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Chapter 25

Chapter 25. The History of Life on Earth. The History of Life on Earth. Macroevolution - the pattern of evolution over large time scales. Earliest evidence of life: 3.5 byo fossils How did the first living cells appear? Abiotic synthesis of small organic molecules

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Chapter 25

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  1. Chapter 25 The History of Life on Earth

  2. The History of Life on Earth • Macroevolution- the pattern of evolution over large time scales. • Earliest evidence of life: 3.5 byo fossils • How did the first living cells appear? • Abiotic synthesis of small organic molecules • Joining of these molecules into macromolecules • Packaging of these molecules into protobionts • Origin of self-replicating molecules that made inheritance possible

  3. Synthesis of Early Earth • Formed about 4.6 billion years ago • Oparin and Haldane- primordial soup • Miller and Urey- tested Oparin and Haldane hypothesis in lab- produced multiple amino acids and other organic compounds • Protobionts- collections of abiotically produced molecules surrounded by a membrane-like structure

  4. Fossil Record • Absolute Dating • Radiometric Dating- based on the decay of radioactive isotopes • Half-Life- the time required for 50% of the parent isotope to decay. • Challenges • Organisms do not use radioisotopes that have long half-lives. • Sedimentary rocks have compounds of different ages.

  5. The Geologic Record • Geologic Record- divided into three eons • Archaean • Proterozoic • Phanerozoic- the last half billion years- divided into three eras • Paleozoic • Mesozoic • Cenozoic Together lasted approx. 4 billion years

  6. First Organisms • Stromatolites- layered rocks that form when certain prokaryotes bind thin films of sediment together. • Endosymbiosis- mitochondria and plastids took residence inside a prokaryote to form a eukaryote • Evidence • Mitochondria and chloroplasts have own DNA • Ribosomes • Mitochondria and chloroplasts replicate independently

  7. Cambrian Explosion- many phyla of living animals appear suddenly in fossils formed early in the Cambrian period (535-525 mya) • Continental Drift- the movement of Earth’s plates, over time. • Supercontinent- formed three times

  8. Mass Extinction- large number of species become extinct throughout Earth. • Consequences: disrupt a thriving ecological community, disappearance of evolutionary lineage

  9. Evolution is like tinkering- a process in which new forms arise by the slight modification of existing forms. Even large changes, like the ones that produced the first mammals, can result from the gradual modification of existing structures or the slight modification of existing developmental genes. • Francois Jacob (modified)

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