1. Geologic Time Scale Day 2
Fill in the blanks of the note sheet as you view the presentation
Interpreting Rock Strata Practice

2. READING THE ROCK RECORD
RELATIVE TIME VS ABSOLUTE TIME
PLACES EVENTS IN A SEQUENCE BUT DOES NOT IDENTIFY THEIR ACTUAL DATE OF OCCURRENCE
IDENTIFIES THE ACTUAL DATES OF GEOLOGIC EVENTS
EXAMPLE
A LIST IN CHRONOLOGICAL ORDER OF WHAT YOU HAVE DONE TODAY UP UNTIL THIS TIME
THE EXACT TIMES AT WHICH YOU DID THESE THINGS

3. FINDING THE AGE OF ROCKS
WITH RELATIVE TIME
LAW OF SUPERPOSITION- IN UNDISTURBED SEDIMENTARY ROCKS THE OLDEST ROCK LAYERS ARE AT THE BOTTOM AND THE YOUNGEST ARE AT THE TOP.
OLDER
YOUNGER

4. LAW OF CROSS-CUTTING RELATIONSHIPS- AN IGNEOUS INTRUSION IS YOUNGER THAN THE ROCK IT HAS INTRUDED INTO. (LOOK AT THE WHISKERS!)
INTRUSION

5. LAW OF INCLUDED FRAGMENTS - IF FRAGMENTS OF ONE TYPE OF ROCK ARE FOUND IN ANOTHER ROCK LAYER THE ROCK FRAGMENTS MUST BE OLDER THAN THE ROCK LAYER IN WHICH THEY ARE FOUND
FAULTED AND FOLDED LAYERS - LAYERS OF ROCK THAT HAVE BEEN FAULTED OR FOLDED MUST HAVE BEEN PRESENT BEFORE THE ACTIONS OF FAULTING OR FOLDING TOOK PLACE
FOLDING
FAULTING

6. UNCONFORMITY- A PLACE IN THE ROCK RECORD WHERE LAYERS OF ROCK ARE MISSING BECAUSE OF UPLIFT AND EROSION. THE RESULT CAN BE A LARGE AGE DIFFERENCE BETWEEN THE ROCKS ABOVE AND THOSE BELOW THE EROSIONAL SURFACE (IT APPEARS LIKE A SQUIGGLY LINE IN A CROSS-SECTION)

7. ROCK CORRELATION
MATCHING OF ROCK LAYERS THAT CAN BE SEEN AT THE EARTH’S SURFACE, OVER A LARGE AREA
AN OUTCROP IS EXPOSED ROCK LAYERS AT THE EARTH’S SURFACE
A KEY BED IS A THIN, WIDESPREAD LAYER, USUALLY OF VOLCANIC ASH, THAT CAN BE USED TO CORRELATE AN EXACT POINT OF TIME

8. FOSSILS A FOSSIL IS ANY EVIDENCE OF EARLIER LIFE PRESERVED IN THE ROCK
ORIGINAL REMAINS (RARE) – THE ACTUAL UNCHANGED REMAINS OF THE PLANT OR ANIMAL ARE PRESERVED.
REPLACED REMAINS – THE SOFT PARTS OF THE ORIGINAL ANIMAL HAVE DISAPPEARED AND THE HARD PARTS HAVE BEEN REPLACED BY MINERAL MATERIAL. (PETRIFIED WOOD)

9. MOLDS AND CASTS – FOSSIL SHELLS OR BONES ARE DISSOLVED COMPLETELY OUT OF THE ROCK LEAVING A HOLLOW DEPRESSION IN THE ROCK. NEW MINERAL MATERIAL FILLS THE MOLD IT FORMS A CAST OF THE ORIGINAL FOSSIL.
TRACE FOSSILS – EVIDENCE OF LIFE OTHER THEN REMAINS, WHICH INCLUDES ANY IMPRESSIONS LEFT IN THE ROCK. (TRAILS, FOOTPRINTS, TRACKS, BURROWS)

10. INDEX FOSSIL EASILY IDENTIFIABLE LIVED IN A SHORT TIME RANGE
EASILY IDENTIFIABLE
LIVED IN A SHORT TIME RANGE
WIDESPREAD OCCURRENCE

11. Rock Strata Practice
Complete the top section using your class notes and then use the key to answer the questions about rock strata