Introduction

Question 1

Geologic timescale (eons)

Answer 1

1. Hadean (4.6 Ga-4 Ga)
2. Archean (4 Ga-2.5 Ga) - early forms of life
3. Proterozoic (2.5 Ga-541 Ma)
4. Phanerozoic: (541 Ma-)

Question 2

Stratigraphy

Answer 2

Study of rock layers

• Mostly sedimentary rocks
• Law of superposition

Question 3

Lithostratigraphy

Answer 3

Looking at physical characteristics of rock itself (no fossils)

• Age correlation based on rock units themselves
• Form of relative dating (won’t tell you absolute ages of rocks with this method alone)
• Best for local-to-regional scales

Question 4

Biostratigraphy

Answer 4

Based on fossil occurrences; wherever you find a specific organism, you know you’re in some specific band of time (assumption that these organisms were prolific during a specific time) → constructs geologic time scale

• Form of relative dating
• Most common form of dating in earth history
• Best candidates are index fossils
• Ideally widespread (found “everywhere”) but for a brief time period (common in conodont species)

Question 5

Magnetostratigraphy

Answer 5

Based on Earth’s magnetic polarity; if you know where you are in polarity sequence, you know relative ages

• Form of relative dating
• Zipper with bands of similar age rocks/minerals that record the same polarity

Question 6

Chronostratigraphy

Answer 6

Radioactive decay

• Only form of absolute dating