GEOLOGIC TIME

Earth’s History Compressed:

GEOLOGIC TIME

I. Early Efforts of Dating the Age of the Earth

GEOLOGIC TIME

I. Early Efforts of Dating the Age of the Earth

A. James Ussher (mid 1600's)

4004 B.C.

I. Early Efforts of Dating the Age of the Earth

B. Georges Buffon (mid 1700's)

C. Lord Kelvin (late 1800's)

75,000 yr

20-40 m.y.

I. Early Efforts of Dating the Age of the Earth

D. Charles Walcott (1893)

75 m.y.

I. Early Efforts of Dating the Age of the Earth

E. John Joly (1899)

90 m.y.

II. Constancy of Natural Laws

II. Constancy of Natural Laws

A. Catastrophism

• Georges Cuvier (late 1700's)

A. Catastrophism

• Georges Cuvier (late 1700's)

B. Uniformitarianism

• James Hutton (late 1700's)

III. Types of Geologic Dating

A. Relative Dating

B. Radiometric Dating

III. Types of Geologic Dating

A. Relative Dating

1. Law of Superposition

III. Types of Geologic Dating

A. Relative Dating

1. Law of Superposition

2. Law of Original Horizontality

III. Types of Geologic Dating

A. Relative Dating

1. Law of Superposition

2. Law of Original Horizontality

3. Law of Cross Cutting Relationships

III. Types of Geologic Dating

A. Relative Dating

1. Law of Superposition

2. Law of Original Horizontality

3. Law of Cross Cutting Relationships

4. Law of Faunal Succession

III. Types of Geologic Dating

A. Relative Dating

1. Law of Superposition

2. Law of Original Horizontality

3. Law of Cross Cutting Relationships

4. Law of Faunal Succession

5. Unconformities

III. Types of Geologic Dating

5. Unconformities– Disconformity– Angular Unconformity– Non Conformity

An Example……

III. Types of Geologic Dating

B. Radiometric Dating

1. Types of decay

III. Types of Geologic Dating

• alpha decay

III. Types of Geologic Dating

• alpha decay

III. Types of Geologic Dating

• beta decay

III. Types of Geologic Dating

• beta decay

III. Types of Geologic Dating

electron capture

III. Types of Geologic Dating

electron capture

III. Types of Geologic Dating

neutron capture

NP

III. Types of Geologic Dating

B. Radiometric Dating

1. Types of decay

• alpha decay

• beta decay

• electron capture

• neutron capture

An Example….

Parent

U238

An Example….

Parent

U238

92 protons

146 neutrons

An Example….

Parent

U238 → 8 alpha + 6 beta = ?92 protons

146 neutrons

An Example….

Parent

U238 → 8 alpha + 6 beta92 protons 8 {lose 2 protons} +

8{lose 2 neutrons}

An Example….

Parent

U238 → 8 alpha + 6 beta 8 {lose 2 protons} +

8 {lose 2 neutrons}

- 16 protons

- 16 neutrons

An Example….

Parent

U238 → 8 alpha + 6 beta 8 {lose 2 protons} +

8 {lose 2 neutrons}

- 16 protons

- 16 neutrons

An Example….

ParentU238 → 8 alpha + 6 beta

8 {lose 2 protons} + 6 (add 1 proton)

8 {lose 2 neutrons}

- 16 protons - 16 neutrons

An Example….

Parent

U238 → 8 alpha + 6 beta 8 {lose 2 protons} + 6 (add 1 proton)

{lose 2 neutrons}

- 16 protons + 6 protons

- 16 neutrons

An Example….

ParentU238 → 8 alpha + 6 beta

8 {lose 2 protons} + 6 (add 1 proton)

{lose 2 neutrons}

- 16 protons + 6 protons = - 10 protons- 16 neutrons

- 10 atomic number

An Example….

ParentU238 → 8 alpha + 6 beta

8 {lose 2 protons} + 6 (add 1 proton)

{lose 2 neutrons}

- 16 protons + 6 protons = - 10 protons- 16 neutrons- 32 atomic mass - 10 atomic

number

An Example….

ParentU238 → 8 alpha + 6 beta

8 {lose 2 protons} + 6 (add 1 proton)

{lose 2 neutrons}

- 16 protons + 6 protons = - 10 protons- 16 neutrons- 32 atomic mass - 10 atomic

number

U238 – 32 = “X” 206

An Example….

ParentU238 → 8 alpha + 6 beta

8 {lose 2 protons} + 6 (add 1 proton)

{lose 2 neutrons}

- 16 protons + 6 protons = - 10 protons- 16 neutrons- 32 atomic mass - 10 atomic

number

U238 – 32 = “X” 206

92 protons – 10 protons = 82 protons

An Example….

ParentU238 → 8 alpha + 6 beta

8 {lose 2 protons} + 6 (add 1 proton)

{lose 2 neutrons}

- 16 protons + 6 protons = - 10 protons- 16 neutrons- 32 atomic mass - 10 atomic

number

U238 – 32 = “X” 206

92 protons – 10 protons = 82 protons

“X” 206 with 82 protons

U238 – 32 = “X” 206

92 protons – 10 protons = 82 protons

An Example….

Parent

U238 → 8 alpha + 6 beta = ?

Pb206

Atomic # = 82

III. Types of Geologic Dating

B. Radiometric Dating

2. Half lifes, Parents, and Daughters

III. Types of Geologic Dating

B. Radiometric Dating2. Half lifes, Parents, and Daughters

half life (def)n : the time required for something to fall to

half its initial value (in particular, the time for half the atoms in a radioactive substance to disintegrate)

C14 → N14 5730 years organic carbon

III. Types of Geologic Dating

B. Radiometric Dating

3. An example

B. Carbon Dating

IV. Geologic Time