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The Tree of Life Changing life on a changing earth Interactions between organisms and their environment • Geologic changes – Isolation • Environment influences organisms – Natural selection • Organisms influence environment – Recycling of nutrients – Evolution of oxygen Conditions on the Early Earth • ~4.6 billion years old • ~3.9 bya- Cooled enough for solid rock to form • Early atmosphere= reducing (adds electrons) – No oxygen – Water vapor – CO, NO, CO2, methane, hydrogen 4 events that led to life on earth • • • • Synthesis of small organic molecules Joining monomers into polymers Packaging of polymers into protobionts Self replicating molecules made inheritance possible Miller and Urey Origin of organic molecules • Extraterrestrial origin? – Chondrite containing 80 amino acids, small contribution • Reducing environments? – Smoke vents – Thermal pools Polymers • Abiotic synthesis – Hot rocks, amino acids – Act as catalysts for the formation of other macromolecules The first life • 2 properties of life – Accurate replication – Metabolism • Neither can exist independently – DNA requires enzymes and energy to copy – Metabolism requires DNA to produce enzymes Protobionts • Membranes full of macromolecules • Qualities of living things – Simple reproduction – Metabolism – Different chemical makeup than environment Primitive metabolism • Liposomes – Osmotic shrink and swell – Incorporate membrane channels – Discharge voltage RNA World • Ribozyme- RNA that acts as an enzyme – Copy RNA – Modify other strands of RNA – Act as enzymes • Natural selection acts on RNA • Environment acts on protobionts The Fossil Record • Earliest stages aren’t recorded • Some species are over represented • Not 100% accurate, but pretty good Geologic Record Geologic eras are marked by mass extinctions and prevalent species Mass Extinctions • Environmental change – Ice age, warming – Changes in solar energy – Atmospheric composition • Species interactions increase extinctions • 80-90% of all species went extinct Prokaryotic evolution • Earliest prokaryotes appeared 3.5 billion years ago • Stromatolites • Autotrophic – Made all the macromolecules they needed Prokaryotes changed their environment • Photosynthesis produced elemental oxygen as a byproduct from splitting water • Oxygen is a strong oxidizing agent, toxic to many anaerobes • Eventually produced ozone layer Eukaryotic Cells • Oldest eukaryotic fossils are ~2.1 billion years old • Have found cholesterol in 2.7 billion year old rocks, suggests that eukaryotes are older Endosymbiosis Multi-cellularity • First multi cellular organisms appeared ~1.5 billion years ago • Started as colonial protists – Autonomous replication – Specialized function • Filamentous algae Cambrian Explosion • Multicellularity allows greater diversity • Most phyla of animals appeared during the beginning of the Cambrian period (~1billion years ago) Colonization of land • Provided increased habitats • Adaptations to prevent dehydration – Exoskeleton – Cuticle – Root systems Continental drift • Biogeography • Fossil record
