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Film fossils form where leaves have left black or brown marks, made of carbon, on rock surfaces. A film fossil of a leaf is shown in Figure 4.

A film fossil of a leaf

Fossil dating

Radiometric dating

Radiometric dating is sometimes used when scientists want to date fossils. Some elements are unstable and break down into lighter elements over time. Suchsubstances are said to be radioactive. The original element is called the parent and the element it changes into is called the daughter. For example,uranium-238 decays into lead-206. What is the data which scientists use in this method, and the assumptions they might make when drawing conclusions aboutfossil dates?:

Data: A rock has a certain ratio of the parent to daughter elements, e.g. a certain ratio of uranium to lead.
Conclusions: In radiometric dating, the ratio of parent to daughter elements is compared. From this the age of the rock is concluded.
Assumptions: A scientist has to make many assumptions in order to conclude the age of a rock from ratios between elements. These assumptions include:

The rock must have had only parent, and no daughter, elements when the rock formed.
The rate at which the parent element changed into the daughter element is known from the rate this occurs today.
For example, if a rock is found containing both uranium-238 and lead-206, it is assumed that all this lead came from the uranium by radioactive decay and thatthe rate at which that happened is the same as the rate observed today.

Carbon dating

Carbon dating is the only type of radiometric dating which can be done directly on fossils. However, carbon dating gives young ages, and so is generally notaccepted, except for dating organisms which have been dead for less than about 30 000 years.

How does carbon dating work? All organisms incorporate carbon atoms into their bodies when they are alive. This stops at death. There are two isotopes (forms)of carbon. The most common isotope is C12. The other isotope, C14, is radioactive. The proportion C12:C14 in the atmosphere is known. Both carbonisotopes combine with oxygen to form CO2 and both are incorporated into plants during photosynthesis. Therefore both carbon isotopes form part ofanimals’ food. The organism dies. The C12 in the dead body does not break down radioactively, but the C14 in the body does break down radioactively. Wecan measure the rate at which C14 breaks down radioactively over time today. Scientists compare the ratio of C12:C14in the body to the ratio of C12:C14inthe atmosphere. This is the data used. The scientists may assume that the C12:C14 ratio at the time of death was the same as the atmosphere’sC12:C14ratio, and that the rate at which C14broke down in the past was the same as it is today. From this they may conclude the age of the rock.

Dating fossils by dating rocks

For fossils which are believed to be older than 30 000 years, carbon dating cannot be used, so other radiometric dating methods are used. However, thesemethods can only be done on igneous rocks (rocks formed from volcanoes).Igneous rock cannot contain fossils. Fossils are only found in sedimentary rock. Inorder to conclude the date of a fossil the following process is followed:

Questions & Answers

what is variations in raman spectra for nanomaterials
Jyoti Reply
I only see partial conversation and what's the question here!
Crow Reply
what about nanotechnology for water purification
RAW Reply
please someone correct me if I'm wrong but I think one can use nanoparticles, specially silver nanoparticles for water treatment.
yes that's correct
I think
what is the stm
Brian Reply
is there industrial application of fullrenes. What is the method to prepare fullrene on large scale.?
industrial application...? mmm I think on the medical side as drug carrier, but you should go deeper on your research, I may be wrong
How we are making nano material?
what is a peer
What is meant by 'nano scale'?
What is STMs full form?
scanning tunneling microscope
how nano science is used for hydrophobicity
Do u think that Graphene and Fullrene fiber can be used to make Air Plane body structure the lightest and strongest. Rafiq
what is differents between GO and RGO?
what is simplest way to understand the applications of nano robots used to detect the cancer affected cell of human body.? How this robot is carried to required site of body cell.? what will be the carrier material and how can be detected that correct delivery of drug is done Rafiq
what is Nano technology ?
Bob Reply
write examples of Nano molecule?
The nanotechnology is as new science, to scale nanometric
nanotechnology is the study, desing, synthesis, manipulation and application of materials and functional systems through control of matter at nanoscale
Is there any normative that regulates the use of silver nanoparticles?
Damian Reply
what king of growth are you checking .?
What fields keep nano created devices from performing or assimulating ? Magnetic fields ? Are do they assimilate ?
Stoney Reply
why we need to study biomolecules, molecular biology in nanotechnology?
Adin Reply
yes I'm doing my masters in nanotechnology, we are being studying all these domains as well..
what school?
biomolecules are e building blocks of every organics and inorganic materials.
anyone know any internet site where one can find nanotechnology papers?
Damian Reply
sciencedirect big data base
Introduction about quantum dots in nanotechnology
Praveena Reply
what does nano mean?
Anassong Reply
nano basically means 10^(-9). nanometer is a unit to measure length.
do you think it's worthwhile in the long term to study the effects and possibilities of nanotechnology on viral treatment?
Damian Reply
absolutely yes
how did you get the value of 2000N.What calculations are needed to arrive at it
Smarajit Reply
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why and for what was five kingdom of classification of organisms introduced
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Comment on the ozone depletion over the period of 1982 to 1996
Mpho Reply

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Source:  OpenStax, Siyavula: life sciences grade 10. OpenStax CNX. Apr 11, 2012 Download for free at http://cnx.org/content/col11410/1.3
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