Take those ratios against the rounded 11,140 instead and you get 2.3339 % and 2.8725 %, which is why a percentage is only ever as good as the figure it was measured against.<\/p>\n\n<p>None of the three is wrong, and the choice is not a matter of taste either. It is a declaration: every quoted radiocarbon age is meaningless until you say which half-life produced it. Problem 3 works the difference through in full.<\/p>\n\n<h2>How Far Back Can Carbon Dating Go?<\/h2>\n\n<p>Carbon dating reaches back about 50,000 years, and that ceiling is set by what a laboratory can measure rather than by anything in the equation. The exponential itself never reaches zero.<\/p>\n\n<p>Follow the numbers down and you can see the wall coming. At 37,870 radiocarbon years a sample still holds 1 % of modern carbon. At 47,770 years it holds 0.3 %. By 51,100 years it is down to 0.2 %, and one slider step of 0.1 pMC between those two readings is worth more than three thousand years of age.<\/p>\n\n<p>Down there, two things start to dominate. Laboratory equipment has its own faint background signal, and any modern carbon picked up during handling adds carbon-14 of its own. Neither can be separated from a genuine signal that is itself only a few tenths of a percent, and Problem 6 works out what even a one-percent trace does to a reading that faint.<\/p>\n\n<p>So treat &#8220;about 50,000 years&#8221; as a working horizon rather than a sharp edge. Careful laboratories push a little past it on well-preserved material; ordinary samples fall short of it. There is no line in the physics where dating simply stops.<\/p>\n\n<h2>What Ruins a Date: Contamination and Reservoir Effects<\/h2>\n\n<p>Contamination is the great enemy of an old date, and it is brutally asymmetric. A trace of modern carbon in an ancient sample is a disaster; the same trace of ancient carbon in a young sample barely registers.<\/p>\n\n<p>Work an example. A sample genuinely at 1.0 pMC, an age of 37,870 radiocarbon years, picks up 1 % modern carbon during collection. Its measured level becomes 1.99 pMC and its apparent age falls to 32,210 years \u2014 younger by 5,660 years, from a one-percent error.<\/p>\n\n<p>Now do the same 1 % to a sample reading 50.0 pMC. It measures 50.5 pMC, and the age moves from 5,700 to 5,620 radiocarbon years: a shift of 80 years. Same contamination, same fraction, seventy times less damage.<\/p>\n\n<p>Reservoir effects are a different problem, and they are not laboratory errors at all. Carbon in the deep ocean has been out of contact with the atmosphere for a long time, so marine organisms \u2014 and the animals that eat them \u2014 start life already depleted in carbon-14 and can read older than they really are.<\/p>\n\n<p>The same thing happens in fresh water fed by old limestone, and near volcanic vents that breathe out carbon-free gas. The size of the offset varies with place and setting, and no single number covers it, so this article puts no figure on it.<\/p>\n\n<h2>Common Misconceptions About Carbon Dating<\/h2>\n\n<p>Four beliefs about this method are worth correcting, and the first is far and away the most common.<\/p>\n\n<ul>\n<li><strong>&#8220;Carbon dating can date dinosaur bones.&#8221;<\/strong> It cannot. At 66 million years a fossil is about 11,600 carbon-14 half-lives past death, and nothing whatever is left to measure. Dinosaur fossils are dated from the rocks around them, using isotope systems whose half-lives run to hundreds of millions or billions of years.<\/li>\n<li><strong>&#8220;Carbon dating works on rocks.&#8221;<\/strong> It does not. What the clock times is a parcel of carbon ceasing to exchange with the atmosphere: for an organism that moment is death, and for deep ocean water it is the moment the water left the surface. A granite boulder never exchanged carbon with the atmosphere in the first place, so for granite that moment never came and there is no clock in it to read.