<< 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

what is biology
lilian Reply
what is biology
Dada Reply
The scientific study of life.
juanita
the virus that causes mumps in humans is composed of a protein outer Shell containing a core of DNA
Daniel Reply
Basic science and applied science question about cancer
Joyce Reply
what are the importance of ATPs
Olatunji Reply
How can biology be studied from a microscopic approach to a global approach
Joyce Reply
The large central opening in the poriferan body is called
Chynna Reply
You go for a long walk on a hot day. Give an example of a way in which homeostasis keeps your body healthy.
Joyce Reply
You sweat.
juanita
sweating is your bodies way of keeping you from overheating.
juanita
Thank you
Joyce
what is biology
Neya Reply
biology is the study of life
IYANUYIMIKA
Biology is the study of Life
Brianna
is the branch of science which deals with the of living things.
Peter
what is metabolism
Sangam Reply
hi palz, what's the ?
Gbolajobi Reply
hi plz, what's the.
Atta
pls come a again
Gyamfi
Describe the steps and results of reintroducing wolves to Yellowstone National Park.
Natalia Reply
tag and release wolves into Yellowstone. wolves eventually reproduce and the pack grows. as wolves hunt they cull the sick and weak prey. the carcass that is left provides food for other species (scavengers and insect.. etc). this heals the circle of life and contributes to the biodiversity...
Will
before you know it species that are critical to the eco system return. having apex predators is crucial to an ecosystem... it helps run the deer and elk , etc around.
Will
example: there was a species of shrub/ plant that grows along river banks that moose love to eat.. the moose have no predator so they decimate that food source which also helps prevent erosion. when the wolves were reintroduced this changed. oddly enough this plant species started to repopulate in
Will
the areas where wolf feces sat and decayed
Will
which of the following statements about the parts of an egg are false?
Israel Reply
Monotremes include...?
Israel
medicinal plants including microbs
vijay Reply
,medicinal plants including microbes
vijay
what is biology
Siyanbola Reply
study of living organisms...
R0se
study of plants and animals
Divine

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