Earth’s History is Earth’s History is Recorded in RocksRecorded in Rocks

Two Methods to Date Rocks.Two Methods to Date Rocks.

Relative AgeRelative Age How old your relatives How old your relatives

are.are. Age of an object Age of an object

compared with the compared with the ages of other objects.ages of other objects.– The blackboard is older The blackboard is older

than the chalk on it.than the chalk on it. How do you determine How do you determine

relative age?relative age?– Relative DatingRelative Dating

Dating in the South.Dating in the South.

Absolute AgeAbsolute Age

Actual age of an object.Actual age of an object.

Methods of EstimatingMethods of EstimatingAbsolute AgeAbsolute Age

1.1. Rates of DepositionRates of Deposition

2.2. Rates of ErosionRates of Erosion

3.3. Using ChemistryUsing Chemistry

Radioactive DecayRadioactive Decay

Atoms that are unstable (too much Atoms that are unstable (too much energy) decay (lose energy) at a energy) decay (lose energy) at a constant rate into other, more stable, constant rate into other, more stable, substances.substances.

Radioactive Decay ContinuedRadioactive Decay Continued

Lose protons to become more stable.Lose protons to become more stable. Happens in the nucleus.Happens in the nucleus. Unstable elements (parent isotope) Unstable elements (parent isotope)

change into more stable isotope change into more stable isotope (daughter isotope).(daughter isotope).– Isotope – Elements with the same Isotope – Elements with the same

number of protons, but a different number of protons, but a different number of neutrons.number of neutrons.Example – C-12 & C-14 (2 more neutrons)Example – C-12 & C-14 (2 more neutrons)

Half LifeHalf Life

The time required for half the mass The time required for half the mass of a radioactive element to decay of a radioactive element to decay into its daughter elements.into its daughter elements.

Decay rate is always Decay rate is always constantconstant..

Carbon Carbon DatingDating

Carbon DatingCarbon Dating– Uses the isotope C-14 (parent element).Uses the isotope C-14 (parent element).

– Living things ingest C-14 in the COLiving things ingest C-14 in the CO22 in in the atmosphere. Whey they die they the atmosphere. Whey they die they don’t and it decays to form the daughter don’t and it decays to form the daughter element N-14.element N-14.

– ½ life of C-14 is 5,730 years.½ life of C-14 is 5,730 years.– Only used for organic materials.Only used for organic materials.– Only good up to about 50,000 years.Only good up to about 50,000 years.