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Unit 1 Radiometric Dating
Reading Comprehension
Radiometric Dating
A primary difficulty in any science which seeks to illuminate the past — be it archeology,
anthropology, paleontology, or geology — is the need to establish firm and accurate dates for
various pieces of evidence. If a paleontologist wishes to understand the evolutionary path of a
certain species, then he or she must be able to date fossils of that species with precision.
Similarly, geologists wishing to understand the early stages of the earth‘s formation need to be
able to establish a timeline for the formation of various rock structures. Over the past century,
scientists have established a number of methodologies to assist in such dating. One of the
most productive is radiometric dating.
Radiometric dating relies on the presence of radioactive isotopes, such as carbon-14 and
unranium-235, which are locked within the various rocks and fossils that scientists wish to
date. Over time, these isotopes decay into more stable atoms, and this radioactive decay
occurs at a steady and predictable rate. Thus, by measuring the amount of radioactive decay
that has already taken place in a particular sample, scientists are able to arrive at a reasonable
estimate for its age. There are two primary methods of radiometric dating, carbon dating and
uranium-lead dating, and each has specific uses.
Carbon dating, first developed by Willard Libby of the Institute for Nuclear Studies in 1947, is
used exclusively in the dating of organic materials, such as fossils and bones. [A] In this
method, scientists measure the decay of carbon-14, a radioactive isotope of carbon. [B]
Carbon dating is an ideal method for dating organically based specimens because carbon is an
intrinsic part of every organism‘s life cycle. [C] Through the processes of respiration and
digestion, living organisms are constantly taking in carbon-based molecules. [D] These
molecules have a predictable ratio of radioactive carbon-14 isotopes and the more stable
carbon-12 atoms. As long as the organism is breathing and eating (i.e., living), the ratio of
these two forms of carbon remains stable, because the organism is constantly taking in new
carbon-based molecules. However, when these vital life processes cease, no new carbon is
incorporated into the organism‘s tissues. As the radioactive carbon-14 begins to decay, the
ratio between carbon-14 and carbon-12 changes. By comparing the ratio of these atoms in a
fossil to the ratio one would expect to find in a living creature, scientists can arrive at a fairly
accurate estimate for the time of the creature‘s death.
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Reading Comprehension
Radiometric Dating
A primary difficulty in any science which seeks to illuminate the past — be it archeology,
anthropology, paleontology, or geology — is the need to establish firm and accurate dates for
various pieces of evidence. If a paleontologist wishes to understand the evolutionary path of a
certain species, then he or she must be able to date fossils of that species with precision.
Similarly, geologists wishing to understand the early stages of the earth‘s formation need to be
able to establish a timeline for the formation of various rock structures. Over the past century,
scientists have established a number of methodologies to assist in such dating. One of the
most productive is radiometric dating.
Radiometric dating relies on the presence of radioactive isotopes, such as carbon-14 and
unranium-235, which are locked within the various rocks and fossils that scientists wish to
date. Over time, these isotopes decay into more stable atoms, and this radioactive decay
occurs at a steady and predictable rate. Thus, by measuring the amount of radioactive decay
that has already taken place in a particular sample, scientists are able to arrive at a reasonable
estimate for its age. There are two primary methods of radiometric dating, carbon dating and
uranium-lead dating, and each has specific uses.
Carbon dating, first developed by Willard Libby of the Institute for Nuclear Studies in 1947, is
used exclusively in the dating of organic materials, such as fossils and bones. [A] In this
method, scientists measure the decay of carbon-14, a radioactive isotope of carbon. [B]
Carbon dating is an ideal method for dating organically based specimens because carbon is an
intrinsic part of every organism‘s life cycle. [C] Through the processes of respiration and
digestion, living organisms are constantly taking in carbon-based molecules. [D] These
molecules have a predictable ratio of radioactive carbon-14 isotopes and the more stable
carbon-12 atoms. As long as the organism is breathing and eating (i.e., living), the ratio of
these two forms of carbon remains stable, because the organism is constantly taking in new
carbon-based molecules. However, when these vital life processes cease, no new carbon is
incorporated into the organism‘s tissues. As the radioactive carbon-14 begins to decay, the
ratio between carbon-14 and carbon-12 changes. By comparing the ratio of these atoms in a
fossil to the ratio one would expect to find in a living creature, scientists can arrive at a fairly
accurate estimate for the time of the creature‘s death.
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