<< Chapter < Page Chapter >> Page >

Art connection

Carbon is indicated by its atomic symbol, a capital C. Carbon has the atomic number six and two stable isotopes, carbon-12 and carbon-13.
Carbon has an atomic number of six, and two stable isotopes with mass numbers of twelve and thirteen, respectively. Its relative atomic mass is 12.011

How many neutrons do carbon-12 and carbon-13 have, respectively?

Isotopes

Isotopes are different forms of an element that have the same number of protons but a different number of neutrons. Some elements—such as carbon, potassium, and uranium—have naturally occurring isotopes. Carbon-12 contains six protons, six neutrons, and six electrons; therefore, it has a mass number of 12 (six protons and six neutrons). Carbon-14 contains six protons, eight neutrons, and six electrons; its atomic mass is 14 (six protons and eight neutrons). These two alternate forms of carbon are isotopes. Some isotopes may emit neutrons, protons, and electrons, and attain a more stable atomic configuration (lower level of potential energy); these are radioactive isotopes, or radioisotopes . Radioactive decay (carbon-14 losing neutrons to eventually become carbon-12) describes the energy loss that occurs when an unstable atom’s nucleus releases radiation.

Evolution connection

Carbon dating

Carbon is normally present in the atmosphere in the form of gaseous compounds like carbon dioxide and methane. Carbon-14 ( 14 C) is a naturally occurring radioisotope that is created in the atmosphere from atmospheric 14 N (nitrogen) by the addition of a neutron and the loss of a proton because of cosmic rays. This is a continuous process, so more 14 C is always being created. As a living organism incorporates 14 C initially as carbon dioxide fixed in the process of photosynthesis, the relative amount of 14 C in its body is equal to the concentration of 14 C in the atmosphere. When an organism dies, it is no longer ingesting 14 C, so the ratio between 14 C and 12 C will decline as 14 C decays gradually to 14 N by a process called beta decay—the emission of electrons or positrons. This decay gives off energy in a slow process.

After approximately 5,730 years, half of the starting concentration of 14 C will have been converted back to 14 N. The time it takes for half of the original concentration of an isotope to decay back to its more stable form is called its half-life. Because the half-life of 14 C is long, it is used to date formerly living objects such as old bones or wood. Comparing the ratio of the 14 C concentration found in an object to the amount of 14 C detected in the atmosphere, the amount of the isotope that has not yet decayed can be determined. On the basis of this amount, the age of the material, such as the pygmy mammoth shown in [link] , can be calculated with accuracy if it is not much older than about 50,000 years. Other elements have isotopes with different half lives. For example, 40 K (potassium-40) has a half-life of 1.25 billion years, and 235 U (Uranium 235) has a half-life of about 700 million years. Through the use of radiometric dating, scientists can study the age of fossils or other remains of extinct organisms to understand how organisms have evolved from earlier species.

Photo shows scientists unearthing a mammoth skeleton.
The age of carbon-containing remains less than about 50,000 years old, such as this pygmy mammoth, can be determined using carbon dating. (credit: Bill Faulkner, NPS)

Questions & Answers

Is the "growth and maintenance phase" in a cell's life cycle when cell division is about to occur
Somto Reply
what is the common name of Basidiomycetes
Ogechukwu Reply
الاجزاء النباتية لابد من تعقيمها قبل زراعتها في القوارير
yes
tariq
whats this?
tariq
do you speak arabic?!
what are bio elements
Shahzad Reply
which are present In Body And such elements Have Great role in our Body there are 16 bio elements that maintains human Body but on The basis of amount There are 6 bio elements present in Concen. of 99% and More Valuable And Highly Concen. element is Oxygent with 65 %
Haider
how je pollution brought about
Lamina Reply
how je pollution brouhgt about
Lamina
non is pollution brouhgt about
Lamina
describe the anatomy of cell division
Ivanovic Reply
Complex traits such as height result from 
Ruben Reply
what is the difference between chloroplasts and mitochondria
Nkalubo Reply
chloroplast in plants and bacterial cell ; mitochondria in animal cells
aung
Diagram of a living cell
Eliza Reply
what is cell
Sule
A cell is the smallest basic unit of life.
John
what's biology
Ogochukwu Reply
this is da study of living and non-living thing in an eco-system
Nutty
it is the study of living and non living organism in the ecology
Akufia
I agree with you dat biology is d study of living nd nonliving features
Winner
why do plants store carbohydrates in form of starch and not glucose?
Nutty Reply
Describe the structure of starch?
Nutty
wat is diffusion
Winner
water is life!.. Discuss?
Nutty Reply
why do plants store carbohydrates in form if starch not glucose!
Nutty
study of living thing
Dennis Reply
what is beyond a liveing cell
Raymond
what is biology
Gabriel Reply
d study of living nd non living thing
Winner
what is vasectomy
Evelyn Reply
The surgical removal of d spermduct
Eniola

Get the best Biology course in your pocket!





Source:  OpenStax, Biology. OpenStax CNX. Feb 29, 2016 Download for free at http://cnx.org/content/col11448/1.10
Google Play and the Google Play logo are trademarks of Google Inc.

Notification Switch

Would you like to follow the 'Biology' conversation and receive update notifications?

Ask