Presentation on theme: "Geologic Time & Earth’s Evolution"— Presentation transcript:
1 Geologic Time & Earth’s Evolution Piecing together Earth’s historyRelative DatingUsing laws of superposition, cross cutting, etc. to determine a sequence of events (this happened, then that)Index Fossils – constrain (pin down) a time range when a rock layer was deposited.Fossils of extinct organisms, that were wide spread, and lived during a specific period of time.Example: Trilobites
3 Ch 23.6: Geologic Time & Earth’s Evolution Piecing together Earth’s historyAbsolute DatingRadioactive elements in rocks, like uranium, potassium, carbon, breakdown at a known rate. If you know how much was in the initial sample … you can determine age. (Isotopic dating)How Earth was Made, Part 1:
4 Ch 23.6: Geologic Time & Earth’s Evolution ERAS & PERIODSWhy all the divisions?To manage Earth’s history, geologists have divided Earth’s history into EONS. Eons are divided into ERAS. Eras are divided into PERIODS. Periods are divided into EPOCHS.You need to know the major developments in terms of life forms, tectonics, atmosphere and climate for each ERA.
5 Geo. Time is broken up into ERAS (based on life forms and enviro.) Cenozoic (now – 65 mya)Mesozoic (254 ma)Paleozoic (540 ma)All time before that = Precambrian (540 ma – 4.6 billion)ERAS are NOT EQUAL in TIME.The Precambrian was the longest ERA. It took Earth a LONG time to be suitable for complex life.Each era ends with a mass extinction followed by a burst of speciation.
6 Mass Extinctions: Punctuate E’s History Between each Era (and some periods)
7 Mass Extinctions = High % of species go extinct Species that are better suited to environment are successful, reproduce, and evolve.Causes: Meteor impact; Volcanism; Glaciation; anything that can change atmosphere, climate, or environmental conditions.
8 CH 23.6 Geologic Time and Earth’s Evolution Complex multicellular life is a “recent” development.
9 PrecambrianFossils from this time are not abundant in the rock record because most organisms are “soft bodied” – no skeletons or shells.
10 Precambrian: 4.5 billion – 540 ma Earth starts off as MOLTEN and VOLCANICAtmosphere = CO2, CH4(methane), H2O= Green house gasesOceans form and first continents form when Earth coolsOrigin of water = volcanic steam & meteorites (comets)1st life = bacteria (single celled) 3.5 bya - use chemosynthesis (not sunlight) for energy. They can withstand extreme conditions.
11 Precambrian: 4.5 billion – 540 ma Cyanobacteria (blue-green algae)~ 3 bya – take in CO2 and release O2 (photosynth) PLANET CHANGING!Temps. Decrease (take in CO2)Oxygen makes O3 = OZONE LAYER Shields surface from UV radiation (UV kills cells)O2 atmosphere– more complex organisms to develop!Simple multicellular organisms in shallow seas1st Supercontinent (Rhodinia)MASS EXTINCTION = SNOW BALL EARTH ICE AGE! Closes PRECAMBRIAN
13 Paleozoic Era: 540 – 245 myaCAMBRIAN EXPLOSION starts off ERA – “explosion” in the diversity of life formsSnowball Earth is thawed by millions of years of volcanic activity.Warm temperaturesLIFE IN SHALLOW SEAS½ through, life “invades” land (amphibians, land plants, insects) (Thank you Ozone)
14 Paleozoic Era: 540 – 245 myaEarly GIANT FORESTS/Swamps become our fossil fuels (Buried, but not decomposed plant and animal matter fossil fuels)Pangaea assembles Interior of continent becomes DRY and COOL(favors reptiles etc)Ends with…MASS EXTINCTION = “GREAT DYING”Volcanic activity? Lava flows in Siberia for millions of years change climate?
18 Cenozoic Era: 65 mya - present AGE of MammalsICE AGES – Glaciers advance and retreatOcean currents change due to new continent positions; Mt. Building changes air circulationHominids (human ancestors) – 2 mya; Modern humans – 200,000 yrsGlobal Mountain building - affect air circulation drier & cooler conditionsCooler & Drier Grasslands (not tropical forests)When glaciers grow …Sea level dropsMore land is exposed (land bridges)Ends with… ?????
19 What does a mass extinction look like in the Rock Record? Black layer = carbon rich; carbon from organisms that died abruptly and could not all be decomposed; carbon in organism changes w/heat and pressure to become oil/coal.White layer = Debris from asteroid/impact
20 Meteoroid that hit 65 mya caused a Mass Extinction 75% Species on planet go extinct.90% of planktonic life in ocean die (plankton supports the oceanic food chain).Takes 10,000 years to recover.
23 How do we know when Meteoroids have hit Earth in the Past? Look for … in the rock layerIridium – an element not common on Earth but common on meteroids (asteroids or comets)Shocked Quartz – heat changes quartz grainsTektites - quartz grains vaporized and cooled so fast they turn in to glass beads.K-T Boundary: This layer is found on every continent in rocks 65 my old.
24 K-T ExtinctionWhen: 65 million years ago (End of Cretaceous- Beginning of Tertiary Periods) Where: Chicxulub – Yucatan Pennisula Mexico What: Asteriod or Comet – 10km in diameter makes a crater 180 km in diameter. Impact Event: 100 MillioMegatons TNT (6 x more energetic than 1980 Mt. St. Helen’s eruption) Results– Fires; Magnitude 10 Eqs; Tsunamis; Climate change; Volcanism; Mass extinction (collapse of ocean food chain & bye-bye dinosaurs)