Download Ch.3, Sec.3 – Absolute Dating: A Measure of Time Radiometric Dating

Ch.3, Sec.3 – Absolute Dating: A
Measure of Time
- with the discovery of the natural decay
of uranium in 1896, French physicist
Henri Becquerel provided a means of
using radioactive elements as clocks to
measure geologic time
- the process of establishing the age of an
object by determining the number of
years it has existed is called absolute
dating
Henri Becquerel
Ch.3, Sec.3 – Absolute Dating: A
Measure of Time
 Radioactive Decay
- to determine the age of rocks & fossils, scientists analyze
isotopes of radioactive elements
- atoms of the same element that have the same number of
protons but have a different number of neutrons are called
isotopes
- radioactive isotopes tend to break
down into stable isotopes of the
same or other elements in a
process called radioactive decay
Ch.3, Sec.3 – Absolute Dating: A
Measure of Time
- the radioactive decay process of parent isotopes often times
creates daughter isotopes, which are stable elements
- the length of time it takes for elements to decay is always
constant, so scientists can compare the amount of parent
material to daughter material in rocks and fossils to date them
- the more daughter material there is, the older the rock or
fossil will be!
Ch.3, Sec.3 – Absolute Dating: A
Measure of Time
 Radiometric Dating
- determining the age of an object by estimating the relative
percentages of a radioactive (parent) isotope & a stable
(daughter) isotope is called radiometric dating
- scientists measure this age
by calculating the half-life,
which is the time needed for
half of a sample of a
radioactive substance to
undergo radioactive decay
Ch.3, Sec.3 – Absolute Dating: A
Measure of Time
 Types of Radiometric Dating
1. Potassium-Argon Method: potassium-40 has a half-life of
1.3 billion years & decays into calcium or argon (used to date
rocks & fossils older than 100,000 years)
2. Uranium-Lead Method: uranium-238 has a half-life of 4.5
billion years & decays into lead (used to date rocks & fossils
older than 10 million years)
3. Rubidium-Strontium Method: rubidium-87 has a half-life of
49 billion years & decays into strontium-87 (used to date rocks
& fossils older than 10 million years)
Ch.3, Sec.3 – Absolute Dating: A
Measure of Time
4. Carbon-14 Method: carbon-14 has a half-life of 5,730
years & decays into nitrogen-14 (used to date rocks & fossils
younger than 50,000 years old)