Presentation on theme: "Piecing together Earth’s history 1.Relative Dating A.Using laws of superposition, cross cutting, etc. to determine a sequence of events (this happened,"— Presentation transcript:
Piecing together Earth’s history 1.Relative Dating A.Using laws of superposition, cross cutting, etc. to determine a sequence of events (this happened, then that) B.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 Geologic Time & Earth’s Evolution
Relative Dating: Index Fossils
Piecing together Earth’s history 2.Absolute Dating Radioactive 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: Ch 23.6: Geologic Time & Earth’s Evolution
ERAS & PERIODS Why 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.
Geo. Time is broken up into ERAS (based on life forms and enviro.) 1.Cenozoic (now – 65 mya) 2.Mesozoic (254 ma) 3.Paleozoic (540 ma) 4.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.
Mass Extinctions: Punctuate E’s History Between each Era (and some periods)
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.
CH 23.6 Geologic Time and Earth’s Evolution Complex multicellular life is a “recent” development.
Precambrian Fossils from this time are not abundant in the rock record because most organisms are “soft bodied” – no skeletons or shells.
Precambrian: 4.5 billion – 540 ma Earth starts off as MOLTEN and VOLCANIC Atmosphere = CO 2, CH 4 (methane), H 2 O= Green house gases Oceans form and first continents form when Earth cools Origin of water = volcanic steam & meteorites (comets) 1 st life = bacteria (single celled) 3.5 bya - use chemosynthesis (not sunlight) for energy. They can withstand extreme conditions.
Precambrian: 4.5 billion – 540 ma Cyanobacteria (blue-green algae) ~ 3 bya – take in CO 2 and release O 2 (photosynth) PLANET CHANGING! Temps. Decrease (take in CO2) Oxygen makes O 3 = OZONE LAYER Shields surface from UV radiation (UV kills cells) O 2 atmosphere– more complex organisms to develop! Simple multicellular organisms in shallow seas 1 st Supercontinent (Rhodinia) MASS EXTINCTION = SNOW BALL EARTH ICE AGE! Closes PRECAMBRIAN
Paleozoic Era: 540 – 245 mya CAMBRIAN EXPLOSION starts off ERA – “explosion” in the diversity of life forms Snowball Earth is thawed by millions of years of volcanic activity. Warm temperatures LIFE IN SHALLOW SEAS ½ through, life “invades” land (amphibians, land plants, insects) (Thank you Ozone)
Paleozoic Era: 540 – 245 mya Early 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?
Mesozoic Era: mya AGE of DINOs WARM and subtropical environment Virtually ice-free Pangaea rifts apart 1 st Flowering plants; Giant insects; birds Mammals appear (small) Ends with… MASS EXTINCTION = ASTEROID IMPACT = K-T EVENT (+ Lava flows in India) Meteoroid impact in the Gulf of Mexico
Cenozoic Era: 65 mya - present AGE of Mammals ICE AGES – Glaciers advance and retreat Ocean currents change due to new continent positions; Mt. Building changes air circulation Hominids (human ancestors) – 2 mya; Modern humans – 200,000 yrs Global Mountain building - affect air circulation drier & cooler conditions Cooler & Drier Grasslands (not tropical forests) When glaciers grow … Sea level drops More land is exposed (land bridges) Ends with… ?????
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
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.
How do we know when Meteoroids have hit Earth in the Past? Look for … in the rock layer 1.Iridium – an element not common on Earth but common on meteroids (asteroids or comets) 2.Shocked Quartz – heat changes quartz grains 3.Tektites - 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.
K-T Extinction When: 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)
Human Evolution & Hominids html Evolution of Early Humans human.html Cave paintings uvet/en/ Evolutionary Tree tc.pbs.org/wgbh/nova/beta/assets/img/the- adaptable-human/image-05-large.jpg