<\/li>\n<li><strong>&#8220;A radiocarbon date is a calendar date.&#8221;<\/strong> It is not, until it has been calibrated. An uncalibrated age is a count of radiocarbon years before 1950, computed on a stated half-life.<\/li>\n<li><strong>&#8220;The method measures how old something is.&#8221;<\/strong> It measures how much carbon-14 is left. The age is inferred from that measurement through a model, and the model can be wrong about the starting level even when the measurement is perfect.<\/li>\n<\/ul>\n\n<figure style=\"margin:32px auto;max-width:640px;text-align:center;\">\n  <img decoding=\"async\" src=\"https:\/\/physicsfundamentalsinfo.com\/blog\/wp-content\/uploads\/2026\/09\/a-dinosaur-fossil-on-museum-display.jpg\"\n       alt=\"Mounted dinosaur fossil skeleton in a museum, the kind of specimen carbon dating cannot date\"\n       loading=\"lazy\"\n       style=\"width:100%;height:auto;border-radius:4px;\" width=\"1920\" height=\"1440\">\n  <figcaption style=\"font-size:13px;color:#1F2E47;font-style:italic;margin-top:8px;\">Far too old for the method: after tens of millions of years no carbon-14 remains to measure, so fossils like this are dated from the rocks around them.<\/figcaption>\n<\/figure>\n\n<h3>What Carbon Dating Is Genuinely Used For<\/h3>\n\n<p>Strip away the myths and a solid list remains. Archaeology and museum conservation use it to place organic finds \u2014 charcoal, bone, textile, seed \u2014 in sequence. Forensic scientists use the post-1950 bomb rise to say whether recent remains grew before or after the testing era.<\/p>\n\n<p>It also works as a tracer rather than as a date, and not only on carbon that was once inside an organism. Hydrologists use carbon-14 to estimate how long groundwater has been underground, oceanographers use it to follow deep circulation, and conservators use it to check whether a supposedly old organic material is in fact modern.<\/p>\n\n<h2>Worked Problems<\/h2>\n\n<div class=\"pf-problem\"><div class=\"pf-problem-num\">Problem 1<\/div><div class=\"pf-problem-question\">A piece of charcoal measures 50.0 percent of modern carbon, against a starting level assumed to be the 1950 standard of 100. Using a half-life of 5700 years, what is its radiocarbon age?<\/div><details><summary>Show Solution<\/summary><div class=\"pf-problem-solution\">\n\n<strong>Solution:<\/strong>\n\nStep 1: Use t = (t\u00bd \/ ln 2) \u00d7 ln(N<sub>0<\/sub> \/ N). Write it as age = -\u03c4 \u00d7 ln(f), where f = N\/N<sub>0<\/sub> is the fraction of the original carbon-14 still present and \u03c4 = t\u00bd \/ ln 2 is the mean lifetime.\n\nStep 2: f = 50.0 \/ 100 = 0.5, and \u03c4 = 5700 \/ ln 2 = 8223.3617 years.\n\nStep 3: ln(0.5) = -0.6931472, so age = -8223.3617 \u00d7 (-0.6931472) = 5700.00 years.\n\n<strong>Answer: 5,700 radiocarbon years BP on the 5,700-year half-life.<\/strong> Half the carbon-14 gone means exactly one half-life elapsed, which is the one case you can check without a calculator.\n\n<\/div><\/details><\/div>\n\n<div class=\"pf-problem\"><div class=\"pf-problem-num\">Problem 2<\/div><div class=\"pf-problem-question\">The same laboratory reports 25.0 percent of modern carbon, with an uncertainty of 0.5 percent of the reading. On the 5700-year half-life, what is the age and its one-standard-deviation range?<\/div><details><summary>Show Solution<\/summary><div class=\"pf-problem-solution\">\n\n<strong>Solution:<\/strong>\n\nStep 1: age = -\u03c4 \u00d7 ln(f) again, with \u03c4 = 8223.3617 years.\n\nStep 2: f = 25.0 \/ 100 = 0.25 and ln(0.25) = -1.3862944, so age = 8223.3617 \u00d7 1.3862944 = 11400.00 years.\n\nStep 3: Take the two ends of the reading. 