Carbon dating exam questions
Since the atmosphere is composed of about 78 percent nitrogen,2 a lot of radiocarbon atoms are produced—in total about 16.5 lbs. These rapidly combine with oxygen atoms (the second most abundant element in the atmosphere, at 21 percent) to form carbon dioxide (CO This carbon dioxide, now radioactive with carbon-14, is otherwise chemically indistinguishable from the normal carbon dioxide in the atmosphere, which is slightly lighter because it contains normal carbon-12.
So one would think that since the radiocarbon dating method works on organic (once-living) materials, then radiocarbon could be used to date fossils.It’s assumed to be the same number of carbon-14 atoms as in elephants living today.With time, those sand grains fell to the bottom bowl, so the new number represents the carbon-14 atoms left in the mammoth skull when we found it.Radiocarbon (carbon-14 or C) forms continually today in the earth’s upper atmosphere.And as far as we know, it has been forming in the earth’s upper atmosphere at least since the Fall, after the atmosphere was made back on Day Two of creation week (part of the expanse, or firmament, described in Genesis 1:6–8). Cosmic rays from outer space are continually bombarding the upper atmosphere of the earth, producing fast-moving neutrons (sub-atomic particles carrying no electric charge) (figure 1).1 These fast-moving neutrons collide with nitrogen-14 atoms, the most abundant element in the upper atmosphere, converting them into radiocarbon (carbon-14) atoms.Through photosynthesis carbon dioxide enters plants and algae, bringing radiocarbon into the food chain.
Radiocarbon then enters animals as they consume the plants (figure 2).
So if half the sand grains are in the top bowl and half in the bottom bowl, then 30 minutes has elapsed since the sand grains began falling.
We can calibrate an hourglass clock by timing the falling sand grains against a mechanical or electronic clock.
(This 5,730 year period is called the half-life of radiocarbon, figure 5).6 At this decay rate, hardly any carbon-14 atoms will remain after only 57,300 years (or ten half-lives). The decay of radiocarbon follows the exponential decay law, whereby the percentage decrease in the number of parent atoms per unit time is constant.
After each half-life of 5,730 years, the number of parent radiocarbon atoms remaining is halved.
The difference in the number of sand grains represents the number of carbon-14 atoms that have decayed back to nitrogen-14 since the mammoth died. The sand grains in the top bowl fall to the bottom bowl to measure the passage of time.