Carbon dating explained simply la dating ideas
However it is possible, when dating very old rocks for instance, to use longer lived isotopes for dating on a longer time scale.3) The assumption we based this on (that the ratio of carbon 14 in the atmosphere and thus in living organisms is constant) is a decent one for ballpark figures, but this method will not be able to give results accurate to, say, a couple of minutes.Because the cosmic ray bombardment is fairly constant, there’s a near-constant level of carbon-14 to carbon-12 ratio in Earth’s atmosphere.Organisms at the base of the food chain that photosynthesize – for example, plants and algae – use the carbon in Earth’s atmosphere.The unstable carbon-14 gradually decays to carbon-12 at a steady rate. Scientists measure the ratio of carbon isotopes to be able to estimate how far back in time a biological sample was active or alive.This plot shows the level of carbon-14 in the atmosphere as measured in New Zealand (red) and Austria (green), representing the Southern and Northern Hemispheres, respectively.Asked by: William Baker Carbon 14 (C14) is an isotope of carbon with 8 neutrons instead of the more common 6 neutrons.
Carbon 14 dating is not great for dating things like a year old because if much less than 1 half-life has passed, barely any of the carbon 14 has decayed, and it is difficult to measure the difference in rates and know with certainty the time involved.
We have devices to measure the radioactivity of a sample, and the ratio described above translates into a rate of 15.6 decays/min per gram of carbon in a living sample.
And if you play with the exponential decay equations, you can come up with the nice formula (1/2)=(current decay rate)/(initial decay rate), where n is the number of half lives that have passed.
It’s not absolutely constant due to several variables that affect the levels of cosmic rays reaching the atmosphere, such as the fluctuating strength of the Earth’s magnetic field, solar cycles that influence the amount of cosmic rays entering the solar system, climatic changes and human activities.
Among the significant events that caused a temporary but significant spike in the atmospheric carbon-14 to carbon-12 ratio were above-ground nuclear test detonations in the two decades following World War II.