NOTES - Radiometric Dating.doc

III) Dating Rocks of the Earth --- Radiometric Dating

A) Radiometric Dating – Determining numerical dates (ages) of rocks by calculating the rates of decay of radioactive elements in the rocks.

1) Radioactive Elements – Elements that release energy when their nuclei break down.

++ Examples: Parent Atom Uranium 238 decays to Daughter Atom Lead 206, Parent Atom Thorium 232 decays to Daughter Atom Lead 208.

2) Radioactive Decay – The nucleus of a radioactive element breaks down.

++ When the nucleus decays it loses neutrons and protons.

++ Decaying creates a stable atom know as a Daughter Atom.

++ The original atom is called the Parent Atom.

3) Igneous rocks naturally have radioactive elements in them like U 238 and Th 232.

B) Radiometric Dating techniques rely on measuring the half-life of radioactive elements.

1) Half-life – Length of time it takes for one-half of the atoms in a radioactive element to decay.

++ Parent Atom = the radioactive element’s atoms ++ Daughter Atom = stable element’s atoms

++ Parent Atoms decay to Daughter Atoms so ….. Parent Atoms + Daughter Atom = 100%

2) In radiometric dating scientists find the ratio of Parent Atoms to Daughter Atoms.

++ Using this ratio and the known half-life of the radioactive element, the age of a rock can be determined.

3) Half-life Math Chart:

Number of Half-lives % of Original

Parent atoms

0

1

2 3 4

5

 C) Carbon Dating – Using the decay of Carbon 14 in once

living organisms to find numerical ages.

++ All living organisms have Carbon 14 w/ a half-life of 5730 years.

++ Carbon 14 decays to Nitrogen 14.

III) Dating Rocks of the Earth

---Radiometric Dating

A) Radiometric Dating –

Determining

numerical

dates (ages)

of rocks

A) Radiometric Dating – Determining numerical dates (ages) of rocks by calculating the rates of decay of radioactive elements in the rocks.

1)

Radioactive Elements

– Elements that

release energy

when

their

nuclei break



A) Radiometric Dating – Determining numerical dates (ages) of rocks by calculating the rates of decay of radioactive elements in the rocks.

1) Radioactive Elements – Elements that release energy when their nuclei break down.

++ Examples:

i) Parent Atom

Uranium

238

decays to Daughter

Atom

Lead 206

ii)

Parent Atom Thorium

232

decays to

Daughter

 ++ Examples:

i) Parent Atom Uranium 238 decays to Daughter Atom Lead 206.

ii) Parent Atom Thorium 232 decays to Daughter Atom Lead 208.

2) Radioactive Decay –

The nucleus of a

radioactive element

2) Radioactive Decay – The nucleus of a radioactive element breaks down.

++ When the nucleus

decays it loses

neutrons

and

++ When the nucleus decays it loses neutrons and protons.

++ Decaying creates a

stable atom

know as a

++ Decaying creates a stable atom know as a Daughter Atom.

++ The original atom is

called the

Parent



++ Decaying creates a stable atom know as a Daughter Atom.

++ The original atom is called the Parent Atom.

3) Igneous rocks

naturally have

3) Igneous rocks naturally have radioactive elements in them like U 238 and Th 232.

B)

Radiometric Dating

B) Radiometric Dating techniques rely on measuring the half-life of radioactive elements.

1) Half-life – Length of time it takes for one-half of the atoms in a radioactive element to decay.

++

Parent Atom

= the

radioactive element’s

atoms

++

Daughter Atom

=

stable element’s

++ Parent Atom = the radioactive element’s atoms ++ Daughter Atom = stable element’s atoms

++

Parent Atoms

decay

to

Daughter Atoms

so

…..

Parent Atoms +

Daughter Atom =

++ Parent Atoms decay to Daughter Atoms so ….. Parent Atoms + Daughter Atom = 100%

2) In radiometric

dating scientists find

the

ratio of Parent

2) In radiometric dating scientists find the ratio of Parent Atoms to Daughter Atoms.

++ Using this

ratio

and

the known

half-life

of

the

radioactive

element

, the age of a

rock can be

++ Using this ratio and the known half-life of the radioactive element, the age of a rock can be determined.

3) Half-life Math Chart:

Number of Half-lives % of Original

Parent atoms Age of Radioactive

 _{Number of}

Half-lives % of Original

Parent atoms

0

1

2 3 4

5

Number of Half-lives % of Original

Parent atoms

0

1

2 3 4

5

100 50 25 12.5 6.25 3.125



Half life math Example 1:

Element P is a radioactive parent and

decays to daughter

Element B

.

Element P has a half-life of

3 million

years

(m.y.).

Element P is in a

rock sample

.

Question 1: Age of rock after 2

half-lives of Element P?

Question 2: Number of half-lives of P

if 6.25% of P remains?

Question 3: Amount of P remaining

after 2 half-lives? Amount B

remaining?

Half-lives % of Original

Parent atoms

0

1

2 3 4

5

100 50 25 12.5 6.25 3.125

Age of Radioactive

Half life math Example 2:

Element Qq is a radioactive parent

and decays to daughter

Element Ki

.

Element Qq has a half-life of

5,000

years

Question 1: How many half-lives of

Element Qq if rock is 12,200 years

old?

Question 2: Age of rock if 3.3

half-lives of Qq have passed?

Question 3: Ratio of Qq to Ki if 38%

of original Qq is present? Qq= Ki=

Number of Half-lives % of Original

Parent atoms

0

1

2 3 4

5

100 50 25 12.5 6.25 3.125

Age of Radioactive

C) Carbon Dating –

Using the decay of

Carbon 14

in

once

C) Carbon Dating – Using the decay of Carbon 14 in once living organisms to find numerical ages.

++ All

living

organisms

have

++ All living organisms have Carbon 14 w/ a half-life of 5730 years.

++ Carbon 14 decays to Nitrogen 14.