Absolute Age of Rocks Chapter 9 Section 3 Pgs. 257 - 261

Absolute Age Age of a rock or other object in years. Determine age by using the properties of atoms.

Parts of an Atom

Radioactive Decay The process of an unstable isotope breaking down Number of protons determines the element Number of neutrons determines the form or isotope

Beta Decay Neutron turns into a proton and electron and the electron leaves as a beta particle.

Alpha Decay Unstable parent isotope gives off 2 protons and neutrons in the form of an alpha particle

Parent Isotope Remaining (%) Half-Life Time it takes for half of the atoms isotope to decay. Number of Half-lives Parent Isotope Remaining (%) 1 100 2 X 3 25 4 12.5 5 Y

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

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

Radiocarbon Dating Carbon-14 is used to date bones, wood, and charcoal up to 75,000 years old. Living things take in carbon from environment to build their bodies. After death, carbon-14 slowly decays. Scientists compare the amount of carbon left to the environment.

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

Uniformitarianism This principle states that what’s happening on earth now also happened in the past. “The present is the key to the past.” Earth shaped by: Slow, everyday processes Violent, unusual events

Review What is radiometric age? What is radiocarbon used to date? What two types of rocks can be radiometrically dated? How old is the earth estimated to be? What is the principle of uniformatarianism? What key phrase explains this principle?