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
GEOLOGIC TIME SCALE
EON – largest segment of geologic time
ERA- last tens to hundreds of millions of years; two or more periods.
PERIOD- last tens of millions of years and associated with rock systems.
EPOCH – smallest segment of geologic time, several million years.

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. Arranging Events in Order
Principle of uniformity
Stated that the present is the key to the past.
Look at geological features of today’s Earth as being shaped by its past.
States that the processes that are going on today to shape the Earth are the same processes that have always been going on.

6. 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.

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

8. 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

9. 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)

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

11. 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

12. 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REPLACED REMAINS – THE SOFT PARTS OF THE ORIGINAL ANIMAL HAVE DISAPPEARED AND THE HARD PARTS HAVE BEEN REPLACED BY MINERALS.

13. MOLDS AND CASTS – FOSSIL SHELLS OR BONES ARE DISSOLVED COMPLETELY 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.

14. INDEX FOSSIL - can provide the relative age of a rock layer.
-existed only during specific spans of time,
-occurred in large geographic areas, and are easily identifiable.
-i.e. trilobites

15. MEASURING ABSOLUTE TIME
TREE RINGS
EACH RING REPRESENTS A SINGLE YEAR (SPRING/FALL) THE WIDTH OF THE RING DEPENDS UPON THE TEMPERATURE AND RAINFALL

16. RADIOMETRIC DATING -uses decay of unstable isotopes.
Isotopes are atoms of an element that differ in their number of neutrons.
A half-life is the amount of time it takes for half of the isotope to decay.
Since decay rates are constant, the ratio of the decay product to the remaining amount of the original element can be used as a measure of the age of the material in which it is found.

17. 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

18. RADIOCARBON DATING USES THE RADIOACTIVE ISOTOPE CARBON-14 FOUND IN ALL LIVING THINGS. BECAUSE IT IS CONTINUALLY ABSORBED BY FOOD AND WATER, IT STAYS CONSTANT IN LIVING THINGS. WHEN THE 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
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