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Life in the Precambrian. Prelude to Us. Major Steps in the Precambrian Evolution of Life. Origin of Life (4.0 - 3.8 Gyrs) Photosynthesis (3.8 - 3.5 Gyrs) Aerobic (Oxygen-based) Respiration (3-2 Gyrs) Eukaryotes / Endosymbiosis (2.1-1.6 Gyrs) Sex / Death (1.2 - 1 Gyrs)
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Life in the Precambrian Prelude to Us
Major Steps in the Precambrian Evolution of Life • Origin of Life (4.0 - 3.8 Gyrs) • Photosynthesis (3.8 - 3.5 Gyrs) • Aerobic (Oxygen-based) Respiration (3-2 Gyrs) • Eukaryotes / Endosymbiosis (2.1-1.6 Gyrs) • Sex / Death (1.2 - 1 Gyrs) • Multicellular Life (1,000 - 800 Myrs) • Skeletons & Shells (600 Myrs) * All dates are approximate
1. Origins Stromatolites - Life’s most successful form
Inorganic to Organic Hurdles • Inorganic production of organic compounds (amino acids, nucleotides, carbohydrates, lipids) • Development of • Genetic Code (from nucleotides) • Proteins (from amino acids) • Metabolism (based on carbohydrates) • Cell Membrane (from lipids)
Organic Compound Formation:Amino Acids 1. “Warm Pond” 2. Space 3. Hydrothermal Vents
Organic Compound Formation:Lipids & Carbohydrates Warm Pond or Hydrothermal Vents Nucleotides Much More Difficult
Small compound combined to form larger ones (polymers) With the help of clay? Clay “Template”
Small compound combined to form larger ones (polymers) Result: RNA? Clay “Template”
Small compound combined to form larger ones (polymers) Evaporation Result: RNA?
Enter the “RNA World” Self-replicating RNA forms the first primitive life RNA codes to make first proteins Proteins help make DNA
Membrane Lipids tend to stick together
Metabolism Heterotrophic (consummers) / Fermentation Why? Simple process(Need to eat before you learn to cook) Present in all organisms Doesn’t require a cell membrane More details to come…
LUCA - Last Universal Common Ancestor(prokaryote, heat-loving, heterotroph) Why? • All life is made of the same organic compounds • All life uses same 20 amino acids (all left-handed) • All life uses the same genetic code (same 4 ‘letters”)
Why is Life Not Re-evolving Today? Oxygen & Predators
Isua Supergroup Oldest Evidence for Life: Isua Supergroup Greenland (3.8 Gyrs)
12C/13C Enrichment in Organics CO2 in Atmosphere (includes 12CO2 and 13CO2 ) 18‰ 12C Enriched (more 12C than atm) 7‰ 12C Depleted(less 12C than atm) 25±10‰ 12C Difference
2. Photosynthesis First Metabolism: Involved Fermentation (Anaerobic Respiration (without Oxygen)) Break down Glucose --> 2 Energy Units (ATP) Start to use up available glucose Natural selection kicks in
Making Glucose Fermentation Glucose Energy Glucose Synthesis Glucose Energy 7 of the 11 step are just reverse of Fermentation
Making Glucose with Sunlight First - Anaerobic Photosynthesis Modified Form of Glucose Synthesis Hydrogen + Carbon Dioxide --> Glucose Second - Aerobic Photosynthesis Modified Form of Anaerobic Photosynthesis Water + Carbon Dioxide --> Glucose + Oxygen Releases Oxygen … more in a minute
First Fossils to Photosynthesize:Cyanobacteria from Apex Chert 3.5 Gyr fossil from the Apex Chert
North Pole, Australia Stromatolite (3.5 Gyrs) Existed on Earth for over 3.5 Gyrs!
Back to Metabolism… 3. Aerobic Respiration Oxygen Oxygen Oxygen Oxygen Gas Warfare - Oxygen is lethal to most existing bacteria = Advantage - removes competition
Aerobic Respiration Three step process - each a modification of earlier form of metabolism However: Burning 1 glucose molecule in the presence of oxygen releases 36 energy units! (Fermentation releases 2 energy units) = Advantage
Gunflint Formation, Canada 1.9 Gyrs
How do we know Oxygen was Increasing? Earth Started to Rust
Evolution of Metabolism 3.8 Gyrs Fermentation (Anaerobic Respiration) Glucose Synthesis Anaerobic Photosynthesis Aerobic Photosynthesis 2.5 Gyrs Aerobic Respiration
4. Eukaryotes & Endosymbiosis Chuaria circularis Tawuia dalensis 800 Myrs Fossil Acritarch First Appear 1.6 Gyrs
Oldest EukaryoteGrypania spiralis 2.1 Gyrs 1.3 Gyrs
Endosymbiosis Prokayote Bacteria Bacteria: Future Mitochondria Primitive Eukaryote Nucleus
Cyanobacteria: Synechocystis Euglena
Prokayotes Endosymbiosis Sequence Cyanobacteria Bacteria Primitive Eukaryote Mitochondria Chloroplast Modern Eukaryote Nucleus
Is Giardia aprimative eykaryote? Contains no Mitochondria
Evidence for Endosymbiosis • Evidence • Double Membrane • DNA & Ribosomes (simplified) • Genetic Sequencing Eukaryote Chloroplast Mitochondria Nucleus
Zooxanthellae Endosymbiosis in Action Coral Polyps
Note:Evolution involves MergersSome traits come “Prepackaged”
5. Sexual Reproduction Complete Organism Fertilization (Combination of genes from 2 parents) Meiosis Sperm & Egg Bottom Line: Increase in Genetic Diversity Evolution can occur faster
6. Multi-Celled Organism Colony - Group of cells each functioning as a single organism Multi-Celled Organism - Group of cells that have differentiated to perform different tasks - together make up a single organism
Modern Colony Volvax (algae) Plant’s first then Animals
Multicellular Animal Embryos Doushantuo Formation, China Fossil Embryo from Neoproterozoic
Ediacara Hills, Australia Dickinsonia
Ediacara Fauna Spriggina floundersi