The Geologist as Detective

 THE PRINCIPLES USED IN DETERMINING THE ORDER IN WHICH ROCKS WERE FORMED

 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

 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

 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

 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

 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

 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

 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

 FOSSILS: PRESEVED 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

 Casts and Molds- shapes/outlines left behind; these are COPIES of originals.  Petrifaction- mineral replacement of organic material  Amber and Ice- organisms “frozen” in time  Trace Fossils- footprints, fecal pellets, burrows  Impressions- 2-Dimensional leftovers

 NYS HAS FOSSILS OF CORAL AND WARM- WATER MARINE ORGANISMS, INDICATING THAT THE AREA WAS ONCE A TROPICAL SEA  IT ALSO HAS MORE RECENT FOSSILS OF WOOLY MAMMOTHS AND MASTODONTS, REVEALING THE COLD, SNOWY CLIMATE OF THE LAST ICE AGE