The History of Life on Earth

History of Life Originated billion years ago Fossil evidence: stromatolites

Major Episodes in the History of Life Prokaryotes-3.6 billion years ago Prokaryotes diverged into Bacteria and Archaea 2-3 billion years ago Photosynthetic bacteria began producing O billion years ago Eukaryotes emerged 2 billion years ago

Prebiotic Chemical Evolution Abiotic synthesis and accumulation of monomers Formation of polymers Formations of protobionts Origin of heredity during or before protobiont appearance

Protobionts Aggregates of abiotically produced molecules Maintain internal environment, different from surroundings Exhibit some life properties-irritability and metabolism Self-assemble Microspheres and liposomes

Laboratory versions of protobionts

RNA was probably the First Genetic Material If DNA, a primer would be necessary RNA can self-replicate RNA is autocatalytic Achieves unique tertiary structure (different phenotypes)-diversity!

Abiotic Replication of RNA

Hereditary Material Enabled Darwinian Evolution If Protobionts: 1.Incorporated genetic information 2.Selectively accumulated monomers 3.Used enzymes programmed by genes to make polymers 4.Grew and split Then: Variations would lead to natural selection Refinements would have accumulated Lead to the appearance of DNA

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The Fossil Record and Geologic Time Role of sedimentary rocks Fossil dating, use of strata location vs. absolute dating Fossil record incomplete, favors species that existed for a long time, why? Role of continental drift Mass extinctions and adaptive radiations

Key Events in Life’s History Photosynthesis-oxygen revolution-2.7 billion years ago (photosynthetic bacteria) First eukaryotes-2.1 billion years ago, result of endosymbiosis Origin of multicellularity-1.5 billion years ago Cambrian Explosion million years ago first predators, first hard bodied organisms, Cnidaria, Porifera, and Mollusks, bilateral symmetry Colonization of land-began with cyanobacteria 1 billion years ago, necessary adaptations?

Genesis of Eukaryotes: Serial Endosymbiosis? Membrane-bound nucleus Mitochondria, chloroplasts, and the endomembrane system Cytoskeleton flagella Multiple chromosomes Mitosis, meiosis, and sex

The Origin of Eukaryotes?

Secondary Endosymbiosis

Continental Drift Pangea: supercontinent, broke apart during Mesozoic era. Explains distribution of fossils and extant organisms. (lungfishes, marsupials) Generated by plate tectonics Can result in volcanoes (Krakatau, Tambora), tsunamis.

Examples of Mass Extinctions Approximately 12 mass extinctions Permian extinctions-250 million years ago, 90% species (marine) eliminated Cretaceous extinctions-65 million years ago, 50% marine species, dinosaurs, many plants Asteroid impact (Alvarez or Impact Hypothesis), crater from Cretaceous extinction- 180 km dia. Yucatan coast Role of the Siberian Traps (caused O 2 to drop from 30% to 15% or lower during the Permian period)

Consequences of Mass Extinctions Widespread adaptive radiations Causes?

Mass extinctions

DNA, RNA and Protein Comparisons DNA hybridizations-compare degree of similarity between two species Restriction maps DNA sequence analysis Homologous DNA sequences-mutations accumulate as species diverge Molecular clocks-number of amino acid substitutions is proportional to the elapsed time since divergence

The Origin of Evolutionary Novelty How do novel features that define taxonomic groups above the species level arise? (wings as an example) Gradual refinement of existing adaptations Alternative functions Exaptation: structure that evolved in one context and later was adapted for another function. Examples: feathers, light hollow bones in birds

Genes that control development and evolutionary novelty Sometimes a few changes in the genome causes major changes in the morphology. A system of regulatory genes coordinates activities of structural genes to guide the rate and pattern of development Allometric growth Heterochrony Paedomorphosis Homeosis

Heterochrony-alteration in the time of change in the order of one or more events

Allometric Growth-different body parts grow at different rates. Result: adult is shaped different form the juvenile.

Paedomorphosis: type of heterochrony that describes a condition in which the time of sexual maturity is altered. Retention of ancestral juvenile structures in a sexually mature adult organism

Homeosis-alteration in the placement of different body parts

Hox genes Homeotic genes Responsible for where structures develop on the embryo Responsible for limb formation instead of fin formation