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  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”  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.

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.conformity Disconformity: contact between younger and older beds is marked by a visible, irregular or uneven erosional surface.conformitybeds 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.conformitybeds unconformity Nonconformity: develops between sedimentary rock and older igneous or metamorphic rock that has been exposed to erosion.conformity

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&W4 Fig. 17.8; M&W5 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