1. Earth History

2. IT IS ESTIMATED THAT THE EARTH FORMED ALONG WITH THE SOLAR SYSTEM 4
IT IS ESTIMATED THAT THE EARTH FORMED ALONG WITH THE SOLAR SYSTEM 4.6 BILLION YEARS AGO (4,600 MYA)
GEOLOGIC TIME SCALE
A SUMMARY OF THE MAJOR EVENTS IN EARTH’S HISTORY
EON – largest segment of geologic time
ERA
PERIOD
EPOCH – smallest segment of geologic time

4. 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

5. 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.

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

7. 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

8. 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)

9. PLACE THE FOLLOWING EVENTS IN ORDER STARTING WITH THE OLDEST.B I G K M F C A D H J

10. 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

11. 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REPLACED REMAINS – THE SOFT PARTS OF THE ORIGINAL ANIMAL HAVE DISAPPEARED AND THE HARD PARTS HAVE BEEN REPLACED BY MINERAL MATERIAL.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)

12. 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)

13. INDEX FOSSIL
EASILY IDENTIFIABLE
SHORT-LIVED
WIDESPREAD OCCURRENCE

14. MEASURING ABSOLUTE TIME
TREE RINGS
EACH RING REPRESENTS A SINGLE YEAR (SPRING/FALL) THE WIDTH OF THE RING DEPENDS UPON THE TEMPERATURE AND RAINFALL
VARVES
GLACIAL LAKE DEPOSITS. A THICK LIGHT COLORED LAYER IN THE SUMMER AND A THIN DARK LAYER IN THE WINTER

15. RADIOACTIVE DATING
USED TO DATE FAR BACK IN TIME. CERTAIN ROCKS CONTAIN RADIOACTIVE ISOTOPES
RADIOACTIVE ISOTOPES ARE ATOMS OF ELEMENTS THAT GIVE OFF RADIATION FROM THEIR NUCLEI
RADIOACTIVE DECAY IS THE PROCESS BY WHICH A RADIOACTIVE ISOTOPE CHANGES INTO A NEW STABLE ELEMENT

16. HALF-LIFE
THE RATE AT WHICH A RADIOACTIVE ELEMENT DECAYS. IT IS THE TIME IT TAKES FOR HALF OF THE ATOMS OF THE RADIOACTIVE ELEMENT TO DECAY TO A STABLE END PRODUCT (SEE PAGE 1 OF THE ESRT)
AT THE END OF EACH HALF-LIFE, HALF OF THE RADIOACTIVE MATERIAL REMAINS
PARENT ISOTOPE = THE RADIOACTIVE ISOTOPE THAT BEGINS
DAUGHTER ISOTOPE = THE STABLE ISOTOPE THAT HAS BEEN CHANGED

17. RADIOCARBON DATING USES THE RADIOACTIVE ISOTOPE CARBON-14 FOUND IN ALL LIVING THINGS. BECAUSE CARBON-14 IS CONTINUALLY ABSORBED BY FOOD AND WATER IT STAYS CONSTANT IN LIVING THINGS. WHEN THE LIVING THING DIES THE PERCENTAGE OF CARBON-14 DECREASES AT THE RATE OF ITS HALF-LIFE. CAN BE USED TO DATE BACK ABOUT 100,000 YEARS

18. URANIUM LEAD METHOD IS USEFUL TO DATE ROCKS OLDER THAN 10 MILLION YEARS. CAN BE USED ONLY ON IGNEOUS ROCKS THAT CONTAIN THE RIGHT KIND OF URANIUM
RUBIDIUM-STRONTIUM METHOD CAN ALSO BE USED TO DATE OLDER ROCKS BECAUSE OF ITS LONG HALF-LIFE. IT IS ALSO VERY COMMONLY FOUND IN IGNEOUS ROCKS.
POTASSIUM-ARGON METHOD IS VERY USEFUL SINCE POTASSIUM-40 CAN BE FOUND IN METAMORPHIC, SEDIMENTARY, AND IGNEOUS ROCKS. IT CAN DATE OLDER ROCKS BUT MAY ALSO DATE ROCKS AS YOUNG AS 50,000 YEARS