25.0 \u00d7 1.005 = 25.125 pMC gives 11358.9856 years; 25.0 \u00d7 0.995 = 24.875 pMC gives 11441.2199 years. Half that spread is (11441.2199 &#8211; 11358.9856) \/ 2 = 41.117 years.\n\n<strong>Answer: 11,400 radiocarbon years BP, \u00b1 41 years.<\/strong> Apply the same \u00b1 0.5 % to Problem 1 and you get \u00b1 41 years there too: the error bar in years depends on the mean lifetime and the relative precision, not on the age.\n\n<\/div><\/details><\/div>\n\n<div class=\"pf-problem\"><div class=\"pf-problem-num\">Problem 3<\/div><div class=\"pf-problem-question\">A sample reads 25.0 percent of modern carbon. What age do the Libby 5568-year, the current 5700-year and the Cambridge 5730-year half-lives each give, and how far apart are the answers?<\/div><details><summary>Show Solution<\/summary><div class=\"pf-problem-solution\">\n\n<strong>Solution:<\/strong>\n\nStep 1: age = -(T \/ ln 2) \u00d7 ln(0.25) for each half-life T, with ln(0.25) = -1.3862944 the same in all three.\n\nStep 2: T = 5568 gives 11136.00 years; T = 5700 gives 11400.00 years; T = 5730 gives 11460.00 years.\n\nStep 3: The spread is 11460.00 &#8211; 11136.00 = 324.00 years, and 324 \/ 11136 = 0.029095, i.e. 2.9095 % of the Libby age.\n\n<strong>Answer: 11,140, 11,400 and 11,460 radiocarbon years BP.<\/strong> The three scale by a fixed ratio, 5730\/5568 = 1.0290948, at every reading: 11136.00 \u00d7 1.0290948 = 11460.00. A radiocarbon age without a stated half-life is 324 years ambiguous here, and proportionally ambiguous everywhere.\n\n<\/div><\/details><\/div>\n\n<div class=\"pf-problem\"><div class=\"pf-problem-num\">Problem 4<\/div><div class=\"pf-problem-question\">A piece of wood grown in the early 1900s measures 98.0 percent of modern carbon. The atmosphere held 98 percent when it grew. On the 5700-year half-life, what age does it give on its own atmosphere, and what age if you assume the 1950 level of 100?<\/div><details><summary>Show Solution<\/summary><div class=\"pf-problem-solution\">\n\n<strong>Solution:<\/strong>\n\nStep 1: The fraction is the measured level divided by the level the wood actually started with, not by 100 out of habit.\n\nStep 2: On its own atmosphere, f = 98.0 \/ 98 = 1, and ln(1) = 0, so the age is 0 years.\n\nStep 3: Assume 100 instead and f = 98.0 \/ 100 = 0.98. Then ln(0.98) = -0.0202027, so age = 8223.3617 \u00d7 0.0202027 = 166.13 years.\n\n<strong>Answer: 0 radiocarbon years BP on its own atmosphere, and about 170 radiocarbon years BP if you assume the 1950 level.<\/strong> The wood is not old. The atmosphere was different, and this is exactly the error a calibration curve exists to remove.\n\n<\/div><\/details><\/div>\n\n<div class=\"pf-problem\"><div class=\"pf-problem-num\">Problem 5<\/div><div class=\"pf-problem-question\">A plant sample measures 150.0 percent of modern carbon against the 1950 standard. What radiocarbon age does the equation return on the 5700-year half-life, and what does that answer mean?<\/div><details><summary>Show Solution<\/summary><div class=\"pf-problem-solution\">\n\n<strong>Solution:<\/strong>\n\nStep 1: Nothing changes in the method; f is simply greater than 1.\n\nStep 2: f = 150.0 \/ 100 = 1.5 and ln(1.5) = 0.4054651.\n\nStep 3: age = -8223.3617 \u00d7 0.4054651 = -3334.29 years.\n\n<strong>Answer: -3,330 radiocarbon years BP, a negative age.<\/strong> It is not an arithmetic slip. The plant holds more carbon-14 than the 1950 atmosphere did, so it grew after 1950 \u2014 the fingerprint of the weapons-testing rise.\n\n<\/div><\/details><\/div>\n\n<div class=\"pf-problem\"><div class=\"pf-problem-num\">Problem 6<\/div><div class=\"pf-problem-question\">A sample reads 1.0 percent of modern carbon, but 1 percent of its carbon is modern contamination picked up during handling. On the 5700-year half-life, how much does that shift the age, and what would the same 1 percent do to a sample reading 50.0 percent?