Chapter 26.Origin of Life

The historical tree of life can be documented with evidence…

1. Chemicals - CHONP CH2O – Carbohydrates CHO – Lipids (fat) CHON – Protein (amino acids)

CHONP – Nucleic Acids (Nucleotides: DNA, RNA)

2. Anaerobic Prokaryotes – bacteria that exists w/o O2

3. Photosynthetic prokaryote Cyanobacteria 1st sign of free oxygen

4. Aerobic Prokaryotes

5. Eukaryotes - mitochondria - chloroplasts

Life has changed & changed the Earth

Living creatures have changed Earth’s environment, making other life possible

Abiotic synthesis Testable hypothesis

1920Oparin & Haldane propose reducing atmosphere hypothesis

1953Miller & Urey test the hypothesis

Conditions on early Earth Reducing atmosphere

electron-adding water vapor, CO2, nitrogen, NOx, CH4,

NH3, H2, H2S

Energy source lightning, UV radiation, volcanic

What’smissing from

that atmosphere?!

Stanley Miller

University of Chicago

yieldedamino acids

hydrocarbonsN bases

other organic molecules

Origin of Life hypothesis Abiotic synthesis of organic molecules

amino acids & nucleotides Building polymers

joining molecules (CHONP) into polymers proteins & nucleic acids

Protobionts packaging polymers into membrane-bound

droplets maintain internal chemistry

Origin of self-replicating molecules makes inheritance possible

Protobionts Life reproduction & metabolism

An artificially prepared vesicle composed of a bilipid layer.Is being used in medicine to deliver drugs, i.e. for some cancer treatment

Believed to be evolutionary precursors to prokaryotic cells

RNA world RNA is likely first genetic material

multi-functional molecule codes information enzyme functions

ribozymes replication

regulatory molecule transport molecule

Dawn of natural selection

Key Events in Origin of Life Key events in

evolutionary history of life on Earth life originated

3.5–4.0 bya

Prokaryotes Prokaryotes dominated life

on Earth from 3.5–2.0 bya

3.5 billion year old fossil of bacteria modern bacteria

Stromatolitesfossilized mats of prokaryotes resemble modern microbial colonies

Lynn Margulis

Oxygen atmosphere Oxygen begins to accumulate 2.7 bya

photosynthetic bacteria cyanobacteria (blue-green algae)

reducing oxidizing atmosphere corrosive

banded iron in rocks = rusting

Endosymbiosis Evolution of eukaryotes

membrane bound organelles = 2.1 bya

Cambrian explosion 543 mya

within 10–20 million years most of the major phyla of animals appear in fossil record

The Chicxulub impact crater in the Caribbean Sea near the Yucatan Peninsula of Mexico indicates an asteroid or comet struck the earth and changed conditions 65 million years ago

Diversity of life & periods of mass extinction

Note the suspected causes of the Mass Extinctions

Five Major Extinctions – periods of Punctuated Equilibrium:

* Not responsible for names/dates *

• 440 mya Ordovician-Silurian extinction – massive glaciations that locked up much of the world's water as ice and caused sea levels to drop precipitously. The event took its hardest toll on marine organisms such as shelled brachiopods, eel-like conodonts, and the trilobites.

• 360 mya Devonian extinction a drawn-out event eliminated about 70 percent of all marine species from Earth over a span of perhaps 20 million years. Suspect impact, decreased oxygen in oceans, and global cooling. Pulses, each lasting 100,000 to 300,000 years, are noted.

• 250 mya Permian-Triassic extinction beliefs of asteroid or comet, but, again, no crater has been found. Another strong contender is flood volcanism in Russia, or impact-triggered volcanism. Whatever it was, proved to be the deadliest: More than 90 percent of all species perished.

• 200 mya Triassic-Jurassic extinction coincided with massive lava eruptions in central Atlantic. Asteroid impact is also suspected but no telltale crater identified. About 20 percent of all marine families went extinct, as well as most mammal-like creatures, many large amphibians, and all non-dinosaur archosaurs.

• 65 mya Cretaceous extinction - an extraterrestrial impact off Mexico's Yucatán Peninsula and global warming fueled by volcanic eruptions at the Deccan Flats in India coincided with the extinction of dinosaurs, as well as about half of all species on the planet

Stop here

Early mammal evolution 125 mya mammals

began to radiateout & fill niches

Classification Linnaeus used structural similarity 1969

Robert Whittaker devised 5 Kingdom system Monera Protista Plantae Fungi Animalia

Re-Classifying Life New groupings

molecular data challenges 5 Kingdoms Monera is too diverse

2 distinct lineages of prokaryotes Protists are too diverse

3 Domain system Super Kingdoms

Bacteria Archaea

extremophiles = live in extreme environments Eukarya

eukaryotes

Bacteria Archae-bacteria

AnimaliaFungiProtista Plantae

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Formation of earth

Molten- hot surface ofearth becomes somewhatcooler

Oldest definite fossilsof prokaryotes

Appearance of oxygenin atmosphere

Oldest definite fossilsof eukaryotes

First multicellularorganisms

Appearance of animalsand land plants

Colonization of landby animalsPaleozoic

Mesozoic

Cenozoic

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KingdomProtista

KingdomFungi

KingdomPlantae

KingdomAnimalia

KingdomArchaebacteria

KingdomBacteria