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ch25 - Chapter 25 History of Life on Earth Hypothesis...

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Chapter 25 History of Life on Earth Hypothesis: explanation based on observation life arose on planet Earth How did life begin? A few centuries ago o People thought the new living things appeared all of the time Spontaneous Generation Refuted Mid-1800s Louis Pasteur o Broth in flask is boiled to kill pre-existing microorganism o As the broth cools, condensing water collects; sealing the mouth of the flask o If the neck is later broken off, outside air can carry microorganisms into broth Conditions on Earth Atmosphere o Oxygen missing o Similar to Jupiter today o Frequent storms with lots of lightning o Frequent volcanic eruption o Frequent meteor impact o UV light from the sun o No ozone layer Earth Before Life Arose About 4.6 billion years old o Radiometric dating of meteorites and moon rocks Life arose 3.8 billion years ago o Chemical traces in rocks 3.8 billion years ago o No spontaneous generation now, but must have happened then How to Assemble a Living Thing Acculate organic molecules Catalyze reactions Reproduce form genetic information Separate the living things from the outside environment How did the Earliest Cells Do It?
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