<\/div><details><summary>Show Solution<\/summary><div class=\"pf-problem-solution\">\n\n<strong>Solution:<\/strong>\n\nStep 1: Mix the two carbons by fraction: measured level = 0.99 \u00d7 (true level) + 0.01 \u00d7 100.\n\nStep 2: For the old sample, 1.0 \u00d7 0.99 + 100 \u00d7 0.01 = 0.99 + 1 = 1.99 pMC. Then ln(0.0199) = -3.9170355, so age = 8223.3617 \u00d7 3.9170355 = 32211.20 years, against 37869.98 years for a clean 1.0 pMC reading.\n\nStep 3: Rounded to the nearest ten, that is 32,210 against 37,870: the contamination makes the sample look 37,870 &#8211; 32,210 = 5,660 years younger.\n\nStep 4: Repeat at 50.0 pMC. The measured level is 50 \u00d7 0.99 + 100 \u00d7 0.01 = 50.5 pMC, giving 5,620 years against 5,700 years.\n\n<strong>Answer: 5,660 years too young at 1.0 pMC, but only 80 years too young at 50.0 pMC.<\/strong> The same 1 % of modern carbon does seventy times more damage to the old sample, which is why clean sampling matters most where the signal is faintest.\n\n<\/div><\/details><\/div>\n\n<div class=\"pf-problem\"><div class=\"pf-problem-num\">Problem 7<\/div><div class=\"pf-problem-question\">Work the formula backwards. What carbon-14 level would a sample that died 20,000 radiocarbon years ago show today, on the 5700-year half-life? How sensitive is that answer to the reading?<\/div><details><summary>Show Solution<\/summary><div class=\"pf-problem-solution\">\n\n<strong>Solution:<\/strong>\n\nStep 1: Rearranged for the level, N = N<sub>0<\/sub> \u00d7 e<sup>-t\/\u03c4<\/sup>, with \u03c4 = 8223.3617 years and N<sub>0<\/sub> = 100.\n\nStep 2: -20000 \/ 8223.3617 = -2.4320954, and e<sup>-2.4320954<\/sup> = 0.0878526.\n\nStep 3: N = 100 \u00d7 0.0878526 = 8.78526, which is 8.79 pMC to three significant figures.\n\n<strong>Answer: about 8.79 percent of modern carbon.<\/strong> For sensitivity, 8.8 pMC gives 19986.21 radiocarbon years and 8.9 pMC gives 19893.29, so 0.1 pMC is worth 92.92 years here, and the two ages are reported as 19,990 and 19,890. Make the same 0.1 pMC move at the faint end and the ages are 47770.68 at 0.3 pMC and 51104.97 at 0.2 pMC: the same step is worth 3334.29 years there.\n\n<\/div><\/details><\/div>\n\n<h2>Frequently Asked Questions<\/h2>\n\n<details class=\"pf-faq-item\"><summary>How does carbon dating work?<\/summary><div class=\"pf-faq-item-answer\">\n\nCarbon dating works by measuring how much carbon-14 is left in something that was once alive. Living things hold carbon-14 at the atmospheric level because they keep exchanging carbon with the air. Death stops the exchange, and the carbon-14 then decays with a half-life near 5,700 years, so the surviving fraction gives the time since death.\n\n<\/div><\/details>\n\n<details class=\"pf-faq-item\"><summary>What is the half-life of carbon-14?<\/summary><div class=\"pf-faq-item-answer\">\n\nThree values are in use, and each has a job. About 5,700 years is the currently recommended figure. The Cambridge value of 5,730 years is common in textbooks and is our calculator default. The original Libby value of 5,568 years is still used for reported radiocarbon ages so that old and new dates stay comparable. Always say which one you used.\n\n<\/div><\/details>\n\n<details class=\"pf-faq-item\"><summary>How far back can carbon dating go?<\/summary><div class=\"pf-faq-item-answer\">\n\nAbout 50,000 years, and the limit comes from measurement rather than from the equation. At that age a sample holds only two or three tenths of one percent of modern carbon, where laboratory background and any trace of modern contamination are as large as the signal itself. It is a working horizon, not a sharp cut-off.\n\n<\/div><\/details>\n\n<details class=\"pf-faq-item\"><summary>Can carbon dating be used on rocks or dinosaur bones?