CH 26: Early Earth and the CH 26: Early Earth and the Origin of LifeOrigin of Life

Presentation by Alisa Gordon, Presentation by Alisa Gordon, Erica Guo, and Victoria ChenErica Guo, and Victoria Chen

The History of Life: An IntroductionThe History of Life: An Introduction

Earth was formed about 4.5 billion years Earth was formed about 4.5 billion years agoago

Life is thought to have formed between 3.5 Life is thought to have formed between 3.5 and 4 billion years agoand 4 billion years ago

Evidence? Isotopes in carbon found in 3.8 Evidence? Isotopes in carbon found in 3.8 billion year old rocks in Greenlandbillion year old rocks in Greenland

What was the first life?What was the first life?

Prokaryotes were probably the first Prokaryotes were probably the first organismsorganisms

Evidence through Evidence through StromatolitesStromatolites, banded , banded domes of sedimentary rock domes of sedimentary rock

Stromatolites are similar layered mats in salt Stromatolites are similar layered mats in salt marshes formed today by colonies of bacteria.marshes formed today by colonies of bacteria.

Oldest known fossils of Living organisms Oldest known fossils of Living organisms are found in 3.5 billion year old are found in 3.5 billion year old Stromatolites in Western AustraliaStromatolites in Western Australia

Stromatolite Stromatolite

The History of lifeThe History of life

1.1. After the Earth’s crust cooled and solidified, After the Earth’s crust cooled and solidified, we believe that prokaryotes were the first to we believe that prokaryotes were the first to originateoriginate

2.2. Bacteria and Archaea became the two best Bacteria and Archaea became the two best thriving prokaryotes (their split happened 3 thriving prokaryotes (their split happened 3 billion years ago)billion years ago)

3.3. Evolution of aerobic life began 2.5 billion Evolution of aerobic life began 2.5 billion years ago, thanks to the presence of O2 from years ago, thanks to the presence of O2 from

early photosynthetic prokaryotesearly photosynthetic prokaryotes

History of Life (continued)History of Life (continued)

4.4. Oldest Eukaryotic fossils = 1.7 billion Oldest Eukaryotic fossils = 1.7 billion years ago, but evolved hundreds of years ago, but evolved hundreds of millions of years before handmillions of years before hand

-evidence that they evolved from symbiotic -evidence that they evolved from symbiotic communities of prokaryotescommunities of prokaryotes

5.5. ProtistsProtists: large group of unicellular : large group of unicellular organismsorganisms

- Plants, animals, and fungi arose from - Plants, animals, and fungi arose from distinct protists distinct protists

Where they came fromWhere they came from

History of Life( continued)History of Life( continued)

6.6. Oldest animal fossils = 700 million years Oldest animal fossils = 700 million years ago from (specifically, the Precambrian ago from (specifically, the Precambrian Era)Era)

- Fauna not too diverse- Fauna not too diverse

7.7. For 3.5 billion years, life was confined to For 3.5 billion years, life was confined to aquatic environment (90% of its aquatic environment (90% of its existence)existence)

The Origin of LifeThe Origin of Life

The first cells may have originated by The first cells may have originated by chemical evolution on a young Earthchemical evolution on a young Earth

Life on Earth developed from nonliving Life on Earth developed from nonliving materialsmaterials

Lightning, volcanic activity, meteorite Lightning, volcanic activity, meteorite bombardment, ultraviolet radiationbombardment, ultraviolet radiation

Created environment in which early stages of Created environment in which early stages of biological inception was inevitablebiological inception was inevitable

How did they evolve?How did they evolve?

