Presentation on theme: "Ways to tell the age of a rock"— Presentation transcript:
1Ways to tell the age of a rock Dating RocksWays to tell the age of a rock
22 Ways to Date Rocks: Relative Dating: Places events in geologic history in the proper order.The basis for the geologic time scaleMainly Sedimentary RocksDoes not provide a true “age”
32 Ways to Date Rocks: Absolute Dating: All you need is a tiny sample of material (mineral, bone) no larger than a grain of rice.Gives us the true “age” of a fossil or rockMainly organic tissue or igneous crystalsMeasure the amount of unstable isotopes that have “decayed” to figure out age
4Principles for Relative Dating: Superposition - The youngest rocks are on the top, oldest at the bottom.
13Relative Dating Principles SuperpositionCross-cutting relationshipsLaw of InclusionsLaw of Original Horizontality (and Lateral continuity)Law of Unconformities
14A DISCONFORMITY is a boundary between two layers of non-continuous ages. This boundary is usually markedby an erosionalsurface and isoften irregular.M&W4 Fig. 17.8; M&W5 Fig. 17.8
15An 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
16An NONCONFORMITY is a disconformity between different rock types, one of them sedimentary.
17Activity 2: Label the layers from: A The OldestT The Youngest
18Activity 2: Label the layers from: A The OldestT The Youngest