<\/summary><div class=\"pf-faq-item-answer\">\n\nNo. Carbon dating only works on material that once exchanged carbon with the atmosphere, which rules out rocks entirely. A dinosaur fossil is roughly 11,600 carbon-14 half-lives past death, leaving nothing measurable behind. Fossils and rocks are dated instead with isotope systems whose half-lives run to hundreds of millions or billions of years.\n\n<\/div><\/details>\n\n<details class=\"pf-faq-item\"><summary>What does BP mean in a radiocarbon date?<\/summary><div class=\"pf-faq-item-answer\">\n\nBP means &#8220;before present&#8221;, and by international convention the present is fixed at 1950. A date of 11,400 years BP therefore means 11,400 radiocarbon years before 1950, computed on a stated half-life and assuming the atmosphere always held the 1950 carbon-14 level. Turning that into a calendar date needs a published calibration curve.\n\n<\/div><\/details>\n\n<details class=\"pf-faq-item\"><summary>Why do laboratories still use a half-life they know is not the best value?<\/summary><div class=\"pf-faq-item-answer\">\n\nBecause consistency is worth more than accuracy here. Reported radiocarbon ages are computed with the Libby 5,568-year value so that a date published decades ago can be compared directly with one published today. The difference is not ignored; the calibration step absorbs it when the radiocarbon age is turned into a calendar date.\n\n<\/div><\/details>\n\n<details class=\"pf-faq-item\"><summary>How accurate is carbon dating?<\/summary><div class=\"pf-faq-item-answer\">\n\nPrecision and accuracy are different questions here. A measurement good to 0.5 percent of the reading gives an error bar of about 41 years at any age, which is the precision. Accuracy depends on whether the starting carbon-14 level was what you assumed, on reservoir effects, and on contamination \u2014 which can shift an old date by thousands of years.\n\n<\/div><\/details>\n","protected":false},"excerpt":{"rendered":"<p>Carbon dating measures how much carbon-14 is left in something that was once alive, and infers how long ago it died: t = (t-half \/ ln 2) x ln(N0 \/ N). The formula, the three half-lives, why a radiocarbon year is not a calendar year, what ruins a date, seven worked problems and an interactive lab.<\/p>\n","protected":false},"author":1,"featured_media":1909,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[203],"tags":[],"class_list":["post-1905","post","type-post","status-publish","format-standard","has-post-thumbnail","hentry","category-nuclear-physics"],"_links":{"self":[{"href":"https:\/\/physicsfundamentalsinfo.com\/blog\/wp-json\/wp\/v2\/posts\/1905","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/physicsfundamentalsinfo.com\/blog\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/physicsfundamentalsinfo.com\/blog\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/physicsfundamentalsinfo.com\/blog\/wp-json\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/physicsfundamentalsinfo.com\/blog\/wp-json\/wp\/v2\/comments?post=1905"}],"version-history":[{"count":4,"href":"https:\/\/physicsfundamentalsinfo.com\/blog\/wp-json\/wp\/v2\/posts\/1905\/revisions"}],"predecessor-version":[{"id":1978,"href":"https:\/\/physicsfundamentalsinfo.com\/blog\/wp-json\/wp\/v2\/posts\/1905\/revisions\/1978"}],"wp:featuredmedia":[{"embeddable":true,"href":"https:\/\/physicsfundamentalsinfo.com\/blog\/wp-json\/wp\/v2\/media\/1909"}],"wp:attachment":[{"href":"https:\/\/physicsfundamentalsinfo.com\/blog\/wp-json\/wp\/v2\/media?parent=1905"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/physicsfundamentalsinfo.com\/blog\/wp-json\/wp\/v2\/categories?post=1905"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/physicsfundamentalsinfo.com\/blog\/wp-json\/wp\/v2\/tags?post=1905"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}