Chapter 13 Chapter 13 Section 3Section 3

Absolute Ages of RocksAbsolute Ages of Rocks

Absolute AgeAbsolute Age

Absolute age is the age in Absolute age is the age in yearsyears of a of a rock or other object.rock or other object.

Absolute ageAbsolute age is determined by using is determined by using the properties of atoms that make up the properties of atoms that make up materials.materials.

Radioactive DecayRadioactive Decay

Atoms of the same element that have Atoms of the same element that have different numbers are called different numbers are called isotopesisotopes..

Isotopes are Isotopes are unstableunstable and can break and can break down. The process of this breaking down. The process of this breaking down is called down is called radioactive decayradioactive decay..

Half-lifeHalf-life

The The halfhalf--lifelife of an isotope is the time of an isotope is the time it takes for it takes for halfhalf of the atoms in the of the atoms in the isotope to decay.isotope to decay.

The The parentparent isotope goes through isotope goes through radioactive decay. The radioactive decay. The daughterdaughter product is produced from this decay. product is produced from this decay. The time it takes half of the parent The time it takes half of the parent isotope to decay into its daughter isotope to decay into its daughter product is the half-life of that isotope.product is the half-life of that isotope.

Radiometric DatingRadiometric Dating

By measuring the ratio of By measuring the ratio of parentparent isotope isotope to to daughter daughter product, and by knowing the product, and by knowing the halfhalf--lifelife of the parent, scientists can of the parent, scientists can calculate the absolute age or a rock.calculate the absolute age or a rock.

This process is called This process is called radiometric datingradiometric dating.. Carbon-14Carbon-14 dating is used to date bones, dating is used to date bones,

wood, and coal up to 75,000 years old. wood, and coal up to 75,000 years old. (half-life of carbon is 5,730 years.)(half-life of carbon is 5,730 years.)

Radiometric Dating Radiometric Dating continued…continued…

Potassium-AragonPotassium-Aragon dating is used to date dating is used to date rocks millions of years old (half-life of rocks millions of years old (half-life of potassium-40 is 1.25 billion years.)potassium-40 is 1.25 billion years.)

Dating is useful for Dating is useful for igneousigneous and and metamorphicmetamorphic rocks. rocks.

This dating is not useful for This dating is not useful for sedimentarysedimentary rocks, because they are made of pieces of rocks, because they are made of pieces of older rocks.older rocks.

The oldest rocks are The oldest rocks are 3.963.96 billion years old. billion years old. The Earth is estimated to be The Earth is estimated to be 4.5 4.5 billion billion

years old.years old.