3.10 Radioactive Dating and Half-Life

Radioactive Dating
and Half-Life

Word Cloud

What is radioactivity? (What is the first word that comes to mind?)

Complete the
notes on pages
47 and 48 in your
Earth Science
Notebook

Petrified
Wood

Radioactive elements in
rocks can be used to
determine the absolute
age of the rock

There are some
everyday
objects from
which a Geiger
counter can
detect low
levels of
radiation.

• A Geiger counter is adevice that detects radiation and can be used to identify and measure the levels of various
radioactive materials.

Radioactive
Decay

• In the early 1900s,

scientists began to study
radioactive materials. They
established fundamental
principles regarding
radioactive decay, the
process by which an
unstable atomic nucleus
releases energy in the form
of radiation.

Multiple Choice

Which of the
following best describes
an unstable nucleus of
an isotope?

• 
  equal numbers of electrons and protons

• 
  equal number of neutrons and electrons

• 
  extra electrons

• 
  extra neutrons, packed especially tight

Radiometric Dating and Half-life

The time it takes for a radioactive isotope to decay is measured using a term called half-life.

The half-life of a radioactive substance is the time it takes for half of its unstable atoms to break
down into daughter products.

Isotopes that are extremely unstable decay quickly

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Multiple Choice

Which of the following best defines the term half-life in the context of radioactive decay?

• 
  the time it takes for radioactive emissions in a sample to run out

• 
  the time it takes for all the radioactive atoms in a sample to decay completely

• 
  the time it takes for a radioactive substance to become stable

• the time it takes for half of the radioactive atoms in a sample to undergo transformation

Radiometric Dating and
Geology

• Radiometric dating is widely

used in geology to determine the
ages of rocks, fossils, and
geological events.

Uranium-lead dating

Uranium-lead dating is a form of radiometric dating that uses elements with longer half-lives such as uranium, that lead to more accurate measurements of age.

Multiple Choice

Radiometric dating is a valuable tool in geology for determining the ages of various geological materials. Which of the following statements best describes the role of radiometric dating?

• 
  Radiometric dating measures the current temperature of rocks and minerals.

• 
  Radiometric dating helps estimate the ages of rocks, fossils, and geological formations.

• 
  Radiometric dating is primarily used to predict future geological events.

• 
  Radiometric dating determines the chemical composition of Earth's atmosphere.

Radiometric Dating Living vs. Non-Living
Material

• Carbon-14 dating is suitable fordating materials that were once part of the carbon cycle, such as once-living remains.

• It is widely used for archaeological purposes, dating artifacts, fossils, and ancient organic materials.

• Due to the length of carbon-14’s half-life, this isotope is accurate for
determining the age of organic
material upwards to 55,000 years old.

Multiple Choice

For dating a wooden tool recovered from an archaeological site, which radioactive isotope would be most suitable?

• 
  uranium-238

• potassium-40

• 
  carbon-14

• rubidium-87

Advantages and Limitations of Radioactive Dating

Multiple Choice

Which statement about unstable isotopes is accurate regarding dating rocks and fossils?

• crucial because radioactive decay provides a measurable way to estimate the age of rocks and fossils.

• not essential; stable isotopes are needed for absolute dating of the age of rocks and fossils

• only useful for dating once-living materials, but not rocks or fossils

Multiple Choice

A scientist wants to determine the age of an ancient wood beam once used for a lodge. Which explanation best describes why radioactive dating is the process to use?

• The radioactive isotope in the wood beam is gradually replaced by a stable isotope, and by comparing initial and current ratios, the scientist can estimate the age of the lodge.

• The radioactive isotope in the beam transforms into a completely new radioactive element after it decays. The new element's presence indicates the age of the lodge.

  
  

• The radioactive isotope is directly correlated with its weight, as heavier wood is considered older.

  
  

Multiple Choice

Why is carbon-14 not typically used for materials older than about 55,000 years old?

• Objects older than that have no carbon-14

• 
  After 55,000 years they decay happens too rapidly to measure

• 
  After 55,000 years there is very little carbon-14 to measure accurately.

Today, we
learned about:

• the concept of

radioactive decay;

• how various

radioactive isotopes
are used in different
dating methods; and

• some strengths and

limitations of
radioactive dating in
Earth Science
research.