Chapter 26. Origin of Life

The historical tree of life can be documented with evidence… 1. Chemicals - CHONP CH 2 O – Carbohydrates CHO – Lipids (fat) CHON – Protein (amino acids) CHONP – Nucleic Acids (Nucleotides: DNA, RNA) 2. Anaerobic Prokaryotes – bacteria that exists w/o O 2 3. Photosynthetic prokaryote Cyanobacteria 1 st 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  1920 Oparin & Haldane propose reducing atmosphere hypothesis  1953 Miller & Urey test the hypothesis

Conditions on early Earth  Reducing atmosphere  electron-adding  water vapor, CO 2, nitrogen, NO x, CH 4, NH 3, H 2, H 2 S  Energy source  lightning, UV radiation, volcanic What ’ s missing from that atmosphere?!

Stanley Miller University of Chicago yielded amino acids hydrocarbons N 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

Stromatolites fossilized 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 radiate out & 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

BacteriaArchae- bacteria AnimaliaFungiProtistaPlantae Formation of earth Molten- hot surface of earth becomes somewhat cooler Oldest definite fossils of prokaryotes Appearance of oxygen in atmosphere Oldest definite fossils of eukaryotes First multicellular organisms Appearance of animals and land plants Colonization of land by animals Paleozoic Mesozoic Cenozoic Millions of years ago ARCHEAN PRECAMBRIAN PROTEROZOIC PHANEROZOC

Kingdom Protista Kingdom Fungi Kingdom Plantae Kingdom Animalia Kingdom Archaebacteria Kingdom Bacteria