Chapter 26 ~ Early Earth and The Origin of Life

Early history of life

Solar system~ 12 billion years ago (bya)

Earth~ 4.5 bya Life~ 3.5 to 4.0 bya Prokaryotes~ 3.5 to 2.0 bya

stromatolites Oxygen accumulation~ 2.7 bya

photosynthetic cyanobacteria Eukaryotic life~ 2.1 bya Muticelluar eukaryotes~ 1.2 bya Animal diversity~ 543 mya Land colonization~ 500 mya

Stromatolites

Little bit of history:

Antoni van Leeuwenhoek- animalcules (1675)

Spontaneous generation- John Needham (1750)

Biogenesis- Lazzaro Spallanzani(1767), Rudolf Virchow(1858) and Luis Pasteur (1861)

The Origin of Life Spontaneous generation vs. biogenesis

Needham vs. Pasteur

The Origin of Life The 4-stage Origin of life Hypothesis: 1- Abiotic synthesis of organic monomers 2- Monomers into Polymers 3- Molecule packaging (“protobionts”) 4- Origin of Self-replicating molecules

Organic monomers/polymer synthesis

Oparin (Rus.)/Haldane (G.B.): 1920 Hypothesis: primitive earth atmosphere

allowed inorganic precursors to synthesize organic compounds (abiotic process)

reducing atmosphere from volcanic vapors with lightning & UV radiation enhances complex molecule formation (no O2)

Oceans were a solution of organic molecules or “primitive soup” from which life arose

Organic monomers/polymer synthesis Miller/Urey experiment(1953): Tested Oparin and Haldane’s

hypothesis Hydrogen (H2), methane (CH4),

ammonia(NH3), represented early atmosphere

Water represented early seas Electrodes simulated lightning Condenser cooled gases to simulate rain

Millers results:

periodically collection and analyzing samples: the following was found-

Oily hydrocarbons Variety of amino acids Nitrogen bases ATP

Organic monomers/polymer synthesis

Other scientist discovered abiotic polypeptides or proteinoids

Formed from dripping organic monomers on hot sand, clay or rock.

Organic monomers/polymer synthesis (More abiotic synthesis of organic

compounds) Coacervates = tiny, spherical

droplets of organic molecules (proteins, carbs, lipids) formed via hydrophobic forces– Proposed by Oparin in his version of

the biogenesis theory

coacervates

Today: -Miller and Urey = debate - many scientist believe that atmosphere did

not play a significant role in the abiotic formation of organic compounds

Submerged volcanoes and hot deep sea vents probably provided early resources

Exampe: Inorganic sources of sulfur and iron could have been used to produce energy(ATP)

Other sources for organic compounds:

Nitrogen bases such as Adenine have been formed from cyanide reactions in the clouds of dust between stars

Meteorites carry the organic materials to earth

Abiotic genetic replication

What was the first genetic material?– DNA or RNA?

Scientists are making a case for RNA

Evidence for RNA as first genetic material:

1. Ribozymes: – RNA catalysts– Can make complementary copies of short

pieces of RNA – Self splicing– Can excise pieces of different molecules– autocatalytic

Evidence for RNA as first genetic material:

2. Laboratory observations of natural selection:– RNA can conform to many different shapes– Can interact with surrounding molecules – Certain base sequences could be more stable

and replicate faster

Abiotic genetic replication

Evidence for RNA as first genetic material:

3. RNA molecules have the capacity to store information– RNA molecules replicate information

– Can assist in the formation of peptides (modern function of RNA in ribosomes)

– RNA could have acted as a template for DNA nucleotides to assemble

– All of this MAY have taken place in protobionts

Evidence of Biological Evolution: 1. Geographical 2. Geological 3. Physical 4. Chemical 5. Mathematical Applications 6. Molecular 7. Morphological 8. Genetic

How is early life on Earth chronicled?

Radiometric dating:– Carbon-14 (good for 50,000 years)– Potassium-40

Magnetic dating: alignment of iron particles frozen in ancient rock with the earth’s magnetic field– Magnetic reversals

Thermoluminescence: heating electrons, measuring and analyzing the light emitted.

