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Unit 1 Radiometric Dating
Listening Comprehension
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. For this reason,
it is a vital tool for those studying the evolution of species or the ancient origins of man. In this
method, scientists measure the decay of carbon-14, a radioactive isotope of carbon. Carbon
dating is an ideal method for dating organically based specimens because carbon is an intrinsic
part of every organism‘s life cycle. Through the processes of respiration and digestion, living
organisms are constantly taking in carbon-based molecules. 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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Listening Comprehension
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. For this reason,
it is a vital tool for those studying the evolution of species or the ancient origins of man. In this
method, scientists measure the decay of carbon-14, a radioactive isotope of carbon. Carbon
dating is an ideal method for dating organically based specimens because carbon is an intrinsic
part of every organism‘s life cycle. Through the processes of respiration and digestion, living
organisms are constantly taking in carbon-based molecules. 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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