Origin and Evolution of Life on Earth Bennett & Shostak Chapter 6Origin and Evolution of Life on Earth – Chapter 6 OverviewSearching for the originPanspermiaScience Searching for the OriginSearching for the Origin: Where on Earth?Searching for the OriginSearching for the Origin: Comparative GenomicsSearching for the Origin: Three Branches of Life FormsSlide 10Life and AtmosphereBeginnings of Life on EarthThe Citric Acid CycleiClicker QuestionSlide 15Slide 16Slide 17Miller-Urey ExperimentSlide 19Significance of and Sequel to Urey Miller ExperimentChemical BeginningsSlide 22Slide 23Evolutionary Perspective of EnzymesRibozymesRibozymes (continued)Summary of RibozymesRNA WorldFunctional Beginnings of Life: Transition from Chemistry to BiologyChemical EvolutionSlide 31Slide 32Slide 33Ocean Edge ScenarioSlide 35ProkaryotesSlide 37Prokaryotes and Atmospheric OxygenProkaryotes and OxygenSlide 40Slide 41Slide 42Slide 43Slide 44Slide 45Eukaryotes and an Explosion of DiversityEukaryotes and explosion of diversityFirst Eukaryotic CellsSlide 49Mitochondria and ChloroplastsSexual Reproduction and MulticellularityMass Extinctions, Asteroids and Climate ChangeMass Extinctions, Asteroids and Climate Change: K-T BoundaryMass Extinctions, Asteroids and Climate Change: Other examplesSlide 55Slide 56Evolutions of HumansArtificial LifeSlide 59Slide 60Origin and Evolution of Life on Earth: Conclusions1Origin and Evolution ofLife on EarthBennett & Shostak Chapter 6HNRS 228 Astrobiologyw/Dr. H. Geller2Origin and Evolution of Life on Earth – Chapter 6 Overview•Searching for the origin (6.1)•Functional beginnings of life (6.2)–From chemistry to biology at the molecular level•Prokaryotes and oxygen (6.3)•Eukaryotes and explosion of diversity (6.3)•Mass extinctions, asteroids and climate change (6.4)•Evolutions of humans (6.5)•Science in Action: Artificial Life (6.6)3Searching for the origin•Origin of Life Theories–Special Creation•Oldest and most widely accepted hypothesis.–Extraterrestrial Origin•Panspermia - Cosmic material may have carried complex organic molecules to earth.–Spontaneous Origin•Life evolved from inanimate matter.4Panspermia5Science Searching for the Origin•Tools and methodologies–Principles of physics (e.g., 1st and 2nd Law of TD)–Principles of geology (e.g., relative/absolute dating)–Principles of chemistry (e.g., chemistry of water)–Principles of biology (e.g., key macromolecules)–Occam’s razor where appropriate•Conclusions: plausible scenario of the events and processes that lead to the origin of life6Searching for the Origin: Where on Earth?•Options–Continental landscapes–Shallow pools–Hot springs–Deep sea vents–Deep in crust–Under frozen seas•Data to support one or the other–Comparative genomics–Chemical energy (hydrogen sulfide)FeS + H2S FeS2 + H2 + Free Energy•Conclusion: deep sea vents–Probability of bombardment7Searching for the Origin•When did life begin?•Evidence–Widespread life forms (3.5 B years ago)–Stromatolites (3.5 B years ago)–Fossilized cells (3.5 B years ago)–Radiometric dating: carbon isotopes (3.85 B years ago)•Carbon 12 versus Carbon 13•Range of dates: 4.1 to 3.85 B years ago•Conclusions–Life arose late in the Hadean Eon–Life colonized planet in very short time frame (< 500 M years)8Searching for the Origin: Comparative Genomics•Comparative morphology versus comparative genomics•“Living Fossils” of DNA and RNA–Sequence of nucleotides in DNA and genome–Pattern and process of change in sequences–Comparing sequences reveals a pattern/order•Methodology of comparison – rRNA (ribosomal RNA)9Searching for the Origin: Three Branches of Life Forms•Results from comparative genomics–Three major domains•Bacteria•Archaea•Eukarya•Common ancestor analysis•Comparison to organisms today–Deep sea volcanic vents–Thermophiles (hyperthermophiles)–Comparison to environment of Hadean Eon10Searching for the OriginDomain Domain DomainBacteria Archaea Eukarya Common Ancestor11Life and Atmosphere•One assumption about the early atmosphere was a reducing atmosphere of carbon dioxide, nitrogen gas, and water vapor, but very little oxygen.–Amino acids would therefore not last long.•Atmosphere would have changed with the advent of photosynthesis.12Beginnings of Life on Earth•Organic chemistry*•Transition from chemistry to biology•Panspermia•The evolution of sophisticated features of metabolism and information brokers•Conclusions_________* Enzymes first or TCA or ?13The Citric Acid Cycle14iClicker Question•The origin of life on Earth most likely occurred–A before 4.5 billion years ago–B between about 4.5 billion years ago and 3.5 billion years ago–C between about 3.0 billion years ago and 2.5 billion years ago–D between about 2.5 billion years ago and 2.0 billion years ago15iClicker Question•The origin of life on Earth most likely occurred–A before 4.5 billion years ago–B between about 4.5 billion years ago and 3.5 billion years ago–C between about 3.0 billion years ago and 2.5 billion years ago–D between about 2.5 billion years ago and 2.0 billion years ago16iClicker Question•The first living organisms probably were–A cells without nuclei that used RNA as their genetic material–B cells with nuclei that used RNA as their genetic material–C cells with nuclei that used DNA as their genetic material17iClicker Question•The first living organisms probably were–A cells without nuclei that used RNA as their genetic material–B cells with nuclei that used RNA as their genetic material–C cells with nuclei that used DNA as their genetic material18Miller-Urey Experiment•Stanley Miller and Harold Urey (1953) attempted to reproduce conditions at the ocean’s edge under a reducing atmosphere.–Were able to form amino acids with the addition of lightning to a reducing atmosphere rich in hydrogen and devoid of oxygen.1920Significance of and Sequel to Urey Miller Experiment•Multiple variations of the study (e.g., atmosphere)–20+ amino acids, sugars, bases for DNA and RNA, ATP, etc.•Significance: scenario for the abiotic formation of key carbon polymers (macromolecules)•Probable environments –Deep sea vents–Tidal pools (role of repeated evaporation and concentration – “evapoconcentration”; asteroid bombardment)•Chemical