Morphological Evidence:

Morphological homologies:– Embryology– Vestigial structures

Biochemical and genetic evidence:

mtDNA: Y-chromosome DNA sequencing

Mathematical Models:

Graphical analysis of allele frequencies– BLAST

Phylogenic trees Sequencing data

Geological Record:

1. Archeaen Eon 2. Proterozoic Eon 3. Phanerozic Eon

Evidence of evolution within changing environments:

Speciation and Extinction Five major mass extinctions Human impact

Mass Extinctions:

Two Mass Extinctions have received the most attention:

–Permian

–Cretaceous

Permian Mass Extinction:

Permian period- defines the boundary between the Mesozoic and Paleozoic eras.

251 million years ago 96% of aquatic life went extinct (and some

terrestrial life) Occurred in less than 5 million years Volcanic eruptions in Siberia

Cretaceous Mass Extinction:

Cretaceous period marks the boundary between Mesozoic and Cenozoic eras.

65 million years ago Killed more than half of the aquatic life Exterminated many families of terrestrial

plants and animals Most if not all Dinosaurs

Cretaceous continued:

Large comet(10km)collided with the Earth: Evidence:

– Crater at the Yucatan Penninsula (chicxulub crater- 180 km in diameter)

– Thin layer of clay enriched Iridium that separates the Mesozoic from the Cenozoic eras

– Caused a spike in volcanic activity

Prokaryotic Exploitation:

Stromatolites– Oldest known fossils- 3.5 billion years– Layers of bacteria and sediment

Autotrophs and Heterotrophs: – Evolved from protobionts– Only life forms on earth for 1.5 billion years– Nonoxygenic photosynthesis- chemisomotic

synthesis of ATP.

Photosynthesis and Oxygen Revolution:

Enter cyanobacteria– Saturated oceans with oxygen– Formation of oxides (FeO)

• Accumulates as sediments

• Compressed into rock

– Oxygen gas bubbles out of oceans into atmosphere

• Atmosphere goes from reducing to oxidizing.

Genesis of Eukaryotes:

Oldest Eukaryotic Fossils: 2.1 billion years ago??

Endosymbiosis- hypothesis that explains how large complex eukaryotes evolved from smaller prokaryotic cells. – Undigested prey– Parasites

• Eventually became mutually benefitial

What came first?

Mitochondria or the Chloroplast??

Genetic Chimeras:

Composed of different populations of genetically different cells. – Mitochondria, chloroplasts and nuclear

genomes come from different forms of bacteria.

Genetic Annealing:

Gene transfer between many different bacterial lineages– Eukaryotic cells may be a product of this

process.

Multicellularity:

Oldest multicellular organisms = 1.5 – 1.2 billion years ago. – Limited to size because of ice age

• Between 750 - 570

The Colonial Connection:

Multicellular organisms lived in colonies.– Autonomous– Self replicating– differentiating

The Cambrian Explosion:

First 20 million years of the Cambrian period most of the major phyla of animals suddenly appear– About 1 billion to 700 million years ago– Animals with exoskeletons and hard shells

Colonization of land:

500 million years ago Macroscopic life:

– Plants– Fungi– Animals

What are some major problems that terrestrial organisms had to over come?

Continental Drift:

Pangea Spatial distribution of life

– Reshapes biological diversity Mesozoic- continents start to drift

– Created separate zones of evolution with different lineages of plants and animals

Taxonomy:

Linnaeus:

– First classification system

– Divided all forms of life into two categories

– Plants and Animals

Robert H. Whittaker: Cornell University Created five kingdom system of

classification Monera (bacteria- prokaryotic cells) Protista- single celled eukaryotes Fungi – multicellular eukaryotes Plants- multicellular eukaryotes Animals- multicellular eukaryotes

Three Domain System:

Three Super Kingdoms:– Bacteria– Archaea– Eukarya

Universal Ancestor: Four Characteristics:

– The cell was surrounded by a lipid cellular membrane

– Genetic code based on DNA

– The genetic code was expressed with single stranded RNA intermediates

– The cell multiplied and duplicated all of its contents, followed by cell division

The Major Lineages of Life