Concept Review – Geologic Time. Geologists are now able to assign fairly accurate dates to events in Earth history. There are two main types of geologic time: relative time and absolute time .
Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author.While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server.
- Relative dating means that dates are placed in their proper sequence or order without knowing their specific age in years (like knowing your mom is older than you without knowing her age).
- Absolute dating is when you can attribute a specific time to an event or specimen (like knowing the exact date you were born helps us know how old you are).
- Principle of Original Horizontality: Layers of sediment are generally deposited in a horizontal position, then moved or upturned.
- Principle of Fossil Succession: Fossil organisms succeed one another in a definite and predictable order, so any time period can be recognized by its fossil content.
Something happened here! But what??
An unconformity is a surface that represents a break in the geologic record. The rock unit(s) immediately above the break is/are much younger than that/those below. Usually represent buried erosional surfaces – parcel of geology is missing!
1) Disconformity: unconformity is parallel to layering, but there is a gap in the geologic record. (Typically erosional and hard to spot.) Look for weathering surfaces, boulders/pebbles of older rock in younger.
2) Angular Unconformity: Younger strata overly older rocks that were tilted/folded.
3) Nonconformity: A contact in which an erosional surface on a plutonic or metamorphic rock has been covered by younger sediments or volcanic rocks (i.e., unconformity separates different rock types).