Dating Rocks Ways to tell the age of

Dating Rocks Ways to tell the age of a rock

What are relative and absolute Locations?

2 Ways to Date Rocks: § Absolute Dating: § Gives us the true “age” of a fossil or rock § All you need is a tiny sample of material (mineral, bone) no larger than a grain of rice. § Mainly organic tissue or igneous crystals § Measures the amount of unstable isotopes that have “decayed” to figure out age

2 Ways to Date Rocks: § Relative Dating: § Places events in geologic history in the proper order relative to one another. § The basis for the geologic time scale § Does not provide a true “age”

Principles for Relative Dating: 1. Law of Superposition : • In any undisturbed sequence of strata, • the oldest layer is at the bottom • the youngest layer is at the top. Newest Oldest

Principles for Relative Dating: Law of Superposition : • In any undisturbed sequence of strata, • the oldest layer is at the bottom • the youngest layer is at the top.

Relative Dating Principles 2. The Cross-cutting Law • Any feature that cuts across a body of sediment or rock is younger than the body of sediment or rock that it cuts across.

Cross-cutting Igneous Rock Cross Cutting Relationships - Geologic features that cut through and across rocks are younger than those rocks.

Relative Dating Principles 1. Law of Superposition 2. Cross-cutting Law 3. Law of Inclusions - Rocks embedded in other rocks are older than those rocks they are embedded in.

Law of Inclusions - Rocks embedded in other rocks are older than those rocks they are embedded in. http: //www. earth. ox. ac. uk/~oesis/field/medium/xenolith-1365. jpg

Do Class 12: Relative Dating Exercise 1

Relative Dating Principles 1. Superposition Law 2. Cross-cutting Law 3. Law of Inclusions 4. Law of Original Horizontality (and Lateral continuity) – layers of sediments are originally deposited horizontally

Relative Dating Principles 4. Law of Original Horizontality (and Lateral continuity) …. But stuff can happen! • Erosion • Earthquakes • Faults • Deposition

Relative Dating Principles 4. Law of Original Horizontality (and Lateral continuity) …. But stuff can happen! • Erosion • Earthquakes • Faults • Deposition

Relative Dating Principles 4. Law of Original Horizontality (and Lateral continuity) …. But stuff can happen! • Erosion • Earthquakes • Faults • Deposition

Types of Discomformities • Angular conformity: younger sediments rest upon the eroded surface of tilted or folded older rocks. • Disconformity: contact between younger and older beds is marked by a visible, irregular or uneven erosional surface. • Paraconformity: beds above and below the unconformity are parallel and no erosional surface is evident; but can be recognized based on the gap in the rock record. • Nonconformity: develops between sedimentary rock and older igneous or metamorphic rock that has been exposed to erosion.

A DISCONFORMITY is a boundary between two layers of non-continuous ages. This boundary is usually marked by an erosional surface and is often irregular. 5. M&W 4 Fig. 17. 8; M&W 5 Fig. 17. 8

An ANGULAR UNCONFORMITY is a disconformity between layers of different angles. The underlying layers are first tilted, then erosion scours away a new, horizontal surface. New, horizontal layers form on top

An NONCONFORMITY is a disconformity between different rock types, one of them sedimentary.

Activity 3: Relative Dating Exercise A The Oldest T The Youngest

Activity 2: Label the layers from: A The Oldest T The Youngest KEY