Radioactive Carbon Dating
When did life first appeared on earth? This is one of the most interesting questions that modern people have. I will tell you when history of life on Earth began. It is 3.8 billion years ago and it looked like this:
How people know all of such kind of stuff like when did life arose on Earth or the ages of ancient artifacts. The answer lies in the nature of organic compounds. They all have carbon in their structure. Carbon is the 4th most abundant chemical element in the universe by mass, with atomic number 6 which contains 6 protons, 6 neutrons and 6 electrons. However, there are two other naturally accruing isotopes of this element one of them C13 which contains 7 (13-6=7) neutrons and has 1.07% abundance unlike the C12 which forms remaining 98.93%. Second isotope is C14 containing 8 neutrons which is created from nitrogen atom when it is hit by cosmic rays. Cosmic rays in the form of energetic neutrons collide with N2 atoms containing 7 protons, 7 neutrons and form C14 isotope and a hydrogen atom (proton). It’s nuclear reaction formula will be like:
1n+14N→14C+1p
This isotope helps us to estimate the age of artifacts. Since, it has more neutrons its nucleus is unstable and has tendency to disintegrate or decay. Decaying isotopes emit radiation which is energy travelling as waves or particles. So C14 is radioactive, decaying with a half-life of about 5,730 years.
Half-life is the amount of time required for a quantity of anything to diminish to half its original value, as measured at the starting of the time. The amount of carbon-14 will devide into two each 5,730 years. Its graph will look like:
So, measuring the amount of C14 in the object gives us information about how old it is. C14 present in the macromolecules of our body, for example you eat the carbon-14 that was in the plant organism and before was in the atmosphere. The C14 atoms react with oxygen and form CO2 (carbon dioxide), which is absorbed by plants through photosynthesis forming glucose which then used for structure like fibers. Animals eat plants and absorb C14 also. So, the ratio of C12 to C14 in the atmosphere and in living organisms at any given time is nearly constant, because living things take in the same amount of carbon-14 that is constantly present in the atmosphere. As you keep eating your body has a certain ratio of C14 atoms in it, and all living plants and animals have the same ratio.
After death, organism it stops absorbing new carbon. The ratio of C12 to C14 can be used to determine the age, because the C14 starts decaying and is not replaced.
The carbon-14 decays with its half-life of 5,700 years, while the amount of carbon-12 remains constant in the sample. By looking at the ratio of carbon-12 to carbon-14 in the sample and comparing it to the ratio in a living organism, it is possible to determine the age of a formerly living thing fairly precisely. For more information about calculation using formula see this page.
Reference list:
BBC. "Archean era." BBC News. http://www.bbc.co.uk/nature/history_of_the_earth/Archean (accessed September 26, 2014).
