DOC PREVIEW
UW ATMS 211 - Earth History

This preview shows page 1-2-3-4 out of 11 pages.

Save
View full document
View full document
Premium Document
Do you want full access? Go Premium and unlock all 11 pages.
Access to all documents
Download any document
Ad free experience
View full document
Premium Document
Do you want full access? Go Premium and unlock all 11 pages.
Access to all documents
Download any document
Ad free experience
View full document
Premium Document
Do you want full access? Go Premium and unlock all 11 pages.
Access to all documents
Download any document
Ad free experience
View full document
Premium Document
Do you want full access? Go Premium and unlock all 11 pages.
Access to all documents
Download any document
Ad free experience
Premium Document
Do you want full access? Go Premium and unlock all 11 pages.
Access to all documents
Download any document
Ad free experience

Unformatted text preview:

Lecture 24:We’ve made it through the Precambrian.Now we’re in the Phanerozoic: 544 Ma to present-dayWhere we’re going:-Review marker events in Earth history-Mesozoic (251-65 Ma) Warmth (p.245-251)-Cenozoic (65 Ma-present) Cooling- Pleistocene (2 Ma-present) glacial cycles (Chapter 14)-Climate of the last millennium (Chapter 15)Weeks 8,9,10-Climate of the 20th century- Global Warming: science and policy issuesEarth History: Review of Marker Events1. Origin of Earth2. Origin of Life3. First Rise of Oxygen First set of Snowball Earths4. Second Rise of Oxygen Second set of Snowball Earths5. Ediacaran fossils Cambrian Explosion of fossils6. Biggest Animal Extinction7. Asteroid extinction of dinosaurs8. Beginning of modern glaciations/ interglacials9. End of last ice-age4.56 Gadon’t know; some time before 3.8 Ga2.4-2.2 Gaabout 800-600 Ma575 Ma (perhaps as old as 590 Ma)544 Ma65 Ma2.5 Ma12 ka251 MaHow I remember all the geological agesCamelsonlysitdowncarefully,Perhapstheirjointscreak.Perhapsearlyoilingmightpreventpermanenthardening.CambrianOrdovicianSilurianDevonianCarboniferousPermianTriassicJurassicCretaceousPaleoceneEoceneOligoceneMiocenePliocenePleistoceneHolocene.PeriodsEpochsYou don’tabsolutely needto knowthis but it does helpMesozoic Warmth (251-65 Ma)Climate: - Warmer global-mean temperature. - Much warmer Polar Regions; no ice-caps. - Much warmer deep ocean: 15°C vs. 2°C today.Evidence: - Lush ferns and alligators in Siberia. Dinosaurs in Alaska. - Oxygen isotopes in oceanic carbonatesCause: - Higher CO2 is leading suspect. - sea-floor spreading rate was greater - higher sea level (no ice caps): less land for weatheringMesozoic climate mystery:The eq.-to-pole temperature gradientwas very small (above Fig). Somehoweq.-to-pole heat transport was veryefficient or the greenhouse effect wasenhanced at the poles by high clouds.The era of dinosaursFig 12-14. 100 Ma zonally-averaged tempCarbon isotopes as CO2 indicatorsOrganisms preferentially take up 12CBut if CO2 is low, photosynthesizers will extract whatever C atomsthey can get, whether 12C or 13C(a “beggars can’t be choosers” isotope rule)warmer, moreCO2colder, lessCO2At low CO2, experiments show more 13C in organic matter thanwith abundant CO2.Fig 12-15Cenozoic cooling, 65 Ma to presentWhat: - Earth cools after 80 Ma. - Life retreats from poles. - Polar ice caps form. - Eventually, ice-ages begin.Why (one leading theory): - initial decrease due to slower midocean ridge spreading- Then India collides with Asia at 40-30 Ma. - Himalayas form. - Silicate weathering increases. - Atmospheric CO2 goes down.Pleistocene (1.8 Ma-10 ka) glacial cyclesMaximum ice extent(Seattle under 1 kmof ice.)Glacier indicators:- striations,- till / morainesAlso some of the tillis fine silt (~0.01 mm)and gets transported anddeposited by the wind.Deposits are called loess.Fig 14-1Oxygen Isotopes: Evidence for Temperature16O vs 18O"light"(normal)"heavy"• evaporation favors "light” 16O• condensation (precipitation) favors "heavy” 18OMore 18O in ocean carbonates records glacial ice volume:More 16O-enriched water in ice-sheets means remaining ocean is "heavier".Less 18O in ice-cores indicates colder temperature:Colder conditions means more precipitation en route so isotopically "lighter" snow (precipitation leaves water vapor for snow enriched in 16O)Fig 14-33.5 Million Year Record of Global Ice VolumeQuestions 1. Is this an ocean sediment record or a polar ice-core record? TIME 1. Ocean sediments record ice volume. Ice-core records only extendback to about 500,000 years.Now3.5 Million Year Record of Global Ice VolumeQuestions: 2. What two major transitions do you see in this record? 3. Was sea-level lower or higher than today during the three most prominentprevious interglacial periods?Ice-agesbeginOscillations get longer& larger, starting 0.6-0.7 MaTIME 3. Less ice-volume, therefore higher sea level. (May have been warmer than today as


View Full Document

UW ATMS 211 - Earth History

Download Earth History
Our administrator received your request to download this document. We will send you the file to your email shortly.
Loading Unlocking...
Login

Join to view Earth History and access 3M+ class-specific study document.

or
We will never post anything without your permission.
Don't have an account?
Sign Up

Join to view Earth History 2 2 and access 3M+ class-specific study document.

or

By creating an account you agree to our Privacy Policy and Terms Of Use

Already a member?