One Hypothesis:One Hypothesis:Abiotic synthesis and accumulation of small Abiotic synthesis and accumulation of small organic moleculesorganic molecules

Joining of molecules to polymers: proteins, Joining of molecules to polymers: proteins, nucleic acidsnucleic acids

Aggregation of molecules into droplets: Aggregation of molecules into droplets: ProtobiontsProtobionts

Origin of heredityOrigin of heredity

Abiotic synthesis of organic Abiotic synthesis of organic monomers monomers

1920 – A. I. Oparin and J. B. S. Haldane 1920 – A. I. Oparin and J. B. S. Haldane Conditions on primitive Earth favored creation Conditions on primitive Earth favored creation of organic compoundsof organic compounds

Primitive Earth’s atmosphere had less Primitive Earth’s atmosphere had less oxidizing atmosphereoxidizing atmosphere

Making organic molecules was facilitated by Making organic molecules was facilitated by intense UV radiation – the earth had a primitive intense UV radiation – the earth had a primitive atmosphereatmosphere

Abiotic synthesis of organic Abiotic synthesis of organic monomers monomers

1953 – Stanley Miller and Harold Urey1953 – Stanley Miller and Harold UreyTested Oparin-Haldane hypothesisTested Oparin-Haldane hypothesis

Included variety of amino acids and other organic Included variety of amino acids and other organic compounds in living organismscompounds in living organisms

Apparatus used to simulate chemical dynamics on Apparatus used to simulate chemical dynamics on primitive Earthprimitive Earth

Laboratory analogs have produced 20 amino acids found in Laboratory analogs have produced 20 amino acids found in organismsorganisms

Many doubt atmosphere was reason for Many doubt atmosphere was reason for development, believe that submerged volcanoes development, believe that submerged volcanoes and deep-sea vents provided the resources and deep-sea vents provided the resources neededneeded

Laboratory StimulationsLaboratory StimulationsAbiotic synthesis of complex organic molecules Abiotic synthesis of complex organic molecules was bound to happen:was bound to happen:

Smaller organic polymers (like proteins) had to joinSmaller organic polymers (like proteins) had to join

No enzymes to catalyze a cell’s reaction, and water No enzymes to catalyze a cell’s reaction, and water dissolves polymers…So how did they?dissolves polymers…So how did they?

Answer- Polymerization occurs when dilute Answer- Polymerization occurs when dilute solutions of organic monomers dripped onto hot solutions of organic monomers dripped onto hot sand, clay or rocksand, clay or rock

Using this polymerization method, we can make Using this polymerization method, we can make proteinoids, proteinoids, polypeptides produced by abiotic polypeptides produced by abiotic synthesissynthesis..

SubstratesSubstrates

Clay is important substrate for the Clay is important substrate for the polymerization reactions steps to lifepolymerization reactions steps to life

Concentrates amino acids and other organic Concentrates amino acids and other organic molecules and binds them with the clay molecules and binds them with the clay particlesparticles

Iron and zinc function like catalystsIron and zinc function like catalysts

Alternative to clay: Iron pyrite (Fools gold)Alternative to clay: Iron pyrite (Fools gold)Hypothesized to be a substrate by Gunter Hypothesized to be a substrate by Gunter Wachterhauser Wachterhauser

ExamplesExamples

ProtobiontsProtobionts

Protobionts: aggregates of abiotically Protobionts: aggregates of abiotically produced moleculesproduced molecules

Not capable of reproduction, but have Not capable of reproduction, but have metabolism and excitabilitymetabolism and excitability

Have different internal chemical balance then Have different internal chemical balance then its environmentits environment

CoacervatesCoacervates are droplets that reassemble are droplets that reassemble themselves when macromolecules shakenthemselves when macromolecules shaken

CoacervatesCoacervates

More on ProtobiontsMore on Protobionts

Form spontaneously from abiotically Form spontaneously from abiotically produced organic compoundsproduced organic compoundsHave protein membrane that swell or Have protein membrane that swell or shrink in different salt concentrationsshrink in different salt concentrationsDischarge voltage like nerve cellsDischarge voltage like nerve cellsProtobionts that formed long ago though Protobionts that formed long ago though would not have had refined enzymes, would not have had refined enzymes, which meant they had no inherited which meant they had no inherited instructioninstruction