Chapter 25

Chapter 25 - Chapter 25: H istory of L ife on Earth How did...

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Chapter 25: History of Life on Earth How did life begin? A few centuries ago: o People thought that new living things appeared all of the time Theory of Spontaneous Generation Refuted o Mid 1800s Louis Pasteur ** Had a broth in a flask and boiled it to kill preexisting microorganisms As broth cools, condensing water collects sealing the mouth of the flask Nothing started to grow so So if neck is later broken off, outside air can carry microorganisms into broth o Shows that life does not spontaneously generate out of thin air Problem: life somehow DID spontaneously generated our of thin air on earth Conditions on Early Earth o Atmosphere CO2, CH4, NH3, H2, N2, HCL, H2S, H2O No oxygen in early earths atmosphere! Similar to Jupiter today Frequent storms with lots of lightening Frequent volcanic eruptions Frequent meteor impacts
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UV light from the sun was intense…lack of ozone (0 3 ) Earth before life arose o 4.6 billion years old radiometric dating of meteorites and moon rocks
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Chapter 25 - Chapter 25: H istory of L ife on Earth How did...

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