Life in the Precambrian

Prelude to Us

Major Steps in the Precambrian Evolution of Life

1. Origin of Life (4.0 - 3.8 Gyrs)

2. Photosynthesis (3.8 - 3.5 Gyrs)

3. Aerobic (Oxygen-based) Respiration (3-2 Gyrs)

4. Eukaryotes / Endosymbiosis (2.1-1.6 Gyrs)

5. Sex / Death (1.2 - 1 Gyrs)

6. Multicellular Life (1,000 - 800 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

MetabolismHeterotrophic (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 SupergroupOldest

Evidence forLife:

IsuaSupergroupGreenland(3.8 Gyrs)

12C/13C Enrichment in Organics

7‰ 12C Depleted(less 12C than atm)

18‰ 12C Enriched (more 12C than atm)

25±10‰ 12C Difference

CO2 in Atmosphere (includes 12CO2 and 13CO2 )

Fossil Enrichment

Oldest Fossils:Apex Chert,

Australia(3.5 Gyr)

ApexChert

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 glucoseNatural selection kicks in

Making Glucose

Fermentation

Glucose Energy

Glucose Energy

Glucose Synthesis

7 of the 11 step are just reverse of Fermentation

Making Glucose with Sunlight

First - Anaerobic PhotosynthesisModified Form of Glucose Synthesis

Hydrogen + Carbon Dioxide --> Glucose

Second - Aerobic PhotosynthesisModified 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

StromatolitesMats 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

Oxygen

Oxygen

Oxygen

Gas Warfare - Oxygen is lethal to most existing bacteria

= Advantage - removes competition

Aerobic Respiration

Burning 1 glucose molecule in the presence of oxygenreleases 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 AcritarchFirst Appear 1.6 Gyrs

Oldest EukaryoteGrypania spiralis

1.3 Gyrs

2.1 Gyrs

Endosymbiosis

Bacteria: Future Mitochondria

Nucleus

Bacteria

Primitive Eukaryote

Prokayote

EuglenaCyanobacteria: Synechocystis

Endosymbiosis Sequence

Nucleus

Mitochondria Chloroplast

Cyanobacteria

Bacteria

Primitive Eukaryote

Modern Eukaryote

Prokayotes

Is Giardia aprimative 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 DiversityEvolution can occur faster

Meiosis

Sperm & Egg

Fertilization(Combination of genes

from 2 parents)

CompleteOrganism

The Price of Sex:

With Sex comes“True Genetic Death”

6. Multi-Celled OrganismColony - 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 firstthen Animals

Multicellular Animal EmbryosDoushantuo Formation, China

Fossil Embryo from Neoproterozoic

Ediacara Hills, Australia

Dickinsonia

Ediacara Fauna

Spriggina floundersi

Late Precambrian Trace Fossils

7. Skeletons and ShellsSmall Shelly Fossils

(SSF’s)

Cambrian Explosion

Life on Earth - Timing

Single Celled Life OnlyNo Life

Multi-Celled

4.6 Byrs Today

First Eukaryotes

Oxygen RevolutionAerobic Respiration

First Photosynthesis & Stromatolites

First Sex