If the half life of C is 5780 years why does C exist today on earth? Why is C generally not used for dating in

Question

geology ?

What is used for dating rocks and events in geology?

Answer 1

New radioactive carbon is incorporated into living things all the time (through respiration). When you die, no more radioactive carbon is incorporated, and the radioactive carbon that was in you when you died starts to decay. That's how scientists can tell how long ago you died. Only things that were previously living can be dated by carbon dating.

Answer 2

Thank you for asking a hard question! If left to its own devices, the planet would have run out of carbon 14 quite some time ago. However, the atmosphere is full of nitrogen-14. A cosmic ray strike in the upper atmosphere can chan cause positron decay, resulting in a transformation from nitrogen-14 to carbon-14. It continually rains carbon-14 in small amounts. Lifeforms that are dead and buried no longer absorb any carbon. All the carbon-14 decays over time. They can use this to figure out how old long its been since an organism was exposed to this sort of carbon, and hence how long its been buried.

http://hyperphysics.phy-astr.gsu.edu/hbase/nuclear/cardat.html

However, this doesn't work well for geology. Rocks don't absorb much ambient carbon on their own, unlike animals or plants. They also tend to be extremely old, so old they often no longer contain any carbon-14 at all.

For geology, you need uranium. Uranium has a much longer half-life (U-238's is approximately 4.46 billion years, or about the current age of the Earth). The final breakdown product of decaying uranium-238 is lead-209. Some minerals contain uranium but do not naturally contain any lead and most lead isn't lead-209, so the ratio of lead-209 to uranium-238 can be used to make a pretty good guess at the age of a rock formation. There are other sorts of radioactive dating, but they all follow the same basic principle.

Wiki is useful on this topic if you are curious:
http://en.wikipedia.org/wiki/Uranium-lead_dating

Answer 3

The half life you refer to is for carbon 14 which makes up only a small portion of the total amount of carbon on Earth. Most carbon is carbon 12 which is stable.

So why is their any carbon 14 left? Carbon binds with oxygen to form carbon dioxide, a gas, which floats around in the atmosphere. A portion of this carbon dioxide rises into the upper atmosphere where it is bombarded by radiation from space. This radiation can convert some of the carbon 12 to carbon 14 (or perhaps other elements are converted to carbon 14.) In any case space radiation keeps the proportion of carbon 14 in the atmosphere fairly constant. When carbon gets trapped in something solid like a tree trunk then its proportion of carbon 14 decreases due to its half life. Unlike the upper atmosphere there is no process to make more. That is the basis for carbon dating. The less carbon 14 there is in a sample the older it is. But after several half lives the amount of carbon 14 gets so small that the dates become unreliable.

Recently work was done to compare tree ring dates to carbon 14 dates and it was found that during certain periods there must have been more carbon 14 created than usual, probably due to peaks in solar activity. This required that archaeologists revise a lot of their dates and therefore their theories about the spread of early people and their technology.

Answer 4

it form of feels that we attain a undeniable age of adulthood, in spite of the type, as quickly as we know that there's no longer something we are able to do to have a important impression interior the international. We settle into the convenience of being who we are with like me or do no longer ideas-set, and existence strikes onward. those Golden years can incorporate the know-how of many lives on the ripe age of a teenager or as quickly as we've finished our important paintings and might get exhilaration from the advantages. we are able to observe the youngsters respond to what we've taught them; it extremely is magical. you're at peace, and could no longer le everyone take it from you. you may supply it up when you consider which you care approximately somebody extra suitable than your self, even if it extremely is a private decision. it extremely is a attractive poem. Mellow and non violent. thank you for sharing it.

Answer 5

Half life of carbon you are referring is not of C 12 but it is of C 14.
And let me make you clear that half given is not linear half life it is in fact logarithmic. Suppose you have 1 kg of C14, after 5780 years only half kg is left ; you are right.. But remaining half kg will not be finished in another 5780 years. Thats the point. In another 5780 years half of that half kg is finished and in another 5780 years half of half of half kg will be finished and it will never reach zero level. ( in logarithmic system zero is not attainable).
More over new C14 may form from other radioactive metal too which does not let its level to decrease to zero level.