GEOLOGIC TIME

• Concepts of Time

1. absolute age: # of years since the rock formed

2. relative age: age of sedimentary rock layers in relation to on another

• Relative Dating Techniques

1. Stratigraphic Record

i. principle of original horizontality

ii. principle of superposition

• Relative Dating Techniques

1. Stratigraphic Record

iii. unconformities

(1) disconformity: erosion removes a part of otherwise undisturbed rock

(2) angular unconformity: rocks below are at an angle in relation to those above

(3) nonconformity: sedimentary rocks lie on top of igneous rocks

• Relative Dating Techniques

1. Stratigraphic Record

iv. principle of cross-cutting relationships

Fossils (paleontology)

i. faunal succession

(1) formations

Absolute Time Scale

1. Four major time units

i. eons

ii. eras

iii. periods

iv. epochs

2. Determining absolute time

i. radiometric dating

(1) radioactivity

2. Determining absolute time

i. radiometric dating

(2) half-life

(3) types

Major assumptions

• Decay rate is constant and accurately known.

• Rock or mineral has remained a “closed” system.

• Daughter is solely a product of the radioactive decay of the parent.

Geologic Time Scale

•IMPACT: The earth had not been created through a series of catastrophes, but had instead evolved through the same types of change that can be observed today

1. THE PRESENT IS THE KEY TO THE PAST!

•Earth and the neighboring planets formed on January 1

•Jan. and Feb. Earth differentiated a core, mantle, and crust

•Feb. 21, life evolved

•Spring, summer, and fall continents and oceans differentiated and plate tectonics started

•multicelled organisms appeared on October 25

•in late November plants and animals became abundant on land

•on December 15 the dinosaurs appeared

•by December 25 they became extinct

•we arrived on December 31 at 11:20 p.m.

•and less than a second and a half before midnight on that same day the Industrial Revolution began