Lecture_23 - Life in the Universe Perhaps the most profound...

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1 Life in the Universe Life in the Universe Perhaps the most profound question of all Perhaps the most profound question of all are we alone? are we alone? We, this people, on a small and lonely planet Traveling through casual space Past aloof stars, across the way of indifferent suns To a destination where all signs tell us It is possible and imperative that we learn A brave and startling truth. Maya Angelou Let ’s start s start with life on with life on Earth Earth When did life arise on Earth? When did life arise on Earth? • Earth formed about 4.6 billion years ago • Life arose before 3.85 billion years ago , shortly after the period of heavy bombardment, about 4.2-3.9 billion years ago. • Evidence from fossils , carbon isotopes. 2 billion years of Earth’s history recorded in the Grand Canyon Layers of sediment produced by erosion is carried to the sea and compressed into soft rocks Fossil evidence Fossil evidence Geological time scales • Relative ages: deeper layers formed earlier . • Absolute ages: radiometric dating Fossil evidence for life dates back 3.5 billion years ago • These life forms were already fairly complex because they used sunlight (photosynthesis), thus suggesting a much earlier origin for more primitive life. • Carbon isotopes pushes origin to 3.85 billion years ago . Shark Bay, Western Australia: Colonies of microbes called “living stromatolites” Stromatolites are ancient rocks that show structure similar to bacterial colonies today.
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The Geological Time Scale The Geological Time Scale The universe existed for about 9 billion years before the Sun was formed. Hominids appeared only a few million years ago! EXPANDED VIEW Cambrian Explosion 540 million years ago people First oxygen Remarkable growth in animal diversity The Theory of Evolution The Theory of Evolution (remember that the word “theory” in science represents the highest accolade; you should know that evolution is a fact !) • The fossil record shows that evolution has occurred through time. Species have evolved. • Darwin’s theory tells us HOW evolution occurs: through natural selection . • Theory supported by discovery of DNA : evolution proceeds through genetic mutations . • The basic chemical nature of DNA is virtually identical among all living organisms. This suggest a common ancestry . The Double Helix – the genetic code • Mapping genetic relationships has led biologists to discover the “ tree of life .” Shows genetic similarities. Plants and animals are a small part of the tree . • Suggests likely characteristics of common ancestor Bacteria and Archaea are prokaryotes, cellular organisms without a nucleus; eukaryotes have cells with an enclosed nucleus • These genetic studies suggest that the earliest life on Earth may have resembled the bacteria today found near deep ocean volcanic vents (black smokers) and geothermal hot springs. Bacterial lakes in Yellowstone National Park
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This note was uploaded on 02/20/2012 for the course ASTRO 3 taught by Professor Mclean during the Spring '11 term at UCLA.

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Lecture_23 - Life in the Universe Perhaps the most profound...

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