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The History of Life Chapter 17 17-1 The Fossil Record • Fossils are the preserved remains of ancient organisms. • By observing fossils and making comparisons, scientists can determine relationships between ancient organisms – – – – What is the structure of the organism? What did it eat? What ate it? What was the organisms environment like? • By comparing fossils to one another, scientists ordered organisms according to when they lived (The Fossil Record) Fossil Record Continued • The fossil record reveals amazing facts! – Fossils occur in a particular order – Certain fossils appear in older rocks but not newer ones – This shows that life has changed over time – Out of all the species that have ever lived, 99% of them are extinct! 17-2,17-3 The Evolution of Variation • Up until 1 Billion years ago, the earth consisted of a primordial soup • As oxygen levels in the atmosphere were elevated, more single-cell living organisms appeared. • 1 Billion years ago, prokaryotic cells began reproducing sexually. They also began to join together, creating the first eukaryotic cell. (Endosymbiotic theory) – This led to an increase in variation and the birth of multicellular organisms 17-4 Extinction • Out of all the species that ever lived, only 1% still exist • Extinction of species was caused by many factors, such as: – Competition for resources – Environmental changes – Gradual extinction via natural selection – Mass extinction 17-4 Continued • Mass Extinction – Happens occasionally and wipes out entire ecosystems – Volcanoes, Sea Level changes, and continental drift have all lead to mass extinction – Scientists have reason to believe that an asteroid lead to the extinction of the dinosaurs Is Evolution constant? • Gradualism: Evolution • Punctuated Equilibrium: Evolution happens in happens gradually and continually over a short bursts interrupted by long periods of no long period of time change