Absolute Age of Absolute Age of RocksRocks

Chapter 9 Section Chapter 9 Section 33

Pgs. 257 - 261Pgs. 257 - 261

Absolute AgeAbsolute Age

• Age of a rock or other Age of a rock or other object in years.object in years.

• Determine age by using Determine age by using the properties of atoms.the properties of atoms.

Parts of an AtomParts of an Atom

Radioactive Radioactive DecayDecay

• The process of an unstable The process of an unstable isotope breaking downisotope breaking down• Number of protons Number of protons determines the elementdetermines the element• Number of neutrons Number of neutrons determines the form or determines the form or isotopeisotope

Beta DecayBeta Decay• Neutron turns into a Neutron turns into a

proton and electron and proton and electron and the electron leaves as a the electron leaves as a beta particle.beta particle.

Alpha DecayAlpha Decay• Unstable parent isotope gives off Unstable parent isotope gives off

2 protons and neutrons in the 2 protons and neutrons in the form of an alpha particleform of an alpha particle

Half-LifeHalf-Life• Time it takes for half of Time it takes for half of the atoms isotope to the atoms isotope to decay.decay.Number of Half-

livesParent Isotope Remaining

(%)

1 100

2 X

3 25

4 12.5

5 Y

ReviewReview• What is absolute age?What is absolute age?• Draw an atom and label its Draw an atom and label its parts.parts.• What is radioactive decay?What is radioactive decay?• What is beta decay? Alpha What is beta decay? Alpha decay?decay?• What is a half-life?What is a half-life?

Radiometric Radiometric AgesAges

• Measure the ratio of Measure the ratio of parent isotope to parent isotope to daughter product, can daughter product, can find the absolute age of find the absolute age of a rock.a rock.

Radiocarbon Radiocarbon DatingDating• Carbon-14 is used to date bones, Carbon-14 is used to date bones,

wood, and charcoal up to 75,000 wood, and charcoal up to 75,000 years old.years old.

• Living things take in carbon from Living things take in carbon from environment to build their environment to build their bodies.bodies.

• After death, carbon-14 slowly After death, carbon-14 slowly decays.decays.

• Scientists compare the amount of Scientists compare the amount of carbon left to the environment.carbon left to the environment.

Rock AgesRock Ages• Only igneous and Only igneous and metamorphic rocks can be metamorphic rocks can be radiometrically dated.radiometrically dated.• Oldest rocks found are Oldest rocks found are 3.96 billion years old.3.96 billion years old.• Estimate earth to be about Estimate earth to be about 4.5 billion years old.4.5 billion years old.

UniformitarianisUniformitarianismm• This principle states that This principle states that

what’s happening on earth what’s happening on earth now also happened in the now also happened in the past.past.• ““The present is the key to the The present is the key to the

past.”past.”• Earth shaped by:Earth shaped by:–Slow, everyday processesSlow, everyday processes–Violent, unusual eventsViolent, unusual events

ReviewReview• What is radiometric age?What is radiometric age?• What is radiocarbon used to date?What is radiocarbon used to date?• What two types of rocks can be What two types of rocks can be

radiometrically dated?radiometrically dated?• How old is the earth estimated to How old is the earth estimated to

be? be? • What is the principle of What is the principle of

uniformatarianism?uniformatarianism?• What key phrase explains this What key phrase explains this

principle?principle?