PTYS 214 – Spring 2011  Next week is Spring Break – NO CLASSES  Class website: /  Useful Reading: class website  “Reading Material” Announcements

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

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 Gyr old rocks (Pilbara, Australia)

Atmospheric Oxygen All terrestrial life requires energy, carbon and nutrients, and liquid water Why is atmospheric oxygen important for life? 1.All terrestrial multicellular life requires high O 2 CH 2 O + O 2 → H 2 O + CO 2 + energy 2.Almost all terrestrial life requires some protection from UV

Ozone: the Good and the Bad 90% 10%

Stratospheric Ozone Most of the ozone is in the stratosphere (above 15 km) Production: O 2 + (UV radiation < 240 nm) → 2 O O + O 2 → O 3 Destruction: O 3 + (UV radiation nm) → O 2 + O O 3 + O → 2O 2 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

Tropospheric Ozone In the troposphere ozone is the result of pollution: OH + CO pollution → H + CO 2 H + O 2 → HO 2 HO 2 + NO pollution → OH + NO 2 NO 2 + hν → NO + O O + O 2 → O 3 Net reaction: CO + 2O 2 → CO 2 + O 3 The Bad Ozone is a very chemically active gas and can cause eye and respiratory problems

Both O 2 and O 3 are important to the biosphere but O 3 cannot form without O 2 What are natural sources of O 2 ?  Volcanoes: NO Major volcanic gases are H 2 O, CO 2, SO 2 etc., but no O 2  Today the major source of O 2 is LIFE H 2 O + CO 2 → CH 2 O + O 2 Atmospheric Oxygen! Mt. Pinatubo eruption, 1991

Oxygen Sources CO 2 +H 2 O  O 2 + CH 2 O 2H 2 O+hν  O 2 + 4H Space Ocean Atmosphere Hydrogen escape Organic carbon burial Photosynthesis Water dissociation (minor)

Oxygen Sinks Oxidation of reduced gases O + H 2 O  H 2 O 2 SO 2 + H 2 O 2  H 2 SO 4 Oxidative weathering of rocks Fe 2+  Fe 3+ (FeO  Fe 2 O 3 ) Atmospheric O 2 Outgassing (volcanoes) SO 2, H 2 S, H 2 Aerobic Respiration CH 2 O+O 2  CO 2 + H 2 O Methane Oxidation CH 4 + O 2  CO 2 + 2H 2 Ocean Land

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

When did life start to produce O 2 ? Molecular biomarkers  Earliest biomarkers for cyanobacteria and eukaryotes: ~ Gyr ago Maybe some photosynthetic O 2 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

2.47 Gyr old Brockman Iron Formation, Western Australia Alternating iron-rich layers and iron- poor shale or chert layers Iron-rich: include iron oxides (Fe 3 O 4 or Fe 2 O 3 ) formed in the oceans by combining oxygen with dissolved iron Iron-poor: deep ocean should have been anoxic, causing deposition of shales and cherts BIFs Varying O 2 amount

Rounded detrital uraninite from ca. 2.7 Ga Witwatersrand Basin, South Africa Rounded detrital pyrite from ca. 2.6 Ga Black Reef Quartzite, South Africa Uraninite (UO 2 ) and pyrite (FeS 2 ) are unstable under high O 2 levels in the atmosphere  If in contact with the atmosphere (detrital), they can only form in an O 2 -poor atmosphere Detrital Uraninite and Pyrite

Hekpoort Paleosol, South Africa (about 2.22 Gyr old) Paleoproterozoic Redbeds, ON, Canada Reddish color is due to hematite (Fe 2 O 3 )  presence of O 2 Oldest Redbeds are about 2.3 Gyr old Paleosols prior to 2.3 Gyr ago lost their iron (no oxygen to form hematite) Paleosols and Redbeds

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

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

The O 3 layer should have been absorbing most UV radiation by 2.3 Ga, as soon as O 2 levels began to rise What About Ozone (O 3 )? O 2 rise causes O 3 rise! An O 2 level of 1% PAL is sufficient to create a sufficient ozone screen

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) Slow Early Evolution…

All known complex multicellular organisms need at least 10-20% of the present oxygen 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!)

Forest Fires and Atmospheric Oxygen CH 2 O + O 2 → CO 2 + H 2 O Fires produce charcoal that is preserved in the geologic record

There has been a continuous record of charcoal in sediments younger than 360 million years old  O 2 levels have not been lower than 15% during the past 360 million years Present Atmospheric Level 0% 10% 20% 30% Atmospheric oxygen 21% 15% Fire

Summary of the O 2 Constraints (Goldblatt et al., 2006) Great Oxidation Event Low-Fe Paleosols Redbeds Detrital Uraninite Pyrite BIFs Eucaryotes P.A.L. = Present Atmospheric Level

Atmospheric Oxygen Summary ~1ppm No O 2 /O 3 A few% 15-35%

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? Gyr ago) Single-celled organisms, prokaryotes (cyanobacteria) and some eukaryotes

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

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

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

No logistic growth curve in the fossil record! Why?

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 Species Crust Sediments

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 )

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!

Mass Extinction Sharp decrease in the number of species in a relatively short period of time 1)It must be a rapid event (from less than 10,000 to 100,000 years) 2)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) 3)Extinct life forms must have came from different phyla, lived in different habitats, spread out over the whole world