Origin & History of Life

Transcription

1 Origin & History of Life SIX Kingdoms! New one = Archea Thanks C. Woese Prokaryotes = no discrete nucleus containing genetic material This bush of life accurately shows Archea, Eubacteria and Eukaryotes diverging from single point (x). What is not accurate is that it is now believed that Archea are evolutionarily closer to Eukaryotes than to Eubacteria Major divisions: Kingdoms x Prokaryote Some are extremophiles Live in hot springs, hydrothermal vents, glacial ice More next lecture Some are Chemotrophic S- or CH 4 - reducing Archaeobacterea 1

2 Eubacteria Prokaryote true bacteria Includes Cyanobacteria (blue - green algae) = pond scum Euacteria & Archea = 50% of all organic matter! 1 x 10 6 bacteria per cc water! Eukaryotes - have nucleus with genetic material Unicellular to simple multicellular Most Algae are protist phytoplankton are protist (diatoms & foraminifera) Protista 2

3 Autotrophs - synthesize own food (primary production) Photosynthetic - combine solar energy with nutrients to grow tissue Chemotrophic - extract energy from chemical reactions. These form the base of food web!!! All of the archaeobacterea, some eubacteria, some of the protista All plants Heterotrophs - eat other organisms Herbivores, carnivores, omnivores Detrivores = filter organic matter from sediment = deposit feeders (worms) from water = filter feeders (coral, sponges) Respiration = oxidation of organic molecules to produce energy These organisms rely directly or indirectly on primary producers Some eubacteria, most of the protista, All fungi and animalia Mode and mobility Pelagic organisms live in water column Planktonic = float Nektonic = swim Benthic organisms live on substrate Epifaunal = live on surface Enfaunal = live in substrate (burrow) 3

4 When did life begin on Earth? A. After plate tectonics began to operate, and oceans formed (after ~4.4 Ga) B. ~ 1.75 Ga - the oldest macro fossils found C. ~600 Ma - the first fossil animals D. ~6000 BC - strict creationist view E. I have no earthly idea Origin of Life on Earth: What we know Oldest fossils are 3.5 Ga bacteria First evidence for life come from 3.9 Ga sediments containing apparent organic molecules with abundant 12 C - a product of photosynthesis. Life began (at the latest) 1 Ga after planet condensation Early atmosphere Reducing environment (No O 2 ) No ozone, UV-B radiation! Rich in CH 4, NH 3, CO 2, N 2 Primordial Soup... video Origin of Life: New Hypothesis Carl Woese: new discovery DNA of archeabacteria indicate they are different than eubacteria Why are they called Archeabacteria ( old bacteria )? They diverged from the bush of life long ago (genetically, they are varied and complex - i.e. been around a while) Possibly back when life evolved on Earth in the deep oceans. Question: when did Earth first have oceans? 4.4 Ga Maybe life started long before first fossil (3.5 Ga), or before oldest evidence of life (3.9 Ga) 4

5 Origin of Life: Traditional Concept Miller & Urey, 1953 Simulated a reducing atmosphere and primordial ocean added energy Lightening, volcanic, solar radiation, etc. Results: Formed 12 of 20 amino acids in life Other organic molecules too (HCN, Formaldehyde) Later Fox s experiments made polymers of amino acids Proteins RNA! Fatty acids & lipids - required for cells Conclusion: Not hard to make simple organic molecules Problem with life evolving near surface of Earth: that nasty UV-B! Note: 74 amino acids, and polymers found in Chondritic meteorites. Recall Hydrothermal Vents? Vent Communities Discovered 1976 on the Galapagos Spreading Center Now known on all mid-ocean ridge systems What are all the heterotrophs eating down there? The primary producers in this environment are chemotrophic Bacteria Get energy from reducing methane and sulfur Do not rely on sunlight! Origin of Life: New hypothesis Amino acids around vents Extraterrestrial, or Generated at vent (heat Energy) as in Miller- Urey experiments Why at vent and not surface? Deep sea is shielded from UV-B! Pyrite (FeS 2 ) is abundant in this environment and can serve as catalyst for replicating RNA Huber & Wächtershäuser 1997 Current debate: did life originate at hot, or cold vents? Hot vents may be too hot, too energetic. Cold vents can generate energy required as well as fuels of life from chemical reactions within the crust Branscomb & Russell, 2012, Russell et al., 2010,

6 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 eucteria Recall: oldest evidence of life is 3.9 Ga organic molecules in sediments. First macro fossils Stromatolites = algal mats or communities of cyanobacteria (photosynthetic! Produce oxygen) Appear in the geologic record ~ 1.75 Ga Stromatolites are the only mega fossils from Precambrian time (Time > 570 Ma). 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 6

7 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. Major Change ~2 Ga: Oxygen in the environment! Banded Iron Formations (BIF) Span 3.5 to 1.9 Ga (few, odd younger ones) BIF are marine chemical sediments (precipitation from the ocean) Oxidized-and Reduced Iron (magnetite and hematite) interbedded with chert Fe is soluble in reducing oceans. And becomes insoluble as oceans become oxidizing. So, BIF precipitation from Ga indicates change from reducing to oxidizing conditions in the oceans. Near cessation of BIF by ~1.9 Ga indicates Oxygen sinks of crust are full Oxygen in oceans high All Fe is precipitated from oceans Oxygen is toxic to most life prior to 1.9 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 7

8 Rise of the Eukaryotes! How? symbiosis Bacteria Acritarchs 1.85 Ga fist Eukaryote fossils (large, >60 micron) Acritarchs - Unicellular, photosynthetic, Eukaryotes Unicellular life (Bacteria & Acritarchs) dominate for another ~1 Ga Cambrian Explosion! ~ 600 Ma Multicellular life begins in Cambrian time Darwin s Dilemma Abundant multicellular fossils younger than 570 Ma Rocks greater than 570 Ma Void of multicellular Life Escape of Darwin s Dilemma Tyler ~ microfossils in 2 Ga Gunflint Fm CAN Sprigg ~ 1946 Ediacara in 600 Ma Rawnsley qtz AUS Point: life did abound before Cambrian, just small or poorly preserved What Caused Cambrian Explosion? Don t know. Likely combination of many reasons, including: Global glaciation caused extinction acritarchs (open niches) Massive rise in O 2 (>6%) Fast plate spreading rise in sea level increased nutrients 8

9 Now life takes off Diversity increases- number of genera grows over time Punctuated by extinctions: compare Permian to K-T Note: all early life is marine! Increasing Diversity of Marine Life Some modern fauna appear in Cambrian (bryozoa, bivalves, gastropods) Most modern fauna don t appear until Silurian and Devonian (Fish and plants) Old fish and plants Now we can begin to look at modern marine life (note: terrestrial life does not begin until after Silurian time ~400 Ma!) 9

10 Which is the oldest evidence of life on Earth? 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 Where did life begin on Earth? A. The Oceans B. The Atmosphere C. Lakes and streams D. Continental surface E. I have no earthly idea Review Questions Why are Archeabacteria a sixth kingdom of life and not part of the kingdom Eubacteria? How are prokaryotes different from eukaryotes? To which kingdom do phytoplankton belong? From this, what do you know about phytoplankton? What is the first evidence for life on Earth and how old is it? What can you conclude from the Fox-Miller-Urey experiments regarding the origins of life? What new discoveries have altered this hypothesis, and What is the favored hypothesis for the origins of life on Earth? Oxygen in the atmosphere How do oxidized sediments and banded iron formations (BIF) indicate when our atmosphere became oxygen-rich? What effect did the rise of oxygen have on life? 10