Monday

• Time Scales–Human time frames versus

geological time frames

–Various time scales• Human, biological, geological & astronomical

Time frames and amount of impact relating to various geologic phenomena

HDF – 1995 and HUDF 2003-2004

• Relative age–Youngest or oldest

• Absolute age–Age in number of years

(Numerical)

Measuring Time

Relative Age• Law of Superposition:

younger on older• Law of cross-cutting

relationships• Law of Original Horizontality• Law of Faunal Succession

Superposition

Cross-cutting Relationships

Putting it together

Hutton’s Unconformity

Faunal Succession

Geologic Time scale Eras• Cenozoic - “recent life”

– age of Mammals <66 mya

• Mesozoic - “middle life”– age of Dinosaurs 245-66 mya

• Paleozoic - “ancient life”– Age of Trilobites 570-245 mya

• Precambrian – Proterzoic & Archean

Cenozoic

Mesozoic

Paleozoic

Precambrian

Feathered dinosaurs

Coelacanth; ‘fossil’ fish

Trilobite

PrecambrianFossil deposits

Absolute Age

• Involves ‘decay’ of atoms

• A constant process that occurs with atoms

A process involving the nucleus

A loss of 2 protons & 2 neutrons

Converting a neutron to a proton

Absolute Age

• Clock starts when Parent atoms are “trapped” in rock at time of crystallization.

• Therefore must be Igneous rock.• Volcanic rocks cool quickly thus are best. • With time Daughter atoms form and are

trapped. • We count number of Parent atoms and

Daughter atoms.

Age of Earth• Oldest ocean crust 3.8 x 109 or 3.8 billion

years old (Greenland)– Indicates plate tectonics at work

• Oldest Rocks: 4.28 x 109 years or 4.28 billion years old (Canada)– Indicates stable crust exists

• Oldest Mineral: 4.4 x 109 years or 4.4 billion years old (Australia)– Indicates oldest date of rocks

• Meteorites (and Earth) 4.56 x 109 years or 4.56 billion years