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PTYS 214 – Spring 2011

Announcements. PTYS 214 – Spring 2011. Next week is Spring Break – NO CLASSES Class website: http://www.lpl.arizona.edu/undergrad/classes/spring2011/Pierazzo_214 / Useful Reading: class website  “Reading Material” http://www.pnas.org/content/96/20/10955.full

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PTYS 214 – Spring 2011

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  1. Announcements PTYS 214 – Spring 2011 • Next week is Spring Break – NO CLASSES • Class website: http://www.lpl.arizona.edu/undergrad/classes/spring2011/Pierazzo_214/ • Useful Reading:class website  “Reading Material” http://www.pnas.org/content/96/20/10955.full http://en.wikipedia.org/wiki/Mass-independent_fractionation http://en.wikipedia.org/wiki/Fossil_record_of_fire http://en.wikipedia.org/wiki/Great_Oxygenation_Event

  2. Midterm • Total Students: 30 • Class Average: 72.6 • Low: 35 • High: 103 Midterm is worth 20% of the grade

  3. Early Life Summary Evidence of the earliest life on Earth is difficult to prove: • Isotopic evidence seems to date it back to about 3.5 Gyr (Pilbara craton, Australia) • Oldest stromatolites are about 3.46 Gryr old • Earliest microfossils (accepted) date back to about 2.55 Gyr (Transvaal Supergroup, South Africa) • Earliest molecular biomarkers date back to about 2.5-2.7 Gyr old rocks (Pilbara, Australia)

  4. Atmospheric Oxygen All terrestrial life requires energy, carbon and nutrients, and liquid water Why is atmospheric oxygen important for life? • All terrestrial multicellular life requires high O2 CH2O + O2 → H2O + CO2 + energy • Almost all terrestrial life requires some protection from UV

  5. Ozone: the Good and the Bad 90% 10%

  6. Stratospheric Ozone Most of the ozone is in the stratosphere (above 15 km) Production: O2 + (UV radiation < 240 nm) → 2 O O + O2 → O3 Destruction: O3 + (UV radiation 240-310 nm) → O2 + O O3 + O → 2O2 The Good Stratospheric ozone absorbs part of the UV spectrum (<310 nm) where other gases do not absorb  That’s why ozone in stratosphere is good for us UV-C UV-B UV-C

  7. Tropospheric Ozone In the troposphere ozone is the result of pollution: OH + COpollution→ H + CO2 H + O2 → HO2 HO2 + NOpollution → OH + NO2 NO2 + hν → NO + O O + O2 → O3 Net reaction: CO + 2O2 → CO2 + O3 The Bad Ozone is a very chemically active gas and can cause eye and respiratory problems

  8. Both O2 and O3 are important to the biosphere but O3 cannot form without O2 What are natural sources of O2? Volcanoes: NO Major volcanic gases are H2O, CO2, SO2 etc., but no O2 Today the major source of O2 is LIFE H2O + CO2→ CH2O + O2 Atmospheric Oxygen! Mt. Pinatubo eruption, 1991

  9. Oxygen Sources Hydrogen escape Space Water dissociation (minor) 2H2O+hν O2 + 4H Atmosphere Photosynthesis CO2+H2O  O2 + CH2O Ocean Organic carbon burial

  10. Oxygen Sinks Atmospheric O2 Aerobic Respiration CH2O+O2 CO2 + H2O Oxidation of reduced gases O + H2O  H2O2 SO2 + H2O2 H2SO4 Outgassing (volcanoes) SO2, H2S, H2 Oxidative weathering of rocks Fe2+  Fe3+ (FeO  Fe2O3) Methane Oxidation CH4 + O2 CO2 + 2H2 Ocean Land Land

  11. Changes in Oxygen Abundance • Oxygen abundance in the atmosphere is a result of the balance between sources and sinks • The atmosphere does not have much mass •  Any lack of balance in sources vs. sinks • results in the immediate changes of the • atmospheric oxygen

  12. When did life start to produce O2? Molecular biomarkers  Earliest biomarkers for cyanobacteria and eukaryotes: ~ 2.5 -2.7 Gyr ago Maybe some photosynthetic O2 flux occurred 2.7 Gyr ago Geologic Evidence  Atmosphere with low oxygen until about 2.3 Gyr ago: • BIFs (Banded Iron Formations) • Detrital Uraninite and Pyrite • Paleosols and Redbeds • Sulfur Isotope Ratios

  13. BIFs Varying O2 amount Alternating iron-rich layers and iron-poor shale or chert layers Iron-rich: include iron oxides (Fe3O4 or Fe2O3)formed in the oceans by combining oxygen with dissolved iron Iron-poor: deep ocean should have been anoxic, causing deposition of shales and cherts 2.47 Gyr old Brockman Iron Formation, Western Australia

  14. Detrital Uraninite and Pyrite Rounded detrital pyrite from ca. 2.6 Ga Black Reef Quartzite, South Africa Rounded detrital uraninite from ca. 2.7 Ga Witwatersrand Basin, South Africa Uraninite (UO2) and pyrite (FeS2) are unstable under high O2 levels in the atmosphere If in contact with the atmosphere (detrital), they can only form in an O2-poor atmosphere

  15. Paleosols and Redbeds Paleoproterozoic Redbeds, ON, Canada Reddish color is due to hematite (Fe2O3)  presence of O2 Oldest Redbeds are about 2.3 Gyr old Paleosols prior to 2.3 Gyr ago lost their iron (no oxygen to form hematite) Hekpoort Paleosol, South Africa (about 2.22 Gyr old)

  16. Sulfur Mass-Independent Fractionation Normally, isotopic ratios of an element follow a standard mass fractionation line (MFL): 33S  0.515×34S Prior to 2.5 Gyr ago the isotope ratios fall off the MFL line! 33S= 33S - 0.515×34S  0 3.3 – 3.5 Gyr old samples S-isotopes: 32S  95% 33S  <1% 34S  4 % 36S  trace 33S>0.51534S 33S<0.51534S Farquhar et al. 2001

  17. Sulfur Mass-Independent Fractionation • Large Sulfur MIF effects are associated with photochemical reactions (involving UV radiation) • Sulfur MIF can only occur in an oxygen-free atmosphere 33S= 33S - 0.515×34S Kump (2008) Nature 451, p.277-278

  18. What About Ozone (O3)? O2 rise causes O3 rise! The O3 layer should have been absorbing most UV radiation by 2.3 Ga, as soon as O2 levels began to rise An O2 level of 1% PAL is sufficient to create a sufficient ozone screen

  19. Slow Early Evolution… Oxygen was in the atmosphere by 2 Gyr ago However, life was limited to unicellular organisms or very simple multicellular organisms until ~540 Myr ago The oldest known possible multicellular eukaryote is Grypania (~1.9 Gyr old)

  20. Cambrian Explosion About 540 Myr ago there was a seemingly rapid appearance of complex multicellular organisms (all we really know about it comes from two main locations!) All known complex multicellular organisms need at least 10-20% of the present oxygen

  21. Fires produce charcoal that is preserved in the geologic record Forest Fires and Atmospheric Oxygen CH2O + O2 → CO2 + H2O

  22. 30% Fire Present Atmospheric Level 21% 20% 15% 10% Atmospheric oxygen 0% There has been a continuous record of charcoal in sediments younger than 360 million years old O2 levels have not been lower than 15% during the past 360 million years

  23. Summary of the O2 Constraints Great Oxidation Event Eucaryotes BIFs Detrital Uraninite Pyrite Low-Fe Paleosols Redbeds (Goldblatt et al., 2006) P.A.L. = Present Atmospheric Level

  24. Atmospheric Oxygen Summary ~1ppm 15-35% A few% No O2/O3

  25. Major steps in the evolution of life Phanerozoic Eon (542 Myr ago - present) “Visible life” (macroscopic animals and plants) Proterozoic Eon (2.5 – 0.54 Gyr ago) Mostly single-celled and some primitive multicellular organisms Archean Eon (3.5? - 2.5 Gyr ago) Single-celled organisms, prokaryotes (cyanobacteria) and some eukaryotes

  26. Phanerozoic Eon Paleozoic Era (250-540 Myr ago) - Cambrian, Ordovician, Silurian, Devonian, Carboniferous, Permian periods - Age of sea life (trilobites) Mesozoic Era (65-250 Myr ago) - Triassic, Jurassic, Cretaceous periods - Age of dinosaurs Cenozoic Era (0-65 Myr ago) - Paleogene, Neogene periods - Age of mammals

  27. The fossil record of biodiversity Species: ability to interbreed, producing fertile offsprings similar morphology (body shape) or DNA Species always form and die due to genetic mutations and natural selection

  28. Logistic Growth Curve Change in number of species = origination rate - extinction rate On average, 10 - 25 new species originate and become extinct each year

  29. No logistic growth curve in the fossil record! Why?

  30. Species Sampling bias! There are much more recent rocks than ancient rocks available to study Possible alternative: Minimize sampling bias by looking at higher taxonomic groups Crust Sediments

  31. Taxonomy Specie: Homo Sapiens (all people) Genus: Homo (humans and close relatives) Family: Hominidae (“great apes”: humans, chimpanzees, gorillas, orangutans) Order: Primates (all apes and monkeys) Class: Mammalia (mammary and sweat glands) Phylum(division): Chordates (vertebrates) Kingdom: Animalia (moving consumers) Domain: Eukarya (complex cells)

  32. Complex Life Earth-like complex life requires not only energy, water, nutrients and carbon but also oxygen and ozone (UV protection) Suppose the environment has everything indicated above (Phanerozoic eon) Does it mean that the animal life will evolve smoothly? No!

  33. Mass Extinction Sharp decrease in the number of species in a relatively short period of time • It must be a rapid event (from less than 10,000 to 100,000 years) • A significant part of all life on Earth became extinct (use of families is more reliable than species; for example extinction of 18% of all families corresponds to about 40% of all genera and 70% of all species) • Extinct life forms must have came from different phyla, lived in different habitats, spread out over the whole world

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