The History of Life on Earth The History of Life on Earth Chapter 25 Chapter 25 Early Earth Earth is about 4 6 billion years old Radiometric dating of meteorites moon rocks Life arose about 3 8 billion years ago No spontaneous generation now but must have happened then Conditions on Early Earth Atmosphere CO2 CH4 NH3 H2S H2O No free oxygen Abundant energy to drive reactions Frequent storms w much lightning Frequent volcanic eruptions Frequent meteor impacts UV light from the sun Testable hypotheses explaining the origin of life 1 Abiotic non living synthesis of small organic molecules 2 Joining these molecules into polymers 3 Packaging these molecules into protobionts precursors to prokaryotic cells Had a surrounding membrane or membrane like structure 4 The origin of self replicating molecules Miller Urey Experiments Electric spark simulates lightning Gases of primeval atmosphere Figure 4 2 Organic molecules amino acids appear after only a few days Abiotic Synthesis of Polymers Small organic molecules polymerize when they are concentrated on hot sand or clay Early Nucleotides Then Earliest cells used RNA to store info Ribozymes to catalyze reactions Possible Sequence Leading to First Prokaryotes self replicating system enclosed in a selectively permeable protective lipid sphere DNA RNA enzymes and other proteins formation of protein RNA systems evolution of DNA formation of lipid spheres spontaneous formation of lipids carbohydrates amino acids proteins nucleotides under abiotic conditions 3 2 1 Concept 25 2 The fossil record documents the history of life Figure 25 4 Fossils Document the History of Life Oldest fossils 3 5 billion years old Sedimentary strata reveal the relative ages of fossils Fossils near surface more recent Deeper fossils more ancient Fossil records shows great changes in organisms through time Dating of Fossils Order of fossils in rock strata tells us the sequence in which they were laid down This only provides relative ages not absolute dates Radiometric Dating Can determine absolute ages of fossils Radioactive isotopes decay into a daughter isotope at a fixed rate life amount of time it takes for 50 of an isotope to decay Figure 25 5 When a certain rock formed it contained 12 mg 40K The rock now contains 3 mg 40K The half life of 40K is 1 3 billion years How old is the rock 1 0 4 BY 2 0 3 BY 3 1 3 BY 4 2 6 BY Carbon 14 decays into Nitrogen 14 and has a life of 5 730 years If you find a fossil with exactly equal amounts of C14 and N14 when did that organism die 1 Recently 2 3 4 5 730 years ago 11 460 years ago 17 190 years ago Concept 25 3 Key events in life s history include the origins of single celled and multi celled organisms and the colonization of land What were the earliest organisms like First organisms were prokaryotes Bacteria Archaea Fed on accumulated organic molecules heterotrophic some were likely autotrophic Oxygenic photosynthetic bacteria evolved 2 7 3 5 billion years ago CO2 H2O Glucose O2 Oxygen begins accumulating in the atmosphere 2 7 billion years ago Figure 25 8 Which is the correct sequence of events 1 2 3 4 anaerobic cells O2 photosynthesis aerobic cells photosynthesis O2 anaerobic cells aerobic metabolism anaerobic cells photosynthesis O2 aerobic metabolism anaerobic cells aerobic metabolism photosyntesis O2 Figure 25 9 The First Eukaryotes Oldest fossils of eukaryotic cells are 2 1 billion years old Endosymbiotic Theory Mitochondria plastids were formerly small prokaryotes living within larger host cells Were possibly undigested prey or internal parasites or mutualists Three lines of evidence that suggests that eukaryotic cells formed symbiotic relationships with bacteria 1 Both chloroplasts and mitochondria contain DNA that is distinct from that found in the nucleus of the eukaryotic cell 2 Similarities in inner membrane structure and functions 3 Both chloroplasts and mitochondria have their own ribosomes and make proteins independent from the cell Clock Analogy Shows time scales involved in the history of life on Earth Figure 26 10 Concept 26 5 Multicellularity evolved several times in eukaryotes The first multi cellular organisms 1 5 1 2 billion years ago Plants primitive marine algae Animals soft bodied marine invertebrates 570 million year old fossil embryos Figure 26 15 The Cambrian Explosion Figure 26 17 542 million years ago Almost all modern forms of animals arose at this time Concept 26 6 New information has revised our understanding of the tree of life Previous Taxonomic Systems Robert Whittaker in Early classification systems had two kingdoms Plants animals 1969 proposed a system with five kingdoms 1 Monera 2 Protista 3 Plantae 4 Fungi 5 Animalia Figure 26 21 Modern Classification System Molecular data has provided new insights regarding the deepest branches of the tree of life Three domain system has replaced the five kingdom system 1 Archaea 2 Bacteria 3 Eukarya
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