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Interpreting Earth’s History

Interpreting Earth’s History. The Geologist as Detective. READING THE ROCK RECORD. THE PRINCIPLES USED IN DETERMINING THE ORDER IN WHICH ROCKS WERE FORMED. Uniformitarianism.

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Interpreting Earth’s History

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  1. Interpreting Earth’s History The Geologist as Detective

  2. READING THE ROCK RECORD • THE PRINCIPLES USED IN DETERMINING THE ORDER IN WHICH ROCKS WERE FORMED

  3. Uniformitarianism • The idea that processes that shape the Earth, such as volcanoes, earthquakes, deposition and erosion, are the same processes that occurred in the geologic past

  4. Principle of Horizontality • THE PRINCIPLE IS BASED ON THE FACT THAT SEDIMENT IS USUALLY DEPOSITED IN HORIZONTAL LAYERS • IF SEDIMENTARY ROCKS LIE AT AN ANGLE THEN SOME TECTONIC FORCES MUST HAVE ACTED ON THE ROCK

  5. Law of Superposition • THAT SEDIMENTARY ROCKS ARE OLDEST ON THE BOTTOM AND YOUNGEST ON TOP • THIS IS TRUE AS LONG AS NO TECTONIC FORCES HAVE TURNED THE LAYERS UPSIDE DOWN OR ON THEIR SIDE

  6. THE PRINCIPLE OF CROSS CUTTING RELATIONSHIPS • ROCK MUST FIRST EXIST BEFORE ANYTHING CAN HAPPEN TO IT • THEREFORE AN INTRUSION IS YOUNGER THAN THE ROCK IT HAS ENTERED • INTRUSION: WHEN MAGMA SQUEEZES INTO OR BETWEEN LAYERS OF PRE-EXISTING ROCK • EXTRUSION: WHEN MOLTEN ROCK FLOWS ONTO THE EARTH’S SURFACE, THEN COOLS • INCLUSION: OLDER ROCKS SURROUNDED BY MOLTEN MAGMA

  7. THE LAW OF INCLUDED FRAGMENTS • ONE PIECE OF ROCK FOUND IN ANOTHER ROCK MUST BE OLDER THAN THE ROCK IT IS FOUND IN • A PEBBLE FOUND IN CONGLOMERATE IS OLDER THAN THE CONGLOMERATE ITSELF

  8. AN UNCONFORMITY IN THE ROCK RECORD • WHERE LAYERS OF ROCK ARE MISSING • IF THE SURFACE OF THE ROCK WAS ERODED SOME TIME IN ITS HISTORY • UNCONFORMITIES ARE GAPS IN GEOLOGICAL TIME

  9. FOLDS AND FAULTS • FOLDS: BENDS IN ROCK LAYERS PRODUCED BY CRUSTAL PLATE MOVEMENTS • FAULTS: BREAKS IN ROCK WHERE MOVEMENT HAS OCCURRED • FOLDING OR FAULTING CAN LEAD TO EXCEPTIONS TO THE LAW OF SUPERPOSITION

  10. FOSSILS • FOSSILS: PRESERVED REMAINS OR TRACES OF LIVING THINGS • RELATIVE AGE: COMPARATIVE AGE; AGE EXPRESSED AS BEFORE OR AFTER OTHER EVENTS WITHOUT SPECIFYING THE AGE IN UNITS • ABSOLUTE AGE:AGE OF A ROCK UNIT, FOSSIL OR EVENT EXPRESSED IN UNITS OF TIME, SUCH AS YEARS

  11. TYPES OF FOSSILS • Casts and Molds- shapes/outlines left behind; these are COPIES of originals (3D) • Petrifaction- mineral replacement of organic material • Amber and Ice- organisms “frozen” in time • Trace Fossils- footprints, fecal pellets, burrows • Impressions- 2-Dimensional leftovers (like a stamp)

  12. CAST AND MOLDS

  13. PETRIFICATION

  14. AMBER AND ICE

  15. TRACE FOSSILS

  16. IMPRESSIONS

  17. THIS ONE’S JUST CRAZY!

  18. NYS FUN FACTS • NYS HAS FOSSILS OF CORAL AND WARM-WATER MARINE ORGANISMS, INDICATING THAT THE AREA WAS ONCE A TROPICAL SEA • RECENT FOSSILS OF WOOLY MAMMOTHS AND MASTODONTS, REVEAL THE COLD, SNOWY CLIMATE OF THE LAST ICE AGE

  19. Video • https://www.youtube.com/watch?v=M2Ex5DIjtfU • Video won’t load? Search for: Laws of Relative dating by London Jenks • Bullet-point suggestion: analogies for the laws (ie footprints for superposition)

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