GEOLOGIC TIME

PRECAMBRIAN TIME  4.6 B.Y.A. – 600 M.Y.A.  88 PERCENT OF EARTH’S HISTORY  FOSSILS ARE RARE! WHY? FOSSILS WHERE SOFT BODIED, LACKED BONES, SHELLS, OR OTHER HARD PARTS.  STROMATOLITES

PALEOZOIC ERA  600 M.Y.A. – 230 M.Y.A.  SUPERCONTINENT PANGEA FORMED  NEW MOUNTAIN RANGES  AGE OF INVERTEBRATES  7 PERIODS (CAMBRIAN, ORDIVICIAN, SILURIAN, DEVONIAN, MISSISSIPPIAN, PENNSYLVANIAN, PERMIAN)  ORGANISMS DURING ERA: TRILOBITES, BRACHIOPODS, FISH, LAND PLANTS, AMPHIBIANS, GIANT COCKROACHES AND DRAGONFLIES.  MADE MOVE TO LAND!  MASS EXTINCTION MARKED END OF ERA

MESOZOIC ERA  230 M.Y.A. – 70 M.Y.A.  PANGEA BROKE UP, FORMING SEPARATE CONTINENTS.  AGE OF REPTILES  LIZARDS, TURTLES, CROCODILES, SNAKES, DINOSAURES, BIRDS.  3 PERIODS (TRIASSIC, JURASSIC, CRETACEOUS)  MASS EXTINCTIONS MARK END OF ERA  CLIMATE: WARM AND MOIST  ANDES, AND ROCKIES FORMED

CENOZOIC ERA  70 M.Y.A. – PRESENT  CONTINENTS SIMILAR TO HOW THEY ARE TODAY  ALPS, HIMALAYAS FORMED  ICE AGES  AGE OF MAMMALS! WHY DO YOU THINK MAMMALS BECAME THE DOMINANT ORGANISMS OF EARTH DURING THIS TIME?  2 PERIODS: (TERTIARY, QUATERNARY) ICE AGE SEPERATES THE TWO  7 EPOCHS (Paleocene, Eocene, Oligocene, Miocene, Pliocene, Pleistocene, Holocene)

HOW DO WE KNOW ALL OF THIS FOSSILS, HALF LIFE, LAW OF SUPERPOSTION

FOSSILS FOSSILS: THE REMAINS OR TRACES OF ANIMALS OR PLANTS FROM A PREVIOUS GEOLOGIC TIME PRESERVATION: MUMMIFICATION, AMBER, TAR BEDS, FREEZING Trace Fossils – tracks, footprints, borings, and burrows Molds, Casts, and imprints Caprolites – fossilized poo Gastroliths – stones in stomach to help grind up food.

WHERE DO YOU LOOK FOR FOSSILS?  Places where there is running water  Places where weathering is minor

LAW OF SUPERPOSITION (relative dating) PRINCIPLE THAT STATES THAT AN UNDEFORMED SEDIMENTARY ROCK LAYER IS OLDER THAN THE LAYERS ABOVE IT AND YOUNGER THAN THE LAYERS BELOW IT.

Radioactive Dating  radioactive isotopes ("parents") that spontaneously decay to form new isotopes ("daughters") while releasing energy. For example, decay of the parent isotope Rb-87 (Rubidium) produces a stable daughter isotope, Sr-87 (Strontium), while releasing a beta particle (an electron from the nucleus). ("87" is the atomic mass number = protons + neutrons.)  _ClocksInRocks.html _ClocksInRocks.html

RADIOACTIVE DATING (absolute age) ELEMENTS IN ROCK EMIT RADIOACTIVE PARTICLES AT A CONSTANT RATE ACTING AS A NATURAL CLOCK EXAMPLE: CARBON 14 IS A RADIOACTIVE ELEMENT THAT DECAYS AT A RATE OF HALF ITS MASS IN 5,730 YEARS. IF I HAD 20 GRAMS OF CARBON 14 IN 11, 000 YEARS HOW MUCH WOULD I HAVE? 5 GRAMS!

RADIOACTIVE DATING A FOSSIL OF THE OLDEST KNOWN ORGANISM WAS FOUND IN A CAVE – ANALYSIS SHOWED THAT ONLY 1/8 OF THE ORIGINAL POTASSIUM-40 (K40) REMAINED. POTASSIUM-40 HAS A HALF LIFE OF 1.3 BILLION YEARS. HOW OLD IS THE FOSSIL?

The Origin of Life  Video: Origins (Monday)