(Brief) History of Life

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1 Oldest fossils are 3.5 Ga Cyanobacteria (?) from the Australian Warraroona Group (ancient marine sediments) Bacteria represent the only life on Earth from 3.5 to ~1.5 Ga - and possibly longer Hard to kill off, very resilient - autotrophs (Brief) History of Life Photosynthetic - make oxygen Note: recall archeabacterea may have evolved earlier than photosynthetic eubacteria Recall: oldest evidence of life is 3.9 Ga organic molecules in sediments.

2 Major Change ~2 Ga: Oxygen in the environment! Prior to 2.3 Ga all sediments on Earth are reduced (no O 2 in atm.) Pyrite (FeS 2 ) and uranite (UO 2 ) sands prevalent thus no free oxygen in the environment. Oxygen is the Great Electron Thief! If you have extra electrons, free oxygen will bond to you (like a clingy boyfriend) = oxidation Sediments younger than 2.3 Ga are oxidized Oxidation of carbon (CO 2 ) Pyrite and uranite no longer in sediments red-beds begin to occur in geologic record

3 Major Change ~2 Ga: Oxygen in the environment! So, before 2.3 Ga O 2 was not concentrated in atmosphere. What little was present, oxidized the crust (SINK = oxidizing Fe in crust) by 2 Ga the sink was filling-up : The crust was oxidized and oxygen became concentrated in the atmosphere Red sandstones form because there is a surplus of O 2 : any exposed Fe is oxidized.

4 Oxygen is toxic to most life prior to ~2 Ga (anaerobic) Once cyanobacteria filled O 2 sinks, O 2 began accumulating in the atmosphere ~O 2 killed off many bacteria Except those that could escape into crust or become aerobic! Rise of the Eukaryotes! Great Oxygen Holocaust

5 Rise of the Eukaryotes! How? symbiosis Acritarchs Bacteria 1.85 Ga fist Eukaryote fossils (large, >60 micron) Acritarchs - Unicellular, photosynthetic, Eukaryotes Unicellular life (Bacteria & Acritarchs) dominate for another ~1 Ga

6 Which is the oldest evidence of life A. Stromatilites (algal mats) B. Fossilized bacterial structures C. Dinosaur fossils D. Carbon-bearing minerals with isotopic composition indicative of organic matter. E. I have no earthly idea on Earth?

7 Marine Productivity Oceans are brimming with life Not a lot of diversity But a great abundance of organisms And very efficient producers (protista or plankton) Sat. image of chlorophyll Production = synthesis of organic molecules from inorganic compounds (autotrophs)

8 Primary Producers = base of food web Primary Producers synthesize organic molecules from inorganic nutrients (phytoplankton) Feed other organisms (zooplankton) Most are photosynthetic - previous map of chlorophyll = map primary production

9 How do they produce Photosynthesis Sunlight + 6CO 2 + 6H 2 O => chlorophyll => glucose (C 6 H 12 O 6 ) + 6O 2 Glucose is used by both autotrophs and heterotrophs to Grow the organism Energy in Respiration Respiration How organisms get energy from glucose (C 6 H 12 O 6 ) + 6O 2 => 6CO 2 + 6H 2 O + Energy (H)

10 Productivity in oceans Chlorophyll content = productivity of photosynthetic organisms (mostly phytoplankton) Note: not the same everywhere High on some parts of coasts Higher at high latitudes What causes variations in productivity? Average annual chlorophyll

11 Requirements for productivity: Sunlight: Most primary producers are photosynthetic Live in photic zone Nutrients: Nitrogen & Phosphorous must be available N (as nitrate or NO 3 ) Used in making proteins = building blocks of life P as phosphate (PO 4 ) Required for DNA Use to make cell walls Required in Respiration Stable water column No vertical mixing when nutrients are present

12 Production in Coastal Areas Estuaries have high nutrient levels due to (1) river input and (2) recycling of nutrients due to flow of fresh and salt water. Ekman flow results in coastal upwelling that brings nutrients to surface

13 Equatorial Pacific Pacific Surface water diverges at equator (due to Eckman flow), bringing nutrients to surface Notice areas of convergence (gyres) have low productivity

14 Short summer But, long summer days Big Bloom - Why so big? Nutrients brought to surface during winter overturn Stable upper water column during summer Melting sea ice No vertical mixing Perfect for phytoplankton bloom! Productivity at High Latitude

15 Mid-Latitude Productivity Combining Solar radiation and nutrient availability (mid-latitude): Nutrients are high in winter b/c of vertical mixing, and low in summer due to consumption by producers Notice biomass lags behind nutrients - b/c of required solar radiation animation

16 Compare productivity in the oceans Upwelling zones (high latitude and coastal): Greatest Primary Productivity Lowest total Primary Productivity - small area Concentrated in space and time (upwelling & Coastal) Good eatin Yum Yum Open oceans: Lowest Primary Productivity Greatest total Primary Productivity - vast size Diffuse or low concentration - not good eatin

17 Compare marine productivity to terrestrial productivity Upwelling zones and Estuaries approach productivity of the most productive cultivated Land! Their productivity is similar to rain forests! Estuaries and upwelling zones are DENSE with life!

18 Which is not required for primary production? A. Nutrients B. Sunlight C. Stable water column

19 Marine food webs begin here: This is basically a map of phytoplankton Phytoplankton Photosynthetic organisms convert inorganic molecules to organic molecules base of the marine food web (supply nutrients to nearly all other organisms!)

20 First link in all marine chains: Zooplankton Zooplankton are herbivore plankton Most numerous and massive population of herbivores on Earth Zooplankton are the primary consumers Convert all plant life to animal tissue Feed all Carnivores (directly or indirectly) Krill

21 Food Web Example: Herring Web = complex interconnected chains Webs = pathways of nutrients & energy Notice: Organisms feed at various levels Organisms occupy various levels during life cycle Disruption of one level, effects all other levels because it disrupts the transfer of nutrients to higher tropic levels! Marine food web - shifting baseline

22 Example: Antarctic food web Humans hunted baleen whales to near extinction. This disrupted Energy transfer to killer whales What was the result? Over harvesting of lower levels! lots of mass required to replace the energy transfer lost by declining whale numbers Disrupted food web & nutrient cycling? What to eat? Leopard Seal

23 Trophic Pyramids Input nutrients & solar E at base (phytoplankton) Nutrients & energy lost to environment at each level Bacteria cycle nutrients back to base! Trophic levels: numbers & mass decrease, size of organism increases Energy transfer between trophic levels: 10% (90% loss to metabolism, life, decay) To produce 10 kg of salmon requires 100 kg fish to feed salmon, 1000 kg zooplankton to feed the fish, kg phytoplankton to feed the zooplankton

24 Review Questions Oxygen in the atmosphere How do oxidized sediments and banded iron forma7ons (BIF) indicate when our atmosphere became oxygen- rich? What effect did the rise of oxygen have on life? What is respira7on and photosynthesis - what do each consume and produce What is primary produc7on Compare the produc7vity of the oceans at various la7tudes - what controls produc7vity correla7ons with la7tude? Why are coastal regions so produc7ve? How and why does produc7vity vary with the seasons? Compare and contrast phytoplankton with zooplankton. What is a food web, and what is at the base of most marine food webs? Why are trophic pyramids wider at the base than the top? How is energy lost and transferred at any level in a trophic pyramid Where do nutrients come from? How does disrup7ng any level of a food web effect the other levels? What type of organism is at the base of hydrothermal food webs?