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Earth’s Early History:

Earth’s Early History:. The formation of the planet and the beginning of life. An Important Note:.

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Earth’s Early History:

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  1. Earth’s Early History: The formation of the planet and the beginning of life

  2. An Important Note: • These large-scale hypotheses are based on a relatively small amount of hard evidence. Because of this, these exciting inferences will without doubt develop, improve, and even change over time.

  3. How the Planet Formed

  4. Formation of Planet Earth • 4.6 billion years ago • Cosmic debris • Collisions, compression, decay…HEAT

  5. Formation of Planet Earth • Differentiation: • Iron sank • Less dense “floated” to form crust • Least dense = first atmosphere

  6. Earth’s Early Atmosphere • Very different from today’s atmosphere: • Much hotter • Frequent volcanic eruptions • Little or no oxygen • Toxic to us! vs

  7. Setting the Stage for Life • 3.8 billion years ago, Earth cooled, water in liquid form • Global ocean • Here, life will somehow form!

  8. Animation • http://www.precisiongraphics.com/portfolio/animation/

  9. The First Organic Molecules Life cannot begin without these!

  10. How do we get life? Spontaneous Generation Biogenesis • Living things can come from non living things • All living things must come from a living thing In the mid 1600’s Francesco Redi decided to find out…

  11. Redi’s Experiment: Do Flies Spontaneously Generate on Rotting Meat? Control Group Experimental Group • Uncovered jars with rotting meat • Covered jars with rotting meat • Air could pass through but not flies

  12. Results: Biogenesis

  13. Two More Experiments…1700’s LazzaroSpallanzani: • Tried to prove micro-organisms did not come from a “vital force” in the air • Opponents said that he heated the flasks for too long removing the “vital force”

  14. Finally an Answer…mid 1800’s Louis Pasteur • Similar to Spallanzi’s but allows for the air to continue to be exchanged with the outside • Curve prevents solids from passing into the flask • FINALLY Accept Biogenesis

  15. The first Organic Molecules • Could organic molecules have evolved under the conditions of early Earth? • 2 American chemists tried to answer that: • Miller and Urey

  16. Miller and Urey Experiment • Showed that mixtures of organic compounds necessary for life can be created from simpler compounds that were present on early Earth

  17. Important Note: • Not accurate! • Corrected, showed that organic compounds CAN form under these conditions…even cytosine and uracil, two bases found in RNA!

  18. Life’s Origins

  19. Proteinoid Microspheres • Organic molecules forming bubbles • Selectively permeable membranes • Can store and release energy • Similar to modern cell

  20. RNA and DNA • RNA molecules can form • Theory: could these early forms of RNA (that predate more complex DNA and RNA molecules) have found a home inside a microsphere?

  21. Oxygen • The fossil record  photosynthetic bacteria • Rising levels of oxygen in atmosphere • The rise of oxygen drove some life forms to extinction (it was toxic to them), while other life forms were able to thrive

  22. The Beginning of Modern Life Eukaryotic Cell Origins

  23. Origin of Eukaryotic Cells • Prokaryotic cells • Internal membrane  nucleus • Cells with a nucleus! The first eukaryotes!!!

  24. Origin of Eukaryotic Cells • Endosymbiotic Theory

  25. Evolution of Multicellular Life Through 4 eras

  26. Precambrian Era • 650-544 million years ago • Simple anaerobic life forms • Photosynthetic life develops adding oxygen to the atmosphere • Eukaryotes appear • Life still only in the sea!

  27. Paleozoic Era • 544-245 million years ago • Diversity of marine life • First vertebrates • First organisms walked on land • Plants and insects appeared • Mass extinction – 95% of life dies out!

  28. Mesozoic Era • 245-65 million years ago • Appearance of dinosaurs (which later dominate the land on Earth) • Small mammals develop • Leafy trees, shrubs, and flowering plants develop • Mass Extinction – 50% of life dies out

  29. Cenozoic Era • 65 million years ago – present • Plants and insects thrive • Mammals adapt to environment well and dominate life on Earth • Appearance of human ancestors • Ice age

  30. But HOW do we know this? Fossilization and Determining Ages

  31. Fossilization • Fossil = remains or traces of an organism that died long ago • Ways to make a fossil • Sedimentary Rock • Amber • Volcanic Ash

  32. Sedimentary Rock – Relative Dating • Principle of Superposition (1669) – if rock strata (layers) have not been disturbed, the lowest stratum was formed first • Relative Age – age compared to other fossils, determined by location in the strata

  33. Radiometric Dating • Compare the amount of a naturally occurring isotope to its decay products. • Absolute Age – age of the rock as determined by radiometric dating • Half Life – Time it takes for half of the material to decay

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