Life in the Precambrian Prelude to Us

Major Steps in the Precambrian Evolution of Life 1.Origin of Life ( Gyrs) 2.Photosynthesis ( Gyrs) 3.Aerobic (Oxygen-based) Respiration (3-2 Gyrs) 4.Eukaryotes / Endosymbiosis ( Gyrs) 5.Sex / Death ( Gyrs) 6.Multicellular Life (1, Myrs) 7.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 Much More Difficult Nucleotides Warm Pond or Hydrothermal Vents

“Primordial Soup”

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 Proteins help make DNA RNA codes to make first proteins

Membrane Lipids tend to stick together

Metabolism Heterotrophic (consummers) / Fermentation Why? 1.Simple process (Need to eat before you learn to cook) 2.Present in all organisms 3.Doesn’t require a cell membrane More details to come…

LUCA: Last Universal Common Ancestor

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)

12 C/ 13 C Enrichment in Organics 7‰ 12 C Depleted (less 12 C than atm) 18‰ 12 C Enriched (more 12 C than atm) 25±10‰ 12 C Difference CO 2 in Atmosphere (includes 12 CO 2 and 13 CO 2 )

Fossil Enrichment

Oldest Fossils: Apex Chert, Australia (3.5 Gyr)

Apex Chert Fossils (3.5 Gyr)

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 GlucoseEnergy Glucose Energy Glucose Synthesis 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

Formed Colonies called Stromatolites

Stromatolites Mats of Cyanobacteria

Modern Stromatolites: Shark Bay, Australia

North Pole, Australia Stromatolite (3.5 Gyrs) Existed on Earth for over 3.5 Gyrs!

3. Aerobic Respiration Back to Metabolism… Oxygen Gas Warfare - Oxygen is lethal to most existing bacteria = Advantage - removes competition

Aerobic Respiration Burning 1 glucose molecule in the presence of oxygen releases 36 energy units! Three step process - each a modification of earlier form of metabolism However: (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 Fermentation (Anaerobic Respiration) Glucose Synthesis Anaerobic Photosynthesis Aerobic Photosynthesis Aerobic Respiration 3.8 Gyrs 2.5 Gyrs

4. Eukaryotes & Endosymbiosis Chuaria circularis 800 Myrs Tawuia dalensis Fossil Acritarch First Appear 1.6 Gyrs

Oldest Eukaryote Grypania spiralis 1.3 Gyrs 2.1 Gyrs

Endosymbiosis Bacteria: Future Mitochondria Nucleus Bacteria Primitive Eukaryote Prokayote

Euglena Cyanobacteria: Synechocystis

Endosymbiosis Sequence Nucleus Mitochondria Chloroplast Cyanobacteria Bacteria Primitive Eukaryote Modern Eukaryote Prokayotes

Is Giardia a primative eykaryote? Contains no Mitochondria

Evidence for Endosymbiosis Mitochondria Chloroplast Eukaryote Nucleus Evidence Double Membrane DNA & Ribosomes (simplified) Genetic Sequencing

Endosymbiosis in Action Coral Polyps Zooxanthellae

Note: Evolution involves Mergers Some traits come “Prepackaged”

5. Sexual Reproduction Bottom Line: Increase in Genetic Diversity Evolution can occur faster Meiosis Sperm & Egg Fertilization (Combination of genes from 2 parents) Complete Organism

The Price of Sex: With Sex comes “True Genetic Death”

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

Late Precambrian Trace Fossils

7. Skeletons and Shells Small Shelly Fossils (SSF’s)

Cambrian Explosion

Life on Earth - Timing Single Celled Life OnlyNo Life Multi-Celled 4.6 ByrsToday First Eukaryotes Oxygen Revolution Aerobic Respiration First Photosynthesis & Stromatolites First Sex