Chapter 25

Chapter 25 - B iology 1202 Chapter 25 C hapter 25 The H...

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Biology 1202 Chapter 25 Chapter 25 – The History of Life on Earth There are 100 million species on Earth. Hypothesis – definition How did life begin? o A few centuries ago, People thought that new living things appeared all the time (hypothesis of spontaneous generation). o Spontaneous Generation refuted Mid-1800s by Louis Pasteur He boiled broth in a flask to kill any preexisting micro-organisms to show that nothing would grow in a sterile environment. As the broth cools, condensing water collects, sealing the mouth of the flask, and nothing was forming in the solution, which led Pasteur to believe that the life was being generated by microorganisms in the air. If the neck is later broken off, outside air can carry microorganisms into broth. Conditions on early Earth o Atmosphere: CO 2 , CH 4 , NH 3 , H2, N2, HCl, H2S, H2O (very similar to Jupiter’s atmosphere) There was no free oxygen in early earth’s atmosphere Now there is O2 (molecular oxygen) and O3(ozone) There were frequent storms with lots of lightning Frequent volcanic eruptions Molten surface, crust had not yet formed Frequent meteor impacts
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Biology 1202 Chapter 25 Lots of UV radiation from the sun, which caused mutations in the cells of early life forms, which could possibly increase variation in the early populations, hypothetically No ozone layer, no oxygen present o Before Life Arose on Earth Earth is about 4.6 billion years old This dating comes from radiometric dating of meteorites and moon rocks One of the biggest problems with Descent with Modification was that there wasn’t enough time for everything that occurred Life arose about 3.8 billion years ago. Due mostly with fossilized chemical traces of ancient life in rocks that were about 3.8 billion years old o Prokaryotes were simpler, so they existed first (TEST QUESTION) Fossil bacteria in rocks were found about 3.5 billion years old. o Nothing multi-cellular was found yet. If there is no spontaneous generation now, it must’ve happened back then.
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Chapter 25 - B iology 1202 Chapter 25 C hapter 25